Nonlinear thermoelectric effect measurement device, nonlinear thermoelectric effect measurement method, nonlinear thermoelectric effect measurement program, recording medium, temperature fluctuation environment power generation element, and temperature fluctuation sensor

Abstract

The present invention addresses the problem of providing a non-linear thermoelectric effect measurement device, a non-linear thermoelectric effect measurement method, a non-linear thermoelectric effect measurement program, a recording medium, a temperature fluctuation environment power generation element, and a temperature fluctuation sensor, whereby temperature fluctuations can be converted into electric energy by a non-linear thermoelectric effect and detected. To this end, a nonlinear thermoelectric effect measurement device for measuring a nonlinear thermoelectric effect generated in a sample is provided with: a temperature gradient generation unit for generating a temperature gradient in the sample; and a potential difference measurement unit that measures a potential difference V generated in the sample, the temperature gradient generation unit being provided with: a first heating unit that is provided on one surface of the sample; and a second heating unit that is provided on the other surface of the sample that faces the one surface, and that applies a first current jc1 = Idc1 + I1sin ([omega] t + [phi]) to the first heating unit and applies a second current jc2 = Idc2 + I2sin ([omega] t) to the second heating unit.

Description

Technical Field

[0001] The present invention relates to a non-linear thermoelectric effect measuring device, a non-linear thermoelectric effect measuring method, a non-linear thermoelectric effect measuring program, a recording medium, a power generation element for a temperature fluctuation environment, and a temperature fluctuation sensor. Background Art

[0002] Conventionally, energy harvesting (environmental power generation) has been proposed to recover various forms of energy around us and convert it into electric energy. In addition, as a type of energy harvesting, a technique has been proposed to harvest electric energy using a thermoelectric conversion element based on a temperature difference generated by the environment (for example, refer to Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-144212 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] Conventionally known thermoelectric conversion elements convert a temperature difference generated by an object into electric energy through the Seebeck effect. Therefore, if the temperature gradient is reversed, the generated electric field is also reversed, so the presence of a stable temperature gradient at the macroscopic scale is essential for power generation. As an environment in which power generation can be performed using such existing thermoelectric conversion elements, examples include exhaust heat from a vehicle using an internal combustion engine and exhaust heat from a factory using a heating device. However, in the real environment, there is no stable temperature gradient, and there are limited scenarios in daily life where existing thermoelectric conversion elements can be used for power generation.

[0008] However, even in an environment that appears to be at a constant temperature at the macroscopic scale, it can be considered that there are cases where the temperature gradient fluctuates in time and space at the microscopic scale. Even in such an environment with a random temperature gradient, if it is possible to convert microscopic temperature fluctuations into electric energy, it may be possible to achieve energy harvesting in more environments.

[0009] Therefore, in view of the above-mentioned existing problems, the present invention aims to provide a non-linear thermoelectric effect measuring device, a non-linear thermoelectric effect measuring method, a non-linear thermoelectric effect measuring program, a recording medium, a power generation element for a temperature fluctuation environment, and a temperature fluctuation sensor that can convert temperature fluctuations into electric energy through a non-linear thermoelectric effect and detect them.

[0010] Means for Solving the Problems

[0011] In order to solve the above problems, a non-linear thermoelectric effect measuring device of the present invention is a non-linear thermoelectric effect measuring device for measuring the non-linear thermoelectric effect generated in a specimen, and includes: a temperature gradient generating unit that generates a temperature gradient in the specimen; and a potential difference measuring unit that measures the potential difference V generated in the specimen. The temperature gradient generating unit includes: a first heating unit provided on one surface of the specimen; and a second heating unit provided on the other surface of the specimen opposite to the one surface, and a first current j is applied to the first heating unit c1 = I dc1 + I1sin(ωt + Φ), and a second current j is applied to the second heating unit c2 = I dc2 + I2sin(ωt).

[0012] In such a non-linear thermoelectric effect measuring device of the present invention, by applying a magnetic field to the specimen to generate a temperature gradient and making the currents flowing through the first heating unit and the second heating unit include a DC current component, an AC current component, and a phase difference, the temperature fluctuation can be converted into electric energy and detected through the non-linear thermoelectric effect.

[0013] In addition, in one aspect of the present invention, a magnetic field applying unit is provided, and the magnetic field applying unit applies a magnetic field to the specimen.

[0014] In addition, in one aspect of the present invention, a phase-locked detection unit is provided, and the phase-locked detection unit detects a component V of frequency 2ω for the potential difference V 2ω .

[0015] In addition, in one aspect of the present invention, a phase change measuring unit is provided, and the phase change measuring unit changes the Φ to obtain the distribution of the component V 2ω .

[0016] In addition, in one aspect of the present invention, an intensity calculation unit is provided, and the intensity calculation unit calculates the non-linear thermoelectric intensity β based on the distribution of the component V obtained by the phase change measuring unit 2ω .

[0017] In addition, in order to solve the above problems, a non-linear thermoelectric effect measuring method of the present invention is a non-linear thermoelectric effect measuring method for measuring the non-linear thermoelectric effect generated in a specimen, and includes: a temperature gradient generating step of generating a temperature gradient in the specimen; and a potential difference measuring step of measuring the potential difference V generated in the specimen. In the temperature gradient generating step, a first current j is applied to a first heating unit provided on one surface of the specimen c1 = I dc1 + I1sin(ωt + Φ), and a second current j is applied to a second heating unit provided on the other surface of the specimen opposite to the one surfacec2 = I dc2 + I2sin(ωt).

[0018] In addition, to solve the above problems, the non-linear thermoelectric effect measurement program of the present invention is a non-linear thermoelectric effect measurement program for causing a computer to measure the non-linear thermoelectric effect generated in the first direction of a specimen, and is used for causing the computer to execute the following steps: a temperature gradient generation step of applying a first current j c1 = I dc1 + I1sin(ωt + Φ) to a first heating part provided on one surface of the specimen, and applying a second current j c2 = I dc2 + I2sin(ωt) to a second heating part provided on the other surface of the specimen opposite to the one surface, to generate a temperature gradient in the specimen; and a potential difference measurement step of measuring the potential difference V generated in the specimen.

[0019] In addition, to solve the above problems, the computer-readable recording medium of the present invention records the above non-linear thermoelectric effect measurement program.

[0020] In addition, to solve the above problems, the power generation element for a temperature fluctuation environment of the present invention includes: a thermoelectric conversion part that generates a potential difference by a non-linear thermoelectric effect due to temperature fluctuations; and a spatial asymmetry part that breaks the spatial symmetry of the thermoelectric conversion part.

[0021] In addition, in one aspect of the present invention, the thermoelectric conversion part and the spatial asymmetry part are made of different materials and have a joining structure of the thermoelectric conversion part and the spatial asymmetry part.

[0022] In addition, in one aspect of the present invention, the thermoelectric conversion part and the spatial asymmetry part are made of the same material layer, and the crystal structure of the material layer does not have inversion symmetry and belongs to a polar point group or a chiral point group.

[0023] In addition, to solve the above problems, the temperature fluctuation sensor of the present invention includes: a thermoelectric conversion part that generates a potential difference by a non-linear thermoelectric effect due to temperature fluctuations; and a spatial asymmetry part that breaks the spatial symmetry of the thermoelectric conversion part.

[0024] In addition, in one aspect of the present invention, the thermoelectric conversion part and the spatial asymmetry part are made of different materials and have a joining structure of the thermoelectric conversion part and the spatial asymmetry part.

[0025] In addition, in one aspect of the present invention, the thermoelectric conversion part and the spatial asymmetry part are made of the same material layer, and the crystal structure of the material layer does not have inversion symmetry and belongs to a polar point group or a chiral point group.

