Device and method for measuring physical parameters of superconducting film

Abstract

The invention provides a measuring device and measuring method for physical parameters of a superconducting thin film, the measuring device comprises a measuring structure and a magnetic field generator, the measuring structure comprises a body part and a mutual inductance coil, and the body part is provided with a cavity; the cavity is used for accommodating a superconducting thin film and filling ionic liquid; the body part comprises a plurality of active electrodes and a regulation and control electrode; the plurality of active electrodes comprise a first current electrode, a second current electrode, a first Hall electrode and a second Hall electrode which are distributed at intervals; the first current electrode is arranged in the first marginal area, the second current electrode is arranged in the third marginal area, the first Hall electrode is arranged in the second marginal area, and the second Hall electrode is arranged in the fourth marginal area. The mutual inductance coil is positioned on at least one side of the superconducting film; the magnetic field generator is located outside the cavity. And the corresponding carrier concentration and the London penetration depth can be obtained through in-situ regulation and measurement, so that a quantification rule that the London penetration depth of the superconducting thin film changes along with the change of the carrier concentration is established.

Description

Technical Field

[0001] The present application relates to the technical field of superconductors, and in particular to a device and method for measuring physical parameters of a superconducting film. Background Art

[0002] The current technologies that can measure the London penetration depth include mutual inductance coils (including reflective mutual inductance and transmission mutual inductance). In the related technologies, the scheme of using mutual inductance coils to achieve in-situ regulation and measurement of the London penetration depth of superconducting films needs to be further optimized. Summary of the invention

[0003] The embodiment of the present application provides a device for measuring physical parameters of a superconducting thin film, comprising:

[0004] A measuring structure, comprising a main body and a mutual inductance coil, wherein the main body is provided with a cavity; the cavity is used to accommodate a superconducting film and to fill an ionic liquid; the main body comprises a plurality of active electrodes and a control electrode; the control electrode and the active electrode are configured to drive ions in the ionic liquid to be doped into the superconducting film through a control voltage therebetween; the plurality of active electrodes are located on a surface of the superconducting film away from the bottom surface of the cavity, and the plurality of active electrodes comprise a first current electrode, a second current electrode, a first Hall electrode and a second Hall electrode distributed at intervals; the surface of the superconducting film away from the cavity comprises a first edge region, a second edge region, a third edge region and a fourth edge region, the first edge region and the third edge region are arranged opposite to each other and both extend in a first direction, the second edge region and the fourth edge region are arranged opposite to each other and both extend in a second direction, and the first direction is perpendicular to the second direction; the first current electrode is arranged in the first edge region, the second current electrode is arranged in the third edge region, the first Hall electrode is arranged in the second edge region, and the second Hall electrode is arranged in the fourth edge region; the mutual induction coil is located on at least one side of the superconducting film, and is used to apply a mutual induction magnetic field to the superconducting film and obtain a mutual induction signal generated by a change in the magnetic field inside the superconducting film;

[0005] The magnetic field generator is located outside the cavity and is used to apply a Hall magnetic field in a direction perpendicular to the bottom surface of the cavity to the superconducting film.

[0006] In some embodiments, the length of the first edge region in the first direction is a first length, and the length of the first current electrode in the first direction is greater than or equal to one-half of the first length and less than or equal to the first length;

[0007] And / or, the length of the third edge region in the first direction is the second length, and the length of the second current electrode in the first direction is greater than or equal to one half of the second length and less than or equal to the second length.

[0008] In some embodiments, the length of the second edge region in the second direction is a third length, the third length is greater than or equal to 5 mm, and the length of the first Hall electrode in the second direction is greater than or equal to 500 μm and less than or equal to one tenth of the third length;

[0009] And / or, the length of the fourth edge region in the second direction is a fourth length, the fourth length is greater than or equal to 5 mm, and the length of the second Hall electrode in the second direction is greater than or equal to 500 μm and less than or equal to one tenth of the fourth length.

[0010] In some embodiments, the main body also includes a detachably connected base and a top cover, the base is provided with a receiving groove, the receiving groove and the top cover form the cavity; a partial area of ​​the opening of the receiving groove is not covered by the top cover; the measuring structure also includes a lead, the lead is connected to the active electrode, and the lead passes through the area of ​​the opening of the receiving groove that is not covered by the top cover and exposes the cavity.

[0011] In some embodiments, the top cover includes a main body and a plurality of branch parts connected to the main body, and the interval area between adjacent branch parts exposes a partial area of ​​the opening of the receiving groove.

[0012] In some embodiments, the cavity includes a central region and an edge region surrounding the central region, the depth of the edge region is greater than the depth of the central region, and the control electrode is located in the edge region and surrounds the central region.

[0013] In some embodiments, the magnetic field generator includes a Helmholtz coil group, and the Helmholtz coil group includes a first Helmholtz coil and a second Helmholtz coil, which are respectively located on opposite sides of the bottom surface of the cavity.

