Device and method for measuring physical parameters of superconducting thin films

Abstract

The present application provides a device and method for measuring the physical parameters of a superconducting film. The device includes a measuring structure and a magnetic field generator. The measuring 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 plurality of active electrodes include a first current electrode and a second current electrode, a first Hall electrode and a second Hall electrode, which are spaced apart. The first current electrode is arranged in a first edge region, the second current electrode is arranged in a third edge region, the first Hall electrode is arranged in a second edge region, and the second Hall electrode is arranged in a fourth edge region. The mutual inductance coil is located on at least one side of the superconducting film. The magnetic field generator is located outside the cavity. The corresponding carrier concentration and London penetration depth can be controlled and measured in situ, thereby establishing a quantitative law of how the London penetration depth of the superconducting film changes with the carrier concentration.

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 thin film. Background Art

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

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

[0004] The measuring structure includes 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 includes 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 between them; the plurality of active electrodes are located on the surface of the superconducting film away from the bottom surface of the cavity, and the plurality of active electrodes include 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 includes a first edge region, a second edge region, and 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 along a first direction, the second edge region and the fourth edge