[0026] Advantages of the Invention

[0027] In the present invention, there can be provided a non-linear thermoelectric effect measuring device, a non-linear thermoelectric effect measuring method, a non-linear thermoelectric effect measuring program, a recording medium, a temperature fluctuation environment power generation element, and a temperature fluctuation sensor that can convert temperature fluctuations into electric energy through a non-linear thermoelectric effect and detect the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a block diagram showing the structure of a non-linear thermoelectric effect measuring device 100 according to the first embodiment.

[0029] Figure 2 is a process chart showing the processes of a non-linear thermoelectric effect measuring method according to the first embodiment.

[0030] Figure 3 is a schematic diagram for explaining the measurement of a specimen 10 using the non-linear thermoelectric effect measuring device 100 according to the first embodiment. Figure 3 where (a) shows an example of the specimen 10. Figure 3 where (b) is a conceptual diagram showing the relationship between the magnetic field B, the heat flux j Q and the electric field E.

[0031] Figure 4 is a substitute photograph of a drawing showing the state in which the specimen 10 is provided in the non-linear thermoelectric effect measuring device 100 according to the first embodiment. Figure 4 where (a) and (b) are examples in which the radiator is in contact with both sides of the heaters 30a and 30b. Figure 4 where (c) and (d) are examples in which the radiator is in contact with only one of the heaters 30a and 30b.

[0032] Figure 5 is a graph showing the detection results of the phase-locked detection unit 50 according to the first embodiment. Figure 5 where (a) shows the results of the first order of the heat flux. Figure 5 where (b) shows the results of the 4ω measurement. Figure 5 where (c) shows the measurement results of the second order of the heat flux.

[0033] Figure 6 is a graph showing the distribution of the voltage signal V 2ω obtained by changing the phase difference Φ of the alternating current flowing through the heaters 30a and 30b according to the first embodiment.

[0034] Figure 7 is a graph showing the distribution of the voltage signal V 2ω in various magnetic fields B.

[0035] Figure 8 It is a diagram showing the spontaneous power generation generated in the specimen 10 due to temperature fluctuations. Figure 8 In the upper part of (a) of it, there is a graph showing the degree of vacuum and temperature fluctuations. Figure 8 In the lower part of (a) of it, there is a schematic diagram showing the dc voltage generated in the specimen 10. Figure 8 In (b) of it, there is a graph of the dc voltage generated in the specimen 10 due to temperature fluctuations.

[0036] Figure 9 It shows Figure 8 the peak amplitude A of the dc voltage caused by the temperature fluctuations in dc the graph.

[0037] Figure 10 It is a graph showing the relationship between the magnitude of the heat flux and the distribution of the voltage signal V 2ω and the distribution. Figure 10 In (a) of it, it shows the distribution of the voltage signal V based on various current values applied to the heaters 30a and 30b. 2ω and the distribution. Figure 10 In (b) of it, it shows the relationship between the linear thermoelectric signal intensity and the non-linear thermoelectric signal intensity.

[0038] Figure 11 It is a graph showing the measurement results of the second power of the heat flux in the phase-locked detection unit 50 at various temperatures.

[0039] Figure 12 It is a schematic diagram showing the crystal structure of Te of the specimen 10 related to the fourth embodiment.

[0040] Figure 13 It is a schematic diagram explaining the measurement of the specimen 10 related to the fourth embodiment.

[0041] Figure 14 It shows the linear and non-linear Seebeck coefficients S (1) and S (2) and the magnetic field dependence of the graph. Figure 14 In (a) of it, it shows the first-order term S (1) at 20K. Figure 14 In (b) of it, it shows the second-order term S (2) at 20K. Figure 14 In (c) of it, it shows the first-order term S (1) at 300K. Figure 14 In (d) of it, it shows the second-order term S (2) at 300K.

[0042] Figure 15 It shows the linear and non-linear Seebeck coefficients S (1) and S (2)Graph of the chemical potential dependence Figure 15 In (a) of , the first-order term S at low temperature is shown (1) , Figure 15 In (b) of , the second-order term S at low temperature is shown (2) , Figure 15 In (c) of , the first-order term S at high temperature is shown (1) , Figure 15 In (d) of , the second-order term S at high temperature is shown (2) .

[0043] Figure 16 represents the graphs of the temperature dependences of the linear and nonlinear Seebeck coefficients S (1) 、S (2) , Figure 16 In (a) of , the first-order term S in the low-temperature range is shown (1) , Figure 16 In (b) of , the second-order term S in the low-temperature range is shown (2) , Figure 16 In (c) of , the first-order term S in the high-temperature range is shown (1) , Figure 16 In (d) of , the second-order term S in the high-temperature range is shown (2) . Detailed implementation mode

[0044] (First implementation mode)

[0045] Hereinafter, the implementation modes of the present invention will be described in detail with reference to the drawings. The same or equivalent components, members, and processes shown in the respective drawings are denoted by the same reference numerals, and repeated descriptions will be appropriately omitted Figure 1 is a block diagram showing the structure of the non-linear thermoelectric effect measurement device 100 according to the present implementation mode. The non-linear thermoelectric effect measurement device 100 is realized by controlling each hardware by a computer. A computer is a device that processes various information according to a given process, and includes a central processing unit (CPU: Central Processing Unit), a memory, an external storage device, and various interfaces. In addition, the computer uses various interfaces to Figure 1 connect to each hardware shown in a manner capable of information communication, send control signals to control the operation, and obtain various information from the hardware

[0046] As Figure 1As shown, the non-linear thermoelectric effect measurement device 100 is a device for measuring the non-linear thermoelectric effect of the specimen 10, and includes a magnetic field application unit 20, a temperature gradient generation unit 30, a potential difference measurement unit 40, a phase-locked detection unit 50, a phase change measurement unit 60, and an intensity calculation unit 70. Each of these units performs information processing based on a program recorded in the memory and external storage device of the computer by the CPU, and realizes the process of the non-linear thermoelectric effect measurement method. In addition, a program for the units shown by Figure 1 to execute the non-linear thermoelectric effect measurement method can be recorded in a recording medium, and read into the memory and external storage device of the computer from the recording medium as needed via an electrical information communication line or the like.

[0047] The specimen 10 is the object to be measured by the non-linear thermoelectric effect measurement device 100. The specimen 10 is preferably composed of a material that is supposed to exhibit a non-linear thermoelectric effect. The structure of the specimen 10 is not limited. As an example, a structure or material having a thermoelectric conversion unit that generates a potential difference from temperature fluctuations by the non-linear thermoelectric effect and a spatial asymmetry unit that breaks the spatial symmetry of the thermoelectric conversion unit can be cited. The thermoelectric conversion unit and the spatial asymmetry unit can be configured as a bonding structure based on different materials, or can be composed of the same material layer.

[0048] The magnetic field application unit 20 is a part that applies a magnetic field to the specimen 10. The structure of the magnetic field application unit 20 is not limited, and an electromagnet or a permanent magnet can be used, but an electromagnet is preferably used to control the direction and intensity of the magnetic field. Here, an example of using the magnetic field application unit 20 is shown, but it is used to facilitate the measurement of the non-linear thermoelectric effect by applying a magnetic field, and the structure of omitting the magnetic field application unit 20 can also be set.

[0049] The temperature gradient generation unit 30 is a part that generates a temperature gradient in the specimen 10. The specific structure of the temperature gradient generation unit 30 is not limited. In Figure 1 the example shown, an example in which heaters (heating parts) 30a and 30b are provided on the front and back surfaces of the specimen 10 is shown. In addition, the temperature gradient generation unit 30 includes a heater power supply (not shown) that supplies current to the heaters 30a and 30b. The temperature gradient generation unit 30 controls the current supplied from the heater power supply to the heaters 30a and 30b, makes the temperature difference applied to the specimen 10 change with time, and generates a temperature gradient between the two surfaces of the specimen 10. As described later, a direct current component and an alternating current component are superimposed on the current applied from the temperature gradient generation unit 30 to the heating part. Here, the heater 30a corresponds to the first heating part in the present invention, and the heater 30b corresponds to the second heating part in the present invention.