[0014] This embodiment further provides a method for measuring physical parameters of a superconducting thin film. Based on the aforementioned measuring device, the measuring method includes:

[0015] Applying a control voltage between the control electrode and the active electrode to drive the ions in the ionic liquid to be doped into the superconducting film;

[0016] When the superconducting film is in a normal state, the magnetic field generator is controlled to apply a Hall magnetic field in a direction perpendicular to the bottom surface of the cavity to the superconducting film, and a Hall current is applied between the first current electrode and the second current electrode to obtain a Hall voltage between the first Hall electrode and the second Hall electrode.

[0017] In some embodiments, after applying a control voltage between the control electrode and the active electrode to drive the ions in the ionic liquid to be doped into the superconducting film, the measurement method further comprises: when the superconducting film is in a superconducting state, driving the mutual inductance coil to apply a mutual inductance magnetic field to the superconducting film and obtaining a mutual inductance signal generated by a change in the magnetic field inside the superconducting film; wherein,

[0018] The step of obtaining the mutual inductance signal generated by the change of the magnetic field inside the superconducting film is performed after the step of obtaining the Hall voltage between the first Hall electrode and the second Hall electrode, and after the step of obtaining the Hall voltage between the first Hall electrode and the second Hall electrode, and before the step of obtaining the mutual inductance signal generated by the change of the magnetic field inside the superconducting film, the measurement method further includes: cooling the superconducting film and monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly changes to zero, and determining that the superconducting film is converted into a superconducting state;

[0019] or,

[0020] The step of obtaining the mutual inductance signal generated by the change of the magnetic field inside the superconducting film is performed before the step of obtaining the Hall voltage between the first Hall electrode and the second Hall electrode. Before the step of obtaining the mutual inductance signal generated by the change of the magnetic field inside the superconducting film, the measurement method further includes: cooling the superconducting film and monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly changes to zero, and determining that the superconducting film is converted to a superconducting state; after the step of obtaining the mutual inductance signal generated by the change of the magnetic field inside the superconducting film and before the step of obtaining the Hall voltage between the first Hall electrode and the second Hall electrode, the measurement method further includes: controlling the magnetic field generator to apply a gradually changing Hall magnetic field to the superconducting film, and monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly changes to greater than zero, and determining that the superconducting film is converted from a superconducting state to a normal state.

[0021] In some embodiments, monitoring the resistance of the superconducting film comprises:

[0022] Applying a Hall current between the first current electrode and the second current electrode, obtaining a Hall voltage between the first Hall electrode and the second Hall electrode, and calculating the Hall resistance of the superconducting film;

[0023] Alternatively, an ohmic current is applied between the first current electrode and the first Hall electrode, an ohmic voltage is obtained between the second current electrode and the second Hall electrode, and the ohmic resistance of the superconducting film is calculated.

[0024] The beneficial effects of this application include:

[0025] The measuring device provided in this embodiment can apply a constant current to the superconducting film by connecting the first current electrode and the second current electrode to an external current source. The magnetic field generator can be used to apply a Hall magnetic field B to the superconducting film. Z , the Hall voltage of the superconducting film can be obtained by connecting an external voltmeter to the first Hall electrode and the second Hall electrode, and the Hall resistance of the superconducting film can be calculated by the Hall voltage and current. The carrier concentration inside the superconducting film can be further calculated in combination with the calculation formula, and the carrier concentration can be used to characterize the doping degree of the superconducting film. At the same time, the measuring device provided in this embodiment can also apply a mutual inductance magnetic field to the superconducting film through a mutual inductance coil and obtain a mutual inductance signal generated by the change of the magnetic field inside the superconducting film, further establish a calculation function and formula, and simulate and solve to obtain the London penetration depth of the superconducting film. The control voltage can be adjusted to make the superconducting film at different doping levels, and the corresponding carrier concentration and London penetration depth can be measured in situ, thereby establishing a quantitative law of the change of the London penetration depth of the superconducting film with the change of the carrier concentration.

[0026] Additional aspects and advantages of the present application will be partially given in the following description, which will become apparent from the following description, or will be understood through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0028] Figure 1 Shown is a schematic structural diagram of a device for measuring physical parameters of a superconducting thin film provided by an exemplary embodiment of the present application;

[0029] Figure 2 Shown is a cross-sectional schematic diagram of a structure for measuring physical parameters of a superconducting thin film provided by an exemplary embodiment of the present application;

[0030] Figure 3 Shown is a cross-sectional schematic diagram of a structure for measuring physical parameters of a superconducting thin film provided by an exemplary embodiment of the present application;

[0031] Figure 4 Shown is a schematic diagram of the distribution state of active electrodes in a structure for measuring physical parameters of a superconducting thin film provided by an exemplary embodiment of the present application;

[0032] Figure 5 Shown Figure 4 a top view of the structure shown;

[0033] Figure 6 Shown Figure 2 An exploded view of a portion of the components of the measurement structure shown;

[0034] Figure 7 Shown Figure 6 A top view of the measurement structure shown;

[0035] Figure 8 Shown Figure 3 Schematic diagram of the three-dimensional structure of the measurement structure shown. DETAILED DESCRIPTION

[0036] The following is a detailed description of the device and method for measuring the physical parameters of the superconducting thin film in the embodiments of the present application in conjunction with the accompanying drawings. In the absence of conflict, the features in the following embodiments can complement or be combined with each other.