[0050] The potential difference measurement unit 40 is a part that measures the potential difference generated in the specimen 10. The structure of the potential difference measurement unit 40 is not limited. As an example, a structure can be cited in which two electrodes are formed on the opposing side surfaces of the specimen 10 in a direction orthogonal to the temperature gradient direction and the magnetic field application direction, and the potential difference between the electrodes is measured with a voltmeter.

[0051] The phase-locked detection unit 50 is a part that performs phase-locked detection of a given frequency component based on the change over time with respect to the potential difference measured by the potential difference measurement unit 40. The specific structure of the phase-locked detection unit 50 is not limited, and an existing well-known lock-in amplifier can be used.

[0052] The phase change measurement unit 60 is a part that sets a phase difference for the AC component of the current supplied to the heaters 30a and 30b. By changing the phase difference Φ of the AC components applied to the heaters 30a and 30b and measuring a given frequency component of the potential difference generated in the specimen 10 using the potential difference measurement unit 40, a potential distribution at the phase difference Φ can be obtained.

[0053] The intensity calculation unit 70 is a part that calculates the nonlinear thermoelectric intensity β based on the distribution of the given frequency component obtained by the phase change measurement unit 60. Details of the calculation method for the nonlinear thermoelectric intensity β will be described later.

[0054] Figure 2 is a process chart showing the processes of the nonlinear thermoelectric effect measurement method according to the present embodiment. As Figure 2 shown, in the nonlinear thermoelectric effect measurement method, the specimen 10 is set in Figure 1 the nonlinear thermoelectric effect measurement device 100 shown, starting from a state where the measurement environment such as temperature and vacuum degree is appropriately set.

[0055] Step S1 is a magnetic field application process, in which a magnetic field is applied from the magnetic field application unit 20 to the specimen 10. Step S2 is a temperature gradient generation process, in which a temperature gradient is generated in the specimen 10 by the temperature gradient generation unit 30. Step S3 is a potential difference measurement process, in which the potential difference generated in the specimen 10 is measured using the potential difference measurement unit 40. Step S4 is a phase-locked detection process, in which a given frequency component of the potential difference generated in the specimen 10 is detected using the phase-locked detection unit 50. Step S5 is a phase change measurement process, in which the phase of the thermal gradient applied to the front and back surfaces of the specimen 10 by the temperature gradient generation unit 30 is changed by the phase change measurement unit 60, and a given frequency component of the potential difference is measured. Step S6 is an intensity calculation process, in which the nonlinear thermoelectric intensity β is calculated using the intensity calculation unit 70 based on the distribution of the given frequency component obtained by the phase change measurement unit 60. Details of specific examples of each process will be described later.

[0056] Figure 3This is a schematic diagram for explaining the measurement of the specimen 10 using the non-linear thermoelectric effect measurement device 100 according to this embodiment. Figure 3 (a) of Figure 3 shows an example of the specimen 10. Figure 3 (b) of Figure 3 is a conceptual diagram showing the relationship between the magnetic field B, the heat flux jQ, and the electric field E. In Figure 3 the example shown, the specimen 10 has a laminated structure of a substrate 11, a magnetic insulating layer 12, and a superconducting material layer 13.

[0057] The substrate 11 is a substantially plate-like member that forms the magnetic insulating layer 12 and the superconducting material layer 13 on one surface and holds the magnetic insulating layer 12 and the superconducting material layer 13. The material of the substrate 11 is not limited, and a material capable of forming the magnetic insulating layer 12 is selected. In Figure 3 Figure 3 shows an example of using Gd3Ga5O 12 (GGG) as the substrate 11. As the thickness of the substrate 11, for example, 500 μm can be cited.

[0058] The magnetic insulating layer 12 is a layer made of an electrically insulating magnetic material that is formed on the substrate 11 and has a superconducting material layer 13 formed on its upper surface. The material of the magnetic insulating layer 12 is not limited, and a material capable of being formed on the substrate 11 is selected. In Figure 3 Figure 3 shows an example of using Y3Fe5O 12 (YIG) as the magnetic insulating layer 12. On the substrate 11 made of GGG, the magnetic insulating layer 12 made of YIG can be grown using a conventionally known liquid phase epitaxial growth method. As the thickness of the magnetic insulating layer 12, for example, 3 μm can be cited. Here, the magnetic insulating layer 12 is provided only on one surface side of the superconducting material layer 13, forming a structure that breaks the spatial symmetry when viewed from the superconducting material layer 13, and thus corresponds to the space-asymmetric part in the invention of this application.

[0059] The superconducting material layer 13 is a layer made of a superconducting material that is formed on the upper surface of the magnetic insulating layer 12. The material of the superconducting material layer 13 is not limited, and a material capable of being formed on the magnetic insulating layer 12 is selected. In Figure 3 Figure 3 shows an example of using amorphous MoGe, which is a second superconductor, as the superconducting material layer 13. The superconducting material layer 13 made of MoGe can be formed on the magnetic insulating layer 12 using a conventionally known high-frequency sputtering method. As the thickness of the superconducting material layer 13, for example, 150 nm can be cited. In addition, as the conditions for the high-frequency sputtering method of MoGe, for example, while water-cooling the substrate 11, the Ar pressure is 2.8×10 -1Pa, the growth rate is 5 nm / min, the rotation speed of the substrate 11 is 3000 rpm, etc. Here, the superconducting material layer 13 is a layer that generates a potential difference caused by the thermoelectric effect in a direction perpendicular to the temperature gradient and the magnetic field, and thus corresponds to the thermoelectric conversion part in the invention of the present application.

[0060] After the magnetic insulating layer 12 is grown on the substrate 11 by liquid phase epitaxy and the superconducting material layer 13 is formed on the magnetic insulating layer 12 by high-frequency sputtering, for example, it is cut into an element size of 6 mm × 3 mm, and thus the Figure 3 specimen 10 shown is obtained. As described later, a potential difference is generated in the bonding structure between the magnetic insulating layer 12 and the superconducting material layer 13 through the non-linear thermoelectric effect. Therefore, Figure 3 the specimen 10 shown has a thermoelectric conversion part that exhibits a non-linear thermoelectric effect and a spatial asymmetric part that breaks the spatial symmetry of the thermoelectric conversion part. The thermoelectric conversion part and the spatial asymmetric part are made of different materials and have a bonding structure between the thermoelectric conversion part and the spatial asymmetric part, corresponding to the non-linear thermoelectric effect element in the invention of the present application.

[0061] In addition, a heater 30a and an electrode 31a are provided on the surface of the superconducting material layer 13, and a heater 30b and an electrode 31b are provided on the back surface of the substrate 11. The heaters 30a and 30b are composed of, for example, thin film resistors and generate Joule heat by being supplied with current. The heaters 30a and 30b are respectively provided in contact with the superconducting material layer 13 and the substrate 11, and heat is supplied to the front and back sides of the specimen 10 to generate a temperature gradient between the front and back surfaces. The electrodes 31a and 31b are parts made of a metal material provided on both sides of the heaters 30a and 30b respectively.

[0062] The heater power supplies of the temperature gradient generating part 30 are respectively connected to the electrodes 31a and 31b to supply current to the heaters 30a and 30b. In addition, electrodes (not shown) are also formed on the opposing sides of the superconducting material layer 13, and a potential difference measuring part 40 is connected. Here, the heaters 30a and 30b and the electrodes 31a and 31b can be integrally formed on the front and back surfaces of the specimen 10, or can be formed separately from the specimen 10 and clamp the specimen 10.

[0063] As Figure 3 shown, the plane where the substrate 11 of the specimen 10 extends is set as the xy plane, and the stacking direction of the substrate 11, the magnetic insulating layer 12, and the superconducting material layer 13 is set as the z-axis direction. The direction of the magnetic field B applied by the magnetic field applying part 20 is the y-axis direction, and the direction of the temperature gradient generated by the temperature gradient generating part 30 is the z-axis direction. As Figure 3 (b) of shows, in the superconducting material layer 13, magnetic fluxes (eddy currents: vortex) quantized by the magnetic field B are generated in the y-axis direction. At this time, through the heat flow j based on the temperature gradientQ , an electric field E is generated in the x-axis direction through the thermoelectric effect. Here, the x-axis direction, y-axis direction, and z-axis direction respectively correspond to the first direction, second direction, and third direction in the present invention. In the case where a non-linear heat conduction effect is generated in the superconducting material layer 13, as shown in Figure 3 (b) of, regardless of whether the direction of the heat flux j Q is the positive direction or the negative direction of the z-axis, the direction of the electric field E is the same.

[0064] Figure 4 is a substitute photograph of the drawing showing the state where the specimen 10 is disposed in the non-linear thermoelectric effect measuring device 100 according to the present embodiment, Figure 4 (a) and (b) of are examples in which the heat sink is in contact with both sides of the heaters 30a and 30b, Figure 4 (c) and (d) of are examples in which the heat sink is in contact with only one of the heaters 30a and 30b. In order to measure the thermoelectric effect in the superconducting state of the superconducting material layer 13 of the specimen 10, the non-linear thermoelectric effect measuring device 100 of the present embodiment Figure 4 (a) and (b) of or Figure 4 (c) and (d) of the sample holder shown is housed in a vacuum vessel, and the measurement is performed while changing the magnetic field using a superconducting magnet in an extremely low temperature environment.

[0065] Next, the linear (primary) and non-linear (secondary) thermoelectric effects will be described. In the conventionally known linear thermoelectric effect, the electric field E generated by the heat flux is expressed using the thermoelectric coefficient S and the temperature gradient (∝ heat flux J Q ) as This relationship causes the sign of the electric field E to reverse when the direction of the temperature gradient (∝ heat flux J Q ) is reversed, and satisfies the relationship. Therefore, in the existing linear thermoelectric conversion, thermoelectric power generation can only be performed in an environment where a stable temperature gradient exists on a macroscopic scale.

[0066] In contrast, in the secondary thermoelectric effect, under the condition of broken spatial symmetry, the non-linear relationship and the non-opposite relationship hold. Thus, it is considered that thermoelectric power generation can be performed based on temperature fluctuations on a microscopic scale even in an environment where there is no stable temperature gradient on a macroscopic scale. The inventors of the present invention have successfully measured the secondary thermoelectric effect using the non-linear thermoelectric effect measuring device 100 for the first time in the world.

[0067] Regarding the thermoelectric signal V generated by the thermoelectric effect, if the heat flux J is usedQ It is expressed as [Equation 1]. Here, a (1) is the linear (first-order) term, and a (2) is the non-linear (second-order) term.

[0068]

Equation 1

[0069] V = a (1) j Q + a (2) j Q 2 + a (3) j Q 3 + …

[0070] When an alternating current j c ∝ sin(ωt) with an angular frequency ω flows through the heaters 30a and 30b, the Joule heat j Q is proportional to the square of the current. Therefore, j Q is expressed as [Equation 2]. In addition, if [Equation 2] is substituted into [Equation 1], [Equation 3] is obtained.

[0071]

Equation 2

[0072] j Q ∝ j c 2 ∝ sin 2 (ωt) ∝ 1 - cos(2ωt)

[0073]

Equation 3

[0074] V = a (1) (1 - cos(2ωt)) + a (2) (1 - cos(2ωt)) 2 + a (3) (1 - cos(2ωt)) 3 + …

[0075] = {a (1) + …} cos(2ωt) + {a (2) + a (3) + …} cos(4ωt) + {a (3) + …} cos(6ωt) + …

[0076] Therefore, regarding the potential difference V measured by the potential difference measurement unit 40, by performing phase-locked detection of the angular frequency 2ω by the phase-locked detection unit 50, it is possible to measure the voltage signal V (1) generated by the first-order term (linear) a 2ω of the heat flow. However, even if phase-locked detection is performed at the angular frequency 4ω, since the coefficient of cos(4ωt) in [Equation 3] contains the second-order term a (2)and the cubic term a (3) , so it contains terms other than the quadratic term and the nonlinear thermoelectric effect cannot be measured.

[0077] Therefore, a DC bias current I is added to the alternating current supplied from the temperature gradient generation unit 30 to the heaters 30a and 30b dc to make jc ∝ I dc + I0sin(ωt). In this case, the generated Joule heat j Q is expressed as [Equation 4].

[0078]

Equation 4

[0079] j Q ∝ (I dc + I0sin(ωt)) 2 = I 2 dc + 2I dc I0sin(ωt) + I 2 0sin 2 (ωt)

[0080] Here, the term of sin 2 (ωt) can be transformed into cos(2ωt) in the same way as [Equation 2]. Therefore, for the first-order term of the heat flux, it can be measured by phase-locked detection at 2ω. In addition, regarding the quadratic term a (2) in [Equation 3], it is expressed by [Equation 5]. Since there is a term of sin(ωt), it can be measured as long as double-frequency phase-locked detection at the angular frequency 2ω is used.

[0081]

Equation 5

[0082] a (2 )(I 2 dc + 2I dc I0sin(ωt) + I 2 0sin 2 (ωt))

[0083] However, [Equation 3] also contains the square term of sin of a (1) . In the phase-locked detection at the angular frequency 2ω, it will contain the first-order term (linear) a (1) and the second-order term (nonlinear) a (2) . Since the first-order term is large, the second-order term cannot be extracted only. Therefore, a phase difference Φ is set in the AC components supplied to the heaters 30a and 30b. Specifically, the currents j c1 , j c2 supplied to the heaters 30a and 30b are respectively set as j c1 ∝ I dc1 + I1sin(ωt + Φ), jc2 ∝I dc2 +I2sin(ωt). In this case, the heat flux jQ is represented by [Equation 6].

[0084]

Equation 6

[0085] j Q ∝I 2 dc1 +2I dcl I s in(ωt+Φ)+I 2 1sin 2 (ωt+Φ)-I 2 dc2 -2I dc2 I e sin(ωt)-I 2 2sin 2 (ωt)

[0086] Therefore, by setting I dc1 , I dc2 , I1, I2 such that only the first power terms of sin are retained in [Equation 6], the quadratic term (nonlinearity) a (2) generated by the heat flux can be measured by phase-locked detection at the angular frequency 2ω, and the resulting voltage V 2ω diff . As an example of the process, setting I dc1 = I dc2 , I1 = I2, Φ = 0 as the initial state, the process of changing I1 by the temperature gradient generating unit 30 to eliminate the 2ω phase-locked voltage and the process of changing I2 to eliminate the 1ω phase-locked voltage are repeated, and only the terms of sin(ωt+Φ) and sin(ωt) in [Equation 6] are retained. Then, the phase change measuring unit 60 changes Φ to obtain the distribution of the voltage signal V 2ω .