[0037] Although terms such as "first", "second", etc. can be used to describe various components, such components are not limited by the above terms. These terms are only used to distinguish one component from another component, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, the meaning of "multiple" is two or more.

[0038] In the accompanying drawings, the symbols "x", "y" and "z" are used to indicate directions. The x, y and z directions can represent three mutually perpendicular directions in a rectangular coordinate system. For example, x and y can represent a first direction and a second direction mutually perpendicular to each other on a horizontal plane, and z can represent a vertical direction.

[0039] The present application embodiment provides a device for measuring the physical parameters of a superconducting film, such as Figure 1 As shown, the measuring device includes a measuring structure and a magnetic field generator, wherein Figure 2 or Figure 3As shown, the measurement structure includes a main body and a mutual inductance coil, the main body is provided with a cavity; the cavity is used to accommodate the superconducting film and to fill the ionic liquid; the main body includes a plurality of active electrodes and a control electrode; the control electrode and the active electrode are configured to drive the ions in the ionic liquid to be doped into the superconducting film through the control voltage between them. Figure 4 As shown, multiple active electrodes are located on the surface of the superconducting film away from the bottom of the cavity, and the multiple active electrodes include a first current electrode and a second current electrode, a first Hall electrode and a second Hall electrode that are spaced apart; the surface of the superconducting film away from the cavity includes a first edge region, a second edge region, a third edge region and a fourth edge region, the first edge region and the third edge region are relatively arranged and both extend along a first direction x, the second edge region and the fourth edge region are relatively arranged and both extend along a second direction y, and the first direction x is perpendicular to the second direction y; the first current electrode is arranged in the first edge region, the second current electrode is arranged in the third edge region, the first Hall electrode is arranged in the second edge region, and the second Hall electrode is arranged in the fourth edge region. Figure 2 or Figure 3 As shown, the mutual inductance coil is located on at least one side of the superconducting film, and is used to apply a mutual inductance magnetic field to the superconducting film and obtain a mutual inductance signal generated by a change in the magnetic field inside the superconducting film; Figure 1 As shown, the magnetic field generator is located outside the cavity and is used to apply a Hall magnetic field B perpendicular to the bottom surface of the cavity to the superconducting film. Z .

[0040] The measuring device provided in this embodiment can apply a constant current to the superconducting film by connecting the first current electrode and the second current electrode to an external current source. The magnetic field generator can be used to apply a Hall magnetic field B to the superconducting film. Z , the Hall voltage of the superconducting film can be obtained by connecting an external voltmeter to the first Hall electrode and the second Hall electrode, and the Hall resistance of the superconducting film can be calculated by the Hall voltage and current. The carrier concentration inside the superconducting film can be further calculated in combination with the calculation formula, and the carrier concentration can be used to characterize the doping degree of the superconducting film. At the same time, the measuring device provided in this embodiment can also apply a mutual inductance magnetic field to the superconducting film through a mutual inductance coil and obtain a mutual inductance signal generated by the change of the magnetic field inside the superconducting film, further establish a calculation function and formula, and simulate and solve to obtain the London penetration depth of the superconducting film. The control voltage can be adjusted to make the superconducting film at different doping levels, and the corresponding carrier concentration and London penetration depth can be measured in situ, thereby establishing a quantitative law of the change of the London penetration depth of the superconducting film with the change of the carrier concentration.

[0041] It should be noted that the calculation formula for the carrier concentration inside the superconducting film is: Among them, B Z is the Hall magnetic field, I xis the current flowing through the superconducting film, d is the thickness of the superconducting film, V H is the Hall voltage, q is the charge of the carrier (q = -e for electrons, q = +e for holes, where e is the elementary charge).

[0042] In some embodiments, the mutual inductance coil includes a driving coil and a receiving coil, the driving coil is used to apply a mutual inductance magnetic field to the superconducting film, and the receiving coil is used to measure the mutual inductance coefficient M(ω) at different frequencies (ω). The London penetration depth can be solved by establishing a functional relationship between the mutual inductance coefficient and the London penetration depth and fitting. In one example, the functional relationship is as follows: Mutual inductance coefficient M(ω)≈M0(1-ω 2 λ 2 ), where M0 is the mutual inductance when no superconducting film is provided, ω is the angular frequency, and λ is the London penetration depth.

[0043] In some embodiments, the measuring device further includes a phase-locked amplifier (not shown in the figure), which is connected to the driving coil and the receiving coil and is used to apply an alternating current to the driving coil to generate a mutual inductance magnetic field. The mutual inductance magnetic field further changes the magnetic field inside the superconducting film. The phase-locked amplifier is used to measure the induced voltage in the receiving coil to further obtain the mutual inductance coefficient. For example, the magnitude range of the mutual inductance magnetic field is 1×10 -3 ~1×10 -2 G (Gaussian).