[0087] Figure 5 is a graph showing the detection result of the phase-locked detection unit 50 according to the present embodiment, Figure 5 (a) of which shows the result of the first order of the heat flux, Figure 5 (b) of which shows the result of the 4ω measurement, Figure 5 (c) of which shows the result of the second order of the heat flux measurement. In the figure, the horizontal axis represents the magnetic field B applied by the magnetic field applying unit 20, the left vertical axis represents the measured voltage in the potential difference measuring unit 40, and the right vertical axis represents the resistance value. In addition, the solid line in the graph represents the thermoelectric signal in the phase-locked detection unit 50, and the dashed line represents the resistance value of the superconducting material layer 13. In addition, T shown in the graph represents the measurement temperature.

[0088] In Figure 5 (a) to Figure 5In each of the curves of (c), it can be seen that in the regions on both sides of the horizontal axis where the absolute value of the magnetic field B is relatively large, the magnetic field B is greater than the critical magnetic field, and there is a resistance value in the superconducting material layer 13, so it is in the normal conducting state. In addition, it can be seen that in the central region of the horizontal axis where the absolute value of the magnetic field B is relatively small, the magnetic field B is smaller than the critical magnetic field, the resistance value of the superconducting material layer 13 is zero, and it is in the superconducting state. Figure 5 of (a) to Figure 5 In the shaded region in (c) of, it is the middle between the superconducting state and the normal conducting state, and it is near the phase transition magnetic field where the resistance value of the superconducting material layer 13 changes rapidly. In the superconducting state, the quantized magnetic flux (eddy current: vortex) in the superconducting material layer 13 is pinned, but near the phase transition temperature, the pinning of the quantized magnetic flux is released to become a vortex liquid, and the eddy current moves freely within the superconducting material layer 13.

[0089] In the present embodiment, as Figure 5 shown in (a) of, the phase-locked detection of the angular frequency 2ω is performed by the phase-locked detection unit 50, and the voltage V generated by the first-order term a of the above-mentioned heat flux is measured. (1) 2ω . In the magnetic field region of the superconducting state, the voltage signal V 2ω is zero, and the thermoelectric effect under the first-order term a of the heat flux is not generated. This can be considered because in the superconducting state, the eddy current is pinned within the superconducting material layer 13 and the movement of the eddy current is not generated due to the heat flux. In contrast, near the phase transition magnetic field of the superconductor, the voltage signal V (1) changes sharply. This can be considered because in this magnetic field region, the pinning of the eddy current is released to become a vortex liquid, the movement of the eddy current is generated due to the heat flux, and a potential difference is generated in the x-axis direction due to the Nernst effect. 2ω

[0090] In addition, as Figure 5 shown in (b) of, when the phase-locked detection unit 50 performs the phase-locked detection of the angular frequency 2ω, the voltage signal V 4ω changes sharply between positive and negative in the vortex liquid. This is because as described above, it includes the second-order term a (2) and the third-order term a (3) of the heat flux, and the non-linear second-order term a (2) cannot be extracted alone.

[0091] As Figure 5 shown in (c) of, when a bias current and an alternating current are applied to the heaters 30a and 30b and a phase difference Φ is set for the alternating current (in the example shown in (c) of Figure 5 , Φ = π), a voltage signal V appears near the phase transition magnetic field 2 ω diff ​​This is probably because, by setting I dc1 ,I dc2 , I1, I2 make only the terms of sin(ωt+Φ) and sin(ωt) retained in [Formula 6], thus only the quadratic term a of the heat flow is extracted (2) In addition, due to the setting of I dc1 ,I dc2 , I1, I2 make only the terms of sin(ωt+Φ) and sin(ωt) remain in [Formula 6], so the voltage signal V (2) 2ω The distribution of should be as shown in [Formula 7].

[0092]

Formula 7

[0093] V 2ω (2) ∝sin 2 (φ / 2)cos(φ)

[0094] Figure 6 is a voltage signal V obtained by changing the phase difference Φ of the AC current flowing through the heaters 30a and 30b according to the present embodiment. 2ω The horizontal axis in the figure represents the phase difference Φ, and the vertical axis represents the voltage signal V 2ω The black dots in the graph are the result of plotting the measured data, and the solid line represents the fitting curve in [Formula 7]. Figure 6 As shown in , the fitting curve based on the function of [Formula 7] above overlaps with the distribution of the measured data. Figure 5 (c) The voltage signal V detected 2ω diff The clear peak signal is obtained through nonlinear thermoelectric conversion based on the quadratic term a(2) of the heat flow.

[0095] Figure 7 is the voltage signal V in various magnetic fields B 2ω The horizontal axis of each curve represents the phase difference Φ, and the vertical axis represents the voltage signal V 2ω The black dots in the graph are the result of plotting the measured data, and the solid line represents the fitting curve. Figure 7 As shown in the left column, below the critical magnetic field, in B = 1T, 1.5T, 2T, and 2.5T, the vortex is pinned in the vortex solid phase, and the fitting curve is not the curve shown in [Formula 7]. Figure 7As shown in the central column, at B = 4.4 T, 4.45 T, 4.5 T, and 4.55 T near the critical magnetic field, it is the vortex liquid phase where vortices can move, and the fitting curve becomes the curve shown in [Equation 7]. As Figure 7 As shown in the right column, at B = 6 T, 7 T, 8 T, and 9 T above the critical magnetic field, it is the normal conducting phase, and the fitting curve is not the curve shown in [Equation 7]. Therefore, it can be confirmed that the Figure 5 explicit peak signal of the detected voltage signal V 2ω diff is the nonlinear vortex Nernst effect generated by the quadratic term of the heat flux in the vortices.

[0096] Figure 8 is a graph showing the self - power generation generated in the specimen 10 due to temperature fluctuations. Figure 8 The upper part of (a) of Figure 8 is a graph showing the degree of vacuum and temperature fluctuations, and the lower part of (a) of Figure 8 is a schematic diagram showing the dc voltage generated in the specimen 10. Figure 8 In the graph shown in the upper part of (a) of Figure 8 , the horizontal axis represents the passage of time, and the vertical axis represents the temperature fluctuation ΔT. 2 The dashed line in the upper part of (a) of －5 represents the case of a low vacuum with a vacuum degree of about 10

[0097] Figure 8 The graph of (b) of dc is a graph that sets the current supply from the temperature gradient generation unit 30 to the heaters 30a and 30b to zero and only plots the voltage measured by the potential difference measurement unit 40. In the graph, the horizontal axis represents the magnetic field B, and the vertical axis represents the measurement result V dc in the potential difference measurement unit 40. The dashed line in the graph represents the case of low vacuum and large temperature fluctuations, and the solid line represents the case of high vacuum and small temperature fluctuations. The voltage V

[0098] Figure 9 represents Figure 8 the peak amplitude A dc of the dc voltage caused by the temperature fluctuations in Figure 9 . The vertical axis of dc represents the peak amplitude A dc where the change amount of the voltage VFigure 8 , Figure 9 In the example shown in Figure 9 , the peak amplitude A is small under high vacuum and small temperature fluctuations, dc and the peak amplitude A is large under low vacuum and large temperature fluctuations. dc Therefore, by detecting the change in the peak amplitude A, dc it is possible to detect the change in temperature fluctuations in the specimen 10.

[0099] In Figure 8 , Figure 9 examples are shown where the peak amplitude A is small under small temperature fluctuations dc and the peak amplitude A is large under large temperature fluctuations. dc However, it is also possible to use a specimen 10 where the peak amplitude A is large under small temperature fluctuations dc and the peak amplitude A is small under large temperature fluctuations. dc Also in this case, the temperature fluctuation sensor can detect the change in temperature fluctuations in the specimen 10 by detecting the change in the peak amplitude A. dc

[0100] Figure 10 is a graph showing the relationship between the magnitude of heat flow and the distribution of the voltage signal V2ω, Figure 10 (a) of which shows the distribution of the voltage signal V 2ω for various current values applied to the heaters 30a, 30b, Figure 10 (b) of which shows the relationship between the linear thermoelectric signal intensity and the non-linear thermoelectric signal intensity. Figure 10 In (a) of Figure 10 , the horizontal axis represents the phase difference Φ and the vertical axis represents the voltage signal V. 2ω The magnetic field B is measured in the range of -3.7T to -3.825T, and the actuating current value I H flowing through the heaters 30a, 30b is changed from 0.35 mA to 3.25 mA for measurement. When the actuating current value I H flowing through the heaters 30a, 30b becomes larger, the temperature gradient and heat flow intensity applied to the specimen 10 become larger, and the amplitude of the curve shown in [Equation 7] also becomes larger.