[0044] In some embodiments, Figure 1 As shown, the magnetic field generator includes a Helmholtz coil group, and the Helmholtz coil group includes a first Helmholtz coil and a second Helmholtz coil, which are respectively located on opposite sides of the bottom surface of the cavity. It can be used to apply a Tesla-level Hall magnetic field B to the superconducting film. Z .

[0045] In some embodiments, Figure 2 As shown, the mutual inductance coil includes a driving coil and a receiving coil, which are distributed on opposite sides of the superconducting film, and each includes a pair of coils wound in opposite directions and connected in series. The mutual inductance coil constitutes a transmission type mutual inductance coil.

[0046] In some embodiments, Figure 3 As shown, the mutual inductance coil includes a driving coil and a receiving coil, and the driving coil and the receiving coil are both located on the same side of the superconducting film. The axes of the driving coil and the receiving coil coincide, and the receiving coil is symmetrically distributed on both sides of the driving coil. The receiving coil includes a pair of coils that are wound in opposite directions and connected in series. The mutual inductance coil constitutes a reflective mutual inductance coil.

[0047] In some embodiments, Figure 4 and Figure 5As shown, the surface of the superconducting film away from the bottom of the cavity is square, and the active electrodes are distributed around the square at intervals. Figure 2 or Figure 3 As shown, when the ions in the ionic liquid are driven to be doped into the superconducting film by the control voltage between the control electrode and the active electrode, the control electrode and the active electrode can be connected to the two ends of the power supply respectively through the lead wire, and the magnitude of the control voltage can be adjusted by the electrical connector, and the opening and closing of the control voltage can be controlled to achieve the control of the doping degree of the ionic liquid into the superconducting film. In some embodiments, the first current electrode, the second current electrode, the first Hall electrode and the second Hall electrode in the plurality of active electrodes are all connected to one end of the power supply, and the control electrode is connected to the other end of the power supply. Since the active electrodes are spaced around, during the doping (ion injection) process, the doping degree of the ions in each part of the superconducting film is relatively uniform, which can improve the accuracy of the measurement results.

[0048] In some embodiments, the material of the active electrode includes metal. Preferably, the material of the active electrode may be gold.

[0049] In some embodiments, the ohmic resistance of the superconducting film can also be further measured by a four-probe method. Specifically, an ohmic current can be applied between the first current electrode and the first Hall electrode by an external current source, and an external voltmeter can be connected to the second current electrode and the second Hall electrode to obtain an ohmic voltage, and the ohmic resistance of the superconducting film can be calculated to characterize the electrical parameters of superconducting films with different doping levels.

[0050] In some embodiments, Figure 5 As shown, the length of the first edge region in the first direction x is the first length l1, and the length x1 of the first current electrode in the first direction x is greater than or equal to one-half of the first length l1 and less than or equal to the first length l1. This can avoid the current electrode being too short, causing the Hall current to diverge instead of flowing in a straight line. Preferably, the length x1 of the first current electrode in the first direction x is equal to the first length l1. This can achieve that when a constant current is applied between the first current electrode and the second current electrode, the current flows in a straight line along the second direction y as much as possible, which can improve the accuracy of the measurement result of the Hall resistance of the superconducting film.

[0051] In some embodiments, Figure 5 As shown, the length of the third edge region in the first direction x is the second length l2, and the length x2 of the second current electrode in the first direction x is greater than or equal to one half of the second length l2 and less than or equal to the second length l2. The beneficial effects are the same as those of the above embodiments.

[0052] In some embodiments, the length of the first edge region in the first direction x is a first length l1, and the length x1 of the first current electrode in the first direction x is greater than or equal to one-half of the first length l1 and less than or equal to the first length l1. The length of the third edge region in the first direction x is a second length l2, and the length x2 of the second current electrode in the first direction x is greater than or equal to one-half of the second length l2 and less than or equal to the second length l2. Further, when the surface of the superconducting film away from the bottom surface of the cavity is square, the length x1 of the first current electrode in the first direction x can be equal to the length x2 of the second current electrode in the first direction x.

[0053] In some embodiments, the length of the second edge region in the second direction y is a third length l3, the third length l3 is greater than or equal to 5 mm, and the length x3 of the first Hall electrode in the second direction y is greater than or equal to 500 μm and less than or equal to one tenth of the third length l3; in this embodiment, when the length x3 of the first Hall electrode in the second direction y is greater than or equal to 500 μm, it is convenient for the first Hall electrode to be connected to the voltmeter to measure the Hall voltage of the superconducting film. When the length x3 of the first Hall electrode in the second direction y is less than or equal to one tenth of the third length l3, the influence of the shunting between the first Hall electrode and the second Hall electrode on the distribution and flow of the current in the first direction x can be avoided.

[0054] In some embodiments, the length of the fourth edge region in the second direction y is a fourth length l4, the fourth length l4 is greater than or equal to 5 mm, and the length x4 of the second Hall electrode in the second direction y is greater than or equal to 500 μm and less than or equal to one tenth of the fourth length l4. The beneficial effects are the same as those of the above embodiments.

[0055] In some embodiments, the length of the second edge region in the second direction y is a third length l3, the third length l3 is greater than or equal to 5 mm, and the length x3 of the first Hall electrode in the second direction y is greater than or equal to 500 microns and less than or equal to one tenth of the third length l3; the length of the fourth edge region in the second direction y is a fourth length l4, the fourth length l4 is greater than or equal to 5 mm, and the length x4 of the second Hall electrode in the second direction y is greater than or equal to 500 microns and less than or equal to one tenth of the fourth length l4.

[0056] In some embodiments, in combination Figure 2 , Figure 6 As shown, the main body also includes a detachably connected base and a top cover, the base is provided with a receiving groove, and the receiving groove and the top cover form a cavity; Figure 7As shown, part of the opening of the receiving groove is not covered by the top cover; the measuring device also includes a lead (not shown in the figure), which is connected to the active electrode on the surface of the superconducting film, and the lead passes through the area of ​​the opening of the receiving groove that is not covered by the top cover (that is, the gap in the figure) and exposes the cavity.

[0057] In this embodiment, when the receiving tank and the top cover are connected by screws, part of the opening of the receiving tank is not covered by the top cover, and a gap is formed in the area of ​​the opening of the receiving tank not covered by the top cover. When measuring the Hall resistance of the superconducting film, the lead wire can be led out from the active electrode surface in the cavity and passed through the gap to connect an external measuring instrument or circuit structure. Therefore, it is convenient to measure, and compared with the method of leading the lead wire from the side, routing the wire from the top can avoid the risk of ionic liquid leakage caused by the side lead wire.

[0058] In some embodiments, Figure 7 As shown, the top cover includes a main body and a plurality of branch parts connected to the main body, and the interval area between adjacent branch parts exposes a partial area of ​​the opening of the accommodating groove.

[0059] In this embodiment, the top cover is designed to be in the shape of multiple branches, each branch can expose a part of the opening of the accommodating groove (that is, Figure 7 The gap in the middle) can also improve the stability and supporting capacity of the top cover structure. So that a top cover coil support can be further arranged on the main body to accommodate and support the driving coil.

[0060] In some embodiments, the angles between any two adjacent branches are the same. This can further improve the stability and balance of the structure. Figure 7 As shown, the top cover includes a main body and three branch parts, and the angle between any two adjacent branch parts is 120°.

[0061] In some embodiments, Figure 6 and Figure 7 As shown, in this embodiment, when a transmission-type mutual inductance coil is used, the top cover is provided with a top cover coil support, and the receiving groove is provided with a receiving groove coil support. The driving coil is received in the top cover coil support, and the receiving coil is located in the receiving groove coil support. Further, in other embodiments, the driving coil is located in the receiving coil support, and the receiving coil is located in the top cover coil support.

[0062] In some embodiments, Figure 8 As shown, when the reflective mutual inductance coil is used in this embodiment, a mutual inductance coil holder is provided in the receiving groove for accommodating the coaxially arranged driving coil and receiving coil.

[0063] In some embodiments, Figure 6 , Figure 7 or Figure 8As shown, the main body is provided with a plurality of pins, and the leads from the active electrode / regulating electrode on the superconducting film can be connected to the pins and fixed, and then connected to the measuring instrument or circuit structure. The pins can fix the leads, reducing the risk of the lead position being offset or the electrical connection with the superconducting film failing. In addition, the pins can be designed to be made of metal material to improve the thermal conductivity of the measuring structure.

[0064] In some embodiments, the lead wire is made of metal material, which can further enhance the thermal conductivity between the lead wire and the superconducting film, thereby facilitating the measurement of physical parameters of the superconducting film under low temperature conditions.

[0065] In some embodiments, Figure 2 As shown, the cavity includes a central area and an edge area surrounding the central area, the depth of the edge area is greater than the depth of the central area, and the control electrode is located in the edge area and surrounds the central area. The contact area between the control electrode and the ionic liquid can be increased while reducing the relative distance between the driving coil and the receiving coil. The efficiency of ion implantation into the superconducting film can be improved while increasing the strength of the mutual inductance signal.

[0066] In some embodiments, the base / top cover / screws of the present application include insulating materials, which can reduce signal interference to the mutual inductance signal and improve the measurement accuracy of the mutual inductance signal compared to metal materials. In one example, the base and the top cover are made of sapphire, and the screws are made of plastic.

[0067] Based on the same inventive concept, the present application also provides a method for measuring the physical parameters of a superconducting film. Figure 2 or Figure 3 As shown, the following steps are included:

[0068] Step 100: applying a control voltage between the control electrode and the active electrode to drive ions in the ionic liquid to be doped into the superconducting film;

[0069] Step 200: When the superconducting film is in a normal state, the magnetic field generator is controlled to apply a Hall magnetic field B in a direction perpendicular to the bottom surface of the cavity to the superconducting film. Z , applying a Hall current between the first current electrode and the second current electrode, and obtaining a Hall voltage between the first Hall electrode and the second Hall electrode.