[0101] Taking Figure 10 the difference between the maximum value and the minimum value of the voltage signal V 2ω in the graph shown in (a) of Figure 10 as the non-linear thermoelectric signal intensity A 2ω . In addition, taking the amplitude of (a) of Figure 10 corresponding to the first-order term a(1) of [Equation 3] as the linear thermoelectric signal intensity A Figure 5 . 1ω Figure 10 In (b) of Figure 10 , the horizontal axis represents the linear thermoelectric signal intensity A 1ω, the vertical axis represents the non-linear thermoelectric signal intensity A 2ω . Figure 10 The graph shown in (b) is based on each execution current value I H to calculate A 1ω and A 2ω and the result of plotting. The solid line in the graph represents the quadratic function fitted using the least squares method. At this time, if the coefficient β of the quadratic function is set as the non-linear thermoelectric coefficient, then A 1ω and A 2ω The relationship is represented by [Equation 8]. The calculation of this non-linear thermoelectric coefficient β is performed by the intensity calculation unit 70.

[0102]

Equation 8

[0103] A 2ω ∝β(A 1ω ) 2

[0104] In Figure 10 In the example shown in (b), the non-linear thermoelectric coefficient β = 4.5×10 calculated by the intensity calculation unit 70 5 m -2 kg -1 s 3 A. Therefore, the sample 10 having the bonding structure of the superconducting material layer 13 made of MoGe as the thermoelectric conversion unit and the magnetic insulating layer 12 as the space asymmetry unit can be said to have a non-linear thermoelectric coefficient β = 4.5×10 5 m -2 kg - 1 s 3 A temperature fluctuation environment power generation element.

[0105] Figure 11 is a graph showing the quadratic measurement results of the heat flow in the phase-locked detection unit 50 at various temperatures. In the figure, the horizontal axis represents the magnetic field B applied by the magnetic field application unit 20, the left vertical axis represents the measurement voltage in the potential difference measurement unit 40, and the right vertical axis represents the resistance value. Since the critical magnetic field increases at low temperatures, the magnetic field at which the peak signal of the voltage signal V 2ω also increases. As Figure 11 shown, in the non-linear thermoelectric effect measurement device 100 of the present embodiment, the non-linear thermoelectric effect in the sample 10 can be detected regardless of the temperature.

[0106] As described above, in the non-linear thermoelectric effect measurement device 100, non-linear thermoelectric effect measurement method, non-linear thermoelectric effect measurement program, recording medium, temperature fluctuation environment power generation element, and temperature fluctuation sensor of the present embodiment, there are provided: a magnetic field application unit 20 that applies a magnetic field in the y-axis direction of the sample 10; a temperature gradient generation unit 30 that generates a temperature gradient in the z-axis direction; and a potential difference measurement unit 40 that measures the potential difference V generated in the x-axis direction of the sample 10. The temperature gradient generation unit 30 includes a heater 30a provided on one surface of the sample 10 and a heater 30b provided on the other surface. By applying a first current j c1 =I dc1 +I1sin(ωt + Φ) and a second current j c2 =I dc2 +I2sin(ωt), it is possible to convert temperature fluctuations into electric energy through the non-linear thermoelectric effect and detect it. In addition, by measuring the voltage V dc generated in the sample 10 and detecting the change in the peak amplitude A dc , a temperature fluctuation sensor for detecting temperature fluctuations can be constituted.

[0107] (Second Embodiment)

[0108] Next, a second embodiment of the present invention will be described. Descriptions of the content repeated in the first embodiment will be omitted. In the first embodiment, as the temperature fluctuation environment power generation element, the joining structure of the superconducting material layer 13 as the thermoelectric conversion unit and the magnetic insulating layer 12 as the space asymmetry unit is shown, but the thermoelectric conversion unit and the space asymmetry unit are not limited to the combination of the superconducting material layer 13 and the magnetic insulating layer 12. As candidate materials for the thermoelectric conversion unit, substances with a large non-linearity of conductivity can be cited, such as Te, MoS2, ferromagnetic metal / paramagnetic metal bilayer films, etc. In addition, ferromagnetic conductors belonging to the polar point group that breaks time and space inversion symmetry can be cited.

[0109] The combination of the thermoelectric conversion unit and the space asymmetry unit preferably requires "breaking of space symmetry" and has any one of "breaking of time inversion symmetry", "Berry phase dipole mechanism", and "asymmetric scattering mechanism based on impurities, etc.". Here, breaking of space symmetry means that the atomic configuration in the thermoelectric conversion unit becomes asymmetric when the space is inverted. In addition, temperature fluctuation means the spatial or temporal non-uniformity of temperature in the thermoelectric conversion unit. In addition, the thermoelectric conversion unit preferably has electrical conductivity. In addition, as substances with breaking of time inversion symmetry, magnetic materials and substances with octopole moments can be cited.

[0110] (Third Embodiment)

[0111] Next, a third embodiment of the present invention will be described. Descriptions of the same content as in the first embodiment will be omitted. In the first embodiment, as a temperature fluctuation environment power generation element, a bonding structure of a superconducting material layer 13 as a thermoelectric conversion unit and a magnetic insulating layer 12 as a space asymmetry unit is shown, but the thermoelectric conversion unit and the space asymmetry unit may also be composed of the same material layer.

[0112] The material layer constituting the thermoelectric conversion unit and the space asymmetry unit is a substance that exhibits a nonlinear thermoelectric effect and has a molecular structure that breaks space symmetry. As such a material layer, a material layer whose crystal structure does not have inversion symmetry and belongs to a polar point group or a chiral point group can be cited. More specifically, a material belonging to 21 point groups within 32 point groups whose crystal structures themselves do not have inversion symmetry, and among the 21 point groups, belonging to a polar point group (1, 2, m, mm2, 3, 3m, 4, 4mm, 6, 6mm) or a chiral point group (1, 2, 222, 4, 422, 3, 32, 6, 622, 23, 432) can be cited. In addition, in addition to having the above crystal structure, the material layer needs to further satisfy at least one requirement among "breaking of time-reversal symmetry", "Berry phase dipole mechanism", and "asymmetric scattering mechanism based on impurities, etc.".

[0113] When the thermoelectric conversion unit and the space asymmetry unit of the temperature fluctuation environment power generation element are composed of the same material layer, a temperature gradient is generated by the temperature gradient generation unit 30 in the direction in which the crystal structure of the material layer does not have inversion symmetry. More specifically, heaters 30a and 30b are provided on the front and back surfaces in the direction in which the crystal structure of the material layer does not have inversion symmetry, and the same current as in the first embodiment is supplied to the heaters 30a and 30b. In addition, a magnetic field is applied by the magnetic field application unit 20 in a direction perpendicular to the temperature gradient direction, and the potential difference generated in a direction perpendicular to the temperature gradient direction and the magnetic field direction is measured by the potential difference measurement unit 40.