[0070] In this embodiment, a first current electrode, a second current electrode, a first Hall electrode and a second Hall electrode are arranged on the superconducting film, and a Hall current is applied to obtain a Hall voltage, and a Hall magnetic field B is combined with the Hall magnetic field B. Z, the carrier concentration of the superconducting film is calculated according to the calculation formula, so that when a control voltage is applied between the control electrode and the active electrode to control the ion doping degree of the superconducting film, the quantitative data of the doping degree can be monitored and obtained, and the parameters characterizing the physical properties of the superconducting film can be further measured to obtain the quantitative law of the change of the parameter with the doping degree.

[0071] It should be noted that when the superconducting film is in a normal state, that is, the Hall resistance / Ohm resistance of the superconducting film is not zero, in contrast, when the superconducting film is in a superconducting state, the Hall resistance / Ohm resistance is zero.

[0072] In some embodiments, when the superconducting film is in a normal state, the Hall magnetic field B applied to the superconducting film by the magnetic field generator is controlled. Z The magnetic induction intensity is about 2T (Tesla). Furthermore, in this embodiment, a gradually changing magnetic field (sweeping field) can be applied to the superconducting film, and the range of the magnetic field change is -2T to 2T. The slope K of the Hall resistance changing with the magnetic field is further obtained, and the carrier concentration is calculated by combining the K value with the formula.

[0073] In some embodiments, after step 100, the measuring method further includes:

[0074] Step 300: When the superconducting film is in a superconducting state, the mutual inductance coil is driven to apply a mutual inductance magnetic field to the superconducting film and obtain a mutual inductance signal generated by a change in the magnetic field inside the superconducting film.

[0075] This embodiment can further control the regulating voltage to adjust the carrier concentration corresponding to different doping levels of the superconducting film, and obtain the London penetration depth corresponding to different doping levels of the superconducting film by measuring the mutual inductance signal, and simulate the quantitative law of the change of the London penetration depth of the superconducting film with the carrier concentration.

[0076] In some embodiments, the magnitude of the mutual induction magnetic field is in the range of 1×10 -3 G (Gauss) ~ 1×10 -2 G (Gaussian)

[0077] In some embodiments, the ion doping level can be adjusted by controlling the magnitude of the regulation voltage or the on / off time.

[0078] In some embodiments, step 300 is performed after step 200. After step 200 and before step 300, the measurement method further includes:

[0079] Step 400: Cooling the superconducting film while monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly changes to zero, thereby determining that the superconducting film is converted into a superconducting state.

[0080] In this embodiment, when the resistance of the superconducting film suddenly changes to zero, it means that the temperature of the superconducting film has reached the critical temperature. At this time, the superconducting film has been converted from a normal state to a superconducting state, and the London penetration depth of the superconducting film can be further measured.

[0081] In some embodiments, the cooling treatment of the superconducting film in step 400 includes: cooling the ionic liquid until the temperature of the superconducting film immersed in the ionic liquid is lower than the critical temperature.

[0082] Since the solidification temperature of the ionic liquid is usually higher than the critical temperature of the superconducting film, in this embodiment, during the cooling process of the ionic liquid, when the temperature is reduced to the solidification temperature of the ionic liquid, the ionic liquid changes from a liquid state to a solidified state. At this time, the ion injection of the ionic liquid stops, and the ion doping degree of the superconducting film can be fixed at the solidification moment. Then the temperature continues to be lowered until the temperature of the superconducting film is lower than the critical temperature, and the resistance of the superconducting film suddenly changes to zero. At this time, the mutual inductance magnetic field can be applied to the superconducting film through the mutual inductance coil to measure the London penetration depth of the superconducting film. Since the ion doping degree of the superconducting film is fixed during the measurement, the problem that the doping degree is still changing during the measurement process and the value of the London penetration depth obtained by the measurement cannot accurately correspond can be avoided. This can improve the accuracy of the measurement results of the London penetration depth.

[0083] In some embodiments, after step 100 and before step 200, the measuring method includes: cooling the ionic liquid until the ionic liquid changes from a liquid state to a solidified state.

[0084] In this embodiment, before measuring the Hall resistance of the superconducting film in step 200, the ionic liquid is changed from a liquid state to a solidified state in advance, so that the ion doping degree of the superconducting film can be fixed at the solidification moment. Since the solidification temperature of the ionic liquid is higher than the critical temperature of the superconducting film, when the temperature is lowered to a temperature range lower than the solidification temperature of the ionic liquid and higher than the critical temperature of the superconducting film, the superconducting film is in a normal state; further, step 200 can be performed. While measuring the Hall resistance in step 200, the ion doping degree of the superconducting film is fixed, which can avoid the problem that the doping degree is still changing during the measurement process, thereby causing the measured Hall resistance value to not accurately correspond. This can improve the accuracy of the measurement result of the Hall resistance. The accuracy of the measurement result of the carrier concentration of the superconducting film can be further improved.

[0085] In some embodiments, the critical temperature of the superconducting film is in a range of greater than 0 and less than 200K, and the freezing point of the ionic liquid is in a range of greater than or equal to 200K and less than or equal to 400K.

[0086] In some embodiments, step 300 is performed before step 200. After step 100 and before step 300, the measurement method further includes step 400': cooling the superconducting film while monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly changes to zero, and determining that the superconducting film is converted to a superconducting state. After step 300 and before step 200, the measurement method further includes step 500: controlling the magnetic field generator to apply a gradually changing Hall magnetic field B to the superconducting film. Z , and at the same time monitor the resistance of the superconducting film until the resistance of the superconducting film suddenly becomes greater than zero, determining that the superconducting film is converted from a superconducting state to a normal state.

[0087] In this embodiment, the superconducting film can be directly cooled. When the resistance of the superconducting film suddenly changes to zero, it means that the temperature of the superconducting film has dropped below the critical temperature. At this time, the superconducting film is converted from a normal state to a superconducting state. Then, the magnetic field generator is controlled to apply a gradually changing Hall magnetic field B to the superconducting film. Z , while monitoring the resistance of the superconducting film. When the resistance of the superconducting film suddenly changes to greater than zero, it means that the Hall magnetic field B Z The magnetic field strength is greater than the critical magnetic field of the superconducting film, which can convert the superconducting film from a superconducting state to a normal state. Therefore, this embodiment can measure the Hall resistance of the superconducting film and further obtain the carrier concentration of the superconducting film when the temperature of the superconducting film is lower than the critical temperature.

[0088] In some embodiments, the magnetic induction intensity of the critical magnetic field of the superconducting film ranges from 7 to 9 T. It should be noted that the critical magnetic field of the superconducting film is determined by the specific material properties of the superconducting film, and the range provided in this embodiment is only an exemplary range.

[0089] In some embodiments, cooling the superconducting film in step 400' includes cooling the ionic liquid until the temperature of the superconducting film immersed in the ionic liquid is lower than the critical temperature. The technical features and beneficial effects of this embodiment are the same as those of step 400, and will not be described in detail here.

[0090] In some embodiments, monitoring the resistance of the superconducting film in step 400 / 400' specifically includes the following steps:

[0091] A Hall current is applied between the first current electrode and the second current electrode, a Hall voltage between the first Hall electrode and the second Hall electrode is obtained, and the Hall resistance of the superconducting film is calculated.

[0092] In this embodiment, the Hall resistance can be monitored online to determine whether the superconducting film is in a normal state or a superconducting state.

[0093] In some embodiments, monitoring the resistance of the superconducting film in step 400 / 400' specifically includes the following steps: applying an ohmic current between the first current electrode and the first Hall electrode, obtaining an ohmic voltage between the second current electrode and the second Hall electrode, and calculating the ohmic resistance of the superconducting film.

[0094] In this embodiment, the ohmic resistance can be monitored online to determine whether the superconducting film is in a normal state or a superconducting state. In this embodiment, it is not necessary to apply a Hall magnetic field B to the superconducting film. Z , thus reducing the power consumption of the magnetic field generator.

[0095] In other embodiments, the mutual inductance signal of the superconducting film can also be monitored to determine whether the superconducting film is in a normal state or a superconducting state. When the value of the mutual inductance signal of the superconducting film is large, the superconducting film is in a normal state, and when the value of the mutual inductance signal of the superconducting film suddenly changes from a large value to a value much smaller than the large value, it can be determined that the state of the superconducting film is converted from a normal state to a superconducting state.

[0096] It should be understood that the embodiments described herein should be considered in a descriptive sense only and not for the purpose of limitation. The description of features or aspects within each embodiment should generally be considered as other similar features or aspects that can be used in other embodiments. Although one or more embodiments have been described with reference to the accompanying drawings, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope defined by the claims and their equivalents.

Claims

1. A device for measuring physical parameters of a superconducting thin film, characterized in that: include: A measuring structure, comprising a main body and a mutual inductance coil, wherein the main body is provided with a cavity; the cavity is used to accommodate a superconducting film and to fill an ionic liquid; the main body comprises a plurality of active electrodes and a control electrode; the control electrode and the active electrode are configured to drive ions in the ionic liquid to be doped into the superconducting film through a control voltage therebetween; the plurality of active electrodes are located on a surface of the superconducting film away from the bottom surface of the cavity, and the plurality of active electrodes comprise a first current electrode, a second current electrode, a first Hall electrode and a second Hall electrode distributed at intervals; the surface of the superconducting film away from the cavity comprises a first edge region, a second edge region, a third edge region and a fourth edge region, the first edge region and the third edge region are arranged opposite to each other and both extend in a first direction, the second edge region and the fourth edge region are arranged opposite to each other and both extend in a second direction, and the first direction is perpendicular to the second direction; the first current electrode is arranged in the first edge region, the second current electrode is arranged in the third edge region, the first Hall electrode is arranged in the second edge region, and the second Hall electrode is arranged in the fourth edge region; the mutual induction coil is located on at least one side of the superconducting film, and is used to apply a mutual induction magnetic field to the superconducting film and obtain a mutual induction signal generated by a change in the magnetic field inside the superconducting film; The magnetic field generator is located outside the cavity and is used to apply a Hall magnetic field in a direction perpendicular to the bottom surface of the cavity to the superconducting film.