[0114] (Fourth Embodiment)

[0115] Next, Figures 12 to 16 A fourth embodiment of the present invention will be described. Descriptions of the same content as in the first embodiment will be omitted. In this embodiment, Te whose crystal structure belongs to the chiral point group is used as the specimen 10, and the first term and the second term of the Seebeck coefficient are confirmed by theoretical calculation, which is different from the first embodiment.

[0116] Figure 12 is a schematic diagram showing the crystal structure of Te as the specimen 10 according to this embodiment. Figure 12 The spheres shown in represent Te atoms, and the lines connecting the Te atoms represent bonding bonds. In Figure 12In (a), the vertical direction in the figure represents the c-axis direction of the crystal structure, and the horizontal direction in the figure represents the a-axis direction of the crystal structure. In Figure 12 In (b), the direction perpendicular to the paper surface represents the c-axis direction of the crystal structure, the horizontal direction in the figure represents the a-axis direction of the crystal structure, and the upper left oblique direction in the figure represents the b-axis direction of the crystal structure. As Figure 12 shown in (a) and (b) of Figure 12 , the Te single crystal has a chiral structure in which three Te atoms are arranged in a triangular spiral with the c-axis as the spiral axis. Therefore, the specimen 10 composed of the Te single crystal becomes a structure that breaks the spatial symmetry in the c-axis direction, and thus corresponds to the space-asymmetric part in the invention of the present application.

[0117] Figure 13 FIG. is a schematic diagram for explaining the measurement of the specimen 10 according to the present embodiment. In Figure 13 the example shown in Figure 13 , a Te single crystal as the specimen 10 is disposed on a substrate composed of an insulating layer 80a and a conductive layer 80b. As Figure 13 shown by the arrow indicating the coordinate system in Figure 13 , the length direction of the substrate is set as the z-axis direction, and the width direction is set as the x-axis direction. In addition, heaters 30a and 30b are provided to extend along the x-axis direction on the surface of the insulating layer 80a. Electrodes (not shown) are provided at both ends in the x-axis direction of the heaters 30a and 30b.

[0118] Heater power supplies of the temperature gradient generating unit 30 are respectively connected to the electrodes provided at both ends of the heaters 30a and 30b to supply current to the heaters 30a and 30b. In addition, electrodes (not shown) are also formed at both ends in the z-axis direction of the specimen 10, and a potential difference measuring unit 40 is connected. The specimen 10 is mounted on the substrate such that the c-axis of the crystal structure becomes the z-axis direction, and a magnetic field is also applied along the z-axis direction.

[0119] Similar to the first embodiment, an external magnetic field B is applied to the specimen 10 in the z-axis direction, and an electric field E is generated in the z-axis direction by the thermoelectric effect caused by the temperature gradient Here, the z-axis direction corresponds to the first direction in the present invention. When a non-linear thermoelectric effect is generated in the specimen 10, the magnitude of the electric field E is different depending on whether the direction of the temperature gradient is the positive direction or the negative direction of the z-axis. Here, since the temperature gradient is in a proportional relationship with the heat flux jQ, the discussion about the heat flux jQ described in the first embodiment can be treated synonymously with the temperature gradient Therefore, obtaining the first-order term a (1) and the second-order term a (2) of the heat flux in the first embodiment is synonymous with obtaining the linear and non-linear Seebeck coefficients S (1) , S (2) .

[0120] In this embodiment, the sample 10 made of Te single crystal is a layer that generates a potential difference caused by the thermoelectric effect in the temperature gradient direction and the magnetic field application direction, and thus corresponds to the thermoelectric conversion unit in the invention of this application. Therefore, the sample 10 in this embodiment includes a thermoelectric conversion unit that exhibits a non-linear thermoelectric effect and a spatial asymmetry unit that breaks the spatial symmetry of the thermoelectric conversion unit, and can be used as a power generation element and a temperature fluctuation sensor in the temperature fluctuation environment in the invention of this application.

[0121] Next, the first-order and second-order terms of the Te single crystal of the sample 10 with respect to the temperature gradient are studied. First, the Hamiltonian operator in the Te single crystal of the sample 10 is defined by [Equation 9]. Here, g is the g factor, and μ B is the Bohr magneton.

[0122]

Equation 9

[0123]

[0124] When an electric field E is generated parallel to the c-axis of the sample 10, the Boltzmann equation is the following [Equation 10]. e is the elementary charge, and τ is the relaxation time that depends on the elementary charge and the value of the substance.

[0125]

Equation 10

[0126]

[0127] Here, the distribution function f = f0 + f1 + f2 + ···, and f n ∝E n , f0 := 1 / (1 + exp(−β(E − μ))), β = 1 / k B T, k B is the Boltzmann constant, T is the temperature, and μ is the chemical potential, the first-order term f1 and the second-order term f2 become [Equation 11].

[0128]

Equation 11

[0129]

[0130] Therefore, the current j e generated by the electric field, the first-order term j e (1) and the second-order term j e (2) are represented by [Equation 12].

[0131]

Equation 12

[0132]

[0133] Here, σ after removing the coefficient is defined by [Equation 13]. (1) and σ (2) .

[0134]

Equation 13

[0135]

[0136] When a temperature gradient is generated parallel to the c-axis of the specimen 10 the Boltzmann equation becomes the following [Equation 14].

[0137]

Equation 14

[0138]

[0139] Here, when it is set as the linear term f1 and the quadratic term f2 of f = f0 + f1 + f2 + ··· become [Equation 15].

[0140]

Equation 15

[0141]

[0142] In the case where the temperature gradient is constant, since the last term is deleted, and the linear term j e of the current j e (1) and the quadratic term j e (2) generated by the temperature gradient are expressed by [Equation 16].

[0143]

Equation 16

[0144]

[0145] Here, α after removing the coefficient is defined by [Equation 17]. (1) and α (2) .

[0146]

Equation 17

[0147]

[0148] The current j z generated in the c-axis direction of the specimen 10 is the current j z parallel to the c-axis direction based on the electric field E e and the current j based on the temperature gradient e sum. Using σ (1) defined by [Equation 12], [Equation 13] to [Equation 16], [Equation 17], σ (2) , α(1) , α (2) It is expressed by [Formula 18].

[0149]

Formula 18

[0150]

[0151] Here, let the current j z = 0 and solve for E z When the relevant quadratic equation is solved, we obtain [Formula 19].

[0152]

Formula 19

[0153]

[0154] Therefore, the linear first-order term S of the Seebeck coefficient is (1) and the nonlinear quadratic term S (2) It is expressed by [Formula 20].

[0155]

Formula 20

[0156]

[0157] exist Figures 14 to 16 The results of numerical calculations for the above-mentioned [Formula 20] are shown in FIG. Figure 14 Is the linear and nonlinear Seebeck coefficient S (1) , S (2) The magnetic field dependence of Figure 14 (a) represents the first-order term S at 20K (1) , Figure 14 (b) represents the quadratic term S at 20K (2) , Figure 14 (c) represents the first-order term S at 300K (1) , Figure 14 (d) represents the quadratic term S at 300K (2) The horizontal axis in the figure represents the magnetic field B, and the vertical axis represents S (1) or S (2) The values ​​of (arbitrary units) are shown in the figure. Each line in the figure shows the calculation results when the chemical potential μ is changed from -15 meV to -5 meV.

[0158] like Figure 14 (a) and Figure 14 As shown in (c), the first-order term S (1) At low and high temperatures, it is independent of the magnetic field B and becomes constant. Figure 14 (b) and Figure 14 As shown in (d), the quadratic term S (2) It becomes an odd function of the magnetic field B at low and high temperatures.

[0159] Figure 15 represents the linear and non-linear Seebeck coefficients S (1) and S (2) as a graph of the chemical potential dependence, Figure 15 where (a) of represents the linear term S (1) at low temperatures, Figure 15 and (b) of represents the quadratic term S (2) at low temperatures, Figure 15 and (c) of represents the linear term S (1) at high temperatures, Figure 15 and (d) of represents the quadratic term S (2) at high temperatures. Here, the magnetic field B is set to 2 T. In addition, the horizontal axis in the figure represents the chemical potential μ, and the vertical axis represents S (1) or S (2) values (in arbitrary units). In the measurement device shown in Figure 13 , by changing the gate voltage applied between the conductive layer 80b and the sample 10, the chemical potential μ can be changed. Figure 15 The lines in (a) and (b) of represent the calculation results when the temperature T is changed from 4 K to 20 K. Figure 15 The lines in (c) and (d) of represent the calculation results when the temperature T is changed from 100 K to 300 K.

[0160] As shown in (a) to (d) of Figure 15 to Figure 15 , the linear term S (1) and the quadratic term S (2) change according to the chemical potential μ at low and high temperatures. In addition, in the case of low temperature, the change in the linear term S (1) or the quadratic term S (2) with respect to the change in the chemical potential μ becomes larger.

[0161] Figure 16 is a graph showing the temperature dependence of the linear and non-linear Seebeck coefficients S (1) and S (2) , Figure 16 where (a) of represents the linear term S (1) in the low temperature range, Figure 16 and (b) of represents the quadratic term S (2) in the low temperature range, Figure 16 and (c) of represents the linear term S (1) in the high temperature range, Figure 16 and (d) of represents the quadratic term S (2) in the high temperature range. Here, the chemical potential μ is set to 4 meV and the magnetic field B is set to 2 T. In addition, the horizontal axis in the figure represents the temperature T, and the vertical axis represents S (1) or S (2) ​​​Value (in arbitrary units).

[0162] As Figure 16 shown in (a) to Figure 16 shown in (d), the intensity of the linear term S (1) and the quadratic term S (2) both monotonically increase with decreasing temperature T in the low-temperature region and the high-temperature region.

[0163] As Figures 14 to 15 shown, in the region where the quadratic term S (2) of the nonlinear Seebeck coefficient takes a non-zero finite value, using the nonlinear thermoelectric effect measurement device and the nonlinear thermoelectric effect measurement method shown in the first embodiment, the quadratic term S (2) of the nonlinear Seebeck coefficient can be measured. In addition, in the region where the quadratic term S (2) of the nonlinear Seebeck coefficient takes a non-zero finite value, the sample 10 can be used as a temperature fluctuation environment power generation element based on the nonlinear thermoelectric effect. Further, by measuring the voltage V dc generated in the sample 10 and detecting the change in the peak amplitude A dc , a temperature fluctuation sensor for detecting temperature fluctuations can be constructed.

[0164] The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. Embodiments obtained by appropriately combining technical means separately disclosed in different embodiments are also included in the technical scope of the present invention.

[0165] Symbol Explanation

[0166] 100: Nonlinear thermoelectric effect measurement device

[0167] 10: Sample

[0168] 20: Magnetic field application unit

[0169] 30: Temperature gradient generation unit

[0170] 40: Potential difference measurement unit

[0171] 50: Phase-locked detection unit

[0172] 60: Phase change measurement unit

[0173] 70: Intensity calculation unit

[0174] 11: Substrate

[0175] 12: Magnetic insulating layer

[0176] 13: Superconducting material layer

[0177] 30a, 30b: Heater

[0178] 31a, 31b: electrodes

[0179] 80a: insulating layer

[0180] 80b: conductive layer.

Claims

1. A non-linear thermoelectric effect measuring device for measuring the non-linear thermoelectric effect generated in a specimen, wherein, the non-linear thermoelectric effect measuring device includes: a temperature gradient generating unit that generates a temperature gradient in the specimen; and a potential difference measuring unit that measures the potential difference V generated in the specimen, the temperature gradient generating unit includes: a first heating unit disposed on one surface of the specimen; and a second heating unit disposed on the other surface of the specimen opposite to the one surface, Apply a first current j to the first heating part c1 = I dc1 + I1sin(ωt + Φ), and apply a second current j to the second heating part c2 = I dc2 + I2sin(ωt).

2. The non-linear thermoelectric effect measuring device according to claim 1, wherein, the non-linear thermoelectric effect measuring device includes a magnetic field applying unit that applies a magnetic field to the specimen.

3. The non-linear thermoelectric effect measuring device according to claim 1 or 2, wherein, The non-linear thermoelectric effect measurement device includes a lock-in detection unit that detects a component V of frequency 2ω of the potential difference V 2ω .

4. The non-linear thermoelectric effect measuring device according to claim 3, wherein, The non-linear thermoelectric effect measurement device includes a phase change measurement unit that changes the Φ to obtain the distribution of the component V. 2ω ​ 5. The non-linear thermoelectric effect measuring device according to claim 4, wherein, The non-linear thermoelectric effect measurement device includes an intensity calculation unit that calculates the non-linear thermoelectric intensity β based on the distribution of the component V obtained by the phase change measurement unit. 2ω ​ 6. A method for measuring a nonlinear thermoelectric effect, which is used to measure the nonlinear thermoelectric effect generated in a specimen, wherein, the non-linear thermoelectric effect measuring method includes: a temperature gradient generating step of generating a temperature gradient in the specimen; and a potential difference measuring step of measuring the potential difference V generated in the specimen, In the temperature gradient generation step, a first current j is applied to a first heating portion provided on one surface of the specimen c1 = I dc1 + I1sin(ωt + Φ), and a second current j is applied to a second heating portion provided on the other surface of the specimen facing the one surface c2 = I dc2 + I2sin(ωt).

7. A non-linear thermoelectric effect measuring program for causing a computer to measure the non-linear thermoelectric effect generated in a specimen, the non-linear thermoelectric effect measuring program for causing a computer to execute the following steps: A temperature gradient generation step of applying a first current j to a first heating part disposed on one surface of the specimen c1 = I dc1 + I1sin(ωt + Φ), applying a second current j to a second heating part disposed on the other surface of the specimen opposite to the one surface; c2 = I dc2 + I2sin(ωt), causing a temperature gradient to be generated in the specimen; and a potential difference measuring step of measuring the potential difference V generated in the specimen.

8. A computer-readable recording medium recording the non-linear thermoelectric effect measuring program according to claim 7.

9. A power generation element for a temperature fluctuation environment, which includes: a thermoelectric conversion unit that generates a potential difference by a non-linear thermoelectric effect due to temperature fluctuations; and a spatial asymmetry unit that breaks the spatial symmetry of the thermoelectric conversion unit.

10. The power generation element for a temperature fluctuation environment according to claim 9, wherein, the thermoelectric conversion unit and the spatial asymmetry unit are made of different materials and have a joining structure of the thermoelectric conversion unit and the spatial asymmetry unit.

11. The power generation element for a temperature fluctuation environment according to claim 9, wherein, the thermoelectric conversion unit and the spatial asymmetry unit are made of the same material layer, and the crystal structure of the material layer does not have inversion symmetry and belongs to a polar point group or a chiral point group.

12. A temperature fluctuation sensor, which includes: a thermoelectric conversion unit that generates a potential difference by a non-linear thermoelectric effect due to temperature fluctuations; and a spatial asymmetry unit that breaks the spatial symmetry of the thermoelectric conversion unit.

13. The temperature fluctuation sensor according to claim 12, wherein, the thermoelectric conversion unit and the spatial asymmetry unit are made of different materials and have a joining structure of the thermoelectric conversion unit and the spatial asymmetry unit.

14. The temperature fluctuation sensor according to claim 12, wherein, the thermoelectric conversion unit and the spatial asymmetry unit are made of the same material layer, and the crystal structure of the material layer does not have inversion symmetry and belongs to a polar point group or a chiral point group.

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