2. The device for measuring the physical parameters of a superconducting thin film according to claim 1, characterized in that: The length of the first edge region in the first direction is a first length, and the length of the first current electrode in the first direction is greater than or equal to one half of the first length and less than or equal to the first length; And / or, the length of the third edge region in the first direction is the second length, and the length of the second current electrode in the first direction is greater than or equal to one half of the second length and less than or equal to the second length.

3. The device for measuring the physical parameters of a superconducting thin film according to claim 1, characterized in that: The length of the second edge region in the second direction is a third length, the third length is greater than or equal to 5 mm, and the length of the first Hall electrode in the second direction is greater than or equal to 500 μm and less than or equal to one tenth of the third length; And / or, the length of the fourth edge region in the second direction is a fourth length, the fourth length is greater than or equal to 5 mm, and the length of the second Hall electrode in the second direction is greater than or equal to 500 μm and less than or equal to one tenth of the fourth length.

4. The device for measuring the physical parameters of a superconducting thin film according to claim 1, characterized in that: The main body also includes a base and a top cover that are detachably connected, the base is provided with a receiving groove, the receiving groove and the top cover form the cavity; a partial area of ​​the opening of the receiving groove is not covered by the top cover; the measuring structure also includes a lead wire, the lead wire is connected to the active electrode, and the lead wire passes through the area of ​​the opening of the receiving groove that is not covered by the top cover and exposes the cavity.

5. The device for measuring the physical parameters of a superconducting thin film according to claim 4, characterized in that: The top cover includes a main body and a plurality of branch parts connected to the main body, and a spacing area between adjacent branch parts exposes a partial area of ​​the opening of the accommodating groove.

6. The device for measuring the physical parameters of a superconducting thin film according to claim 5, characterized in that: The cavity includes a central area and an edge area surrounding the central area. The depth of the edge area is greater than the depth of the central area. The control electrode is located in the edge area and surrounds the central area.

7. The device for measuring the physical parameters of a superconducting thin film according to claim 1, characterized in that: The magnetic field generator comprises a Helmholtz coil group, and the Helmholtz coil group comprises a first Helmholtz coil and a second Helmholtz coil, which are respectively located on two opposite sides of the bottom surface of the cavity.

8. A method for measuring physical parameters of a superconducting thin film, characterized in that: Based on the measuring device according to any one of claims 1 to 7, the measuring method comprises: Applying a control voltage between the control electrode and the active electrode to drive the ions in the ionic liquid to be doped into the superconducting film; When the superconducting film is in a normal state, the magnetic field generator is controlled to apply a Hall magnetic field in a direction perpendicular to the bottom surface of the cavity to the superconducting film, and a Hall current is applied between the first current electrode and the second current electrode to obtain a Hall voltage between the first Hall electrode and the second Hall electrode.

9. The method for measuring the physical parameters of a superconducting thin film according to claim 8, characterized in that: After applying a control voltage between the control electrode and the active electrode to drive the ions in the ionic liquid to be doped into the superconducting film, the measurement method further comprises: when the superconducting film is in a superconducting state, driving the mutual inductance coil to apply a mutual inductance magnetic field to the superconducting film and obtaining a mutual inductance signal generated by a change in the magnetic field inside the superconducting film; wherein, The step of obtaining the mutual inductance signal generated by the change of the magnetic field inside the superconducting film is performed after the step of obtaining the Hall voltage between the first Hall electrode and the second Hall electrode, and after the step of obtaining the Hall voltage between the first Hall electrode and the second Hall electrode, and before the step of obtaining the mutual inductance signal generated by the change of the magnetic field inside the superconducting film, the measurement method further includes: cooling the superconducting film and monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly changes to zero, and determining that the superconducting film is converted into a superconducting state; or, The step of obtaining the mutual inductance signal generated by the change of the magnetic field inside the superconducting film is performed before the step of obtaining the Hall voltage between the first Hall electrode and the second Hall electrode. Before the step of obtaining the mutual inductance signal generated by the change of the magnetic field inside the superconducting film, the measurement method further includes: cooling the superconducting film and monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly changes to zero, and determining that the superconducting film is converted to a superconducting state; after the step of obtaining the mutual inductance signal generated by the change of the magnetic field inside the superconducting film and before the step of obtaining the Hall voltage between the first Hall electrode and the second Hall electrode, the measurement method further includes: controlling the magnetic field generator to apply a gradually changing Hall magnetic field to the superconducting film, and monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly changes to greater than zero, and determining that the superconducting film is converted from a superconducting state to a normal state.

10. The method for measuring the physical parameters of a superconducting thin film according to claim 9, characterized in that: The monitoring of the resistance of the superconducting film comprises: Applying a Hall current between the first current electrode and the second current electrode, obtaining a Hall voltage between the first Hall electrode and the second Hall electrode, and calculating the Hall resistance of the superconducting film; Alternatively, an ohmic current is applied between the first current electrode and the first Hall electrode, an ohmic voltage is obtained between the second current electrode and the second Hall electrode, and the ohmic resistance of the superconducting film is calculated.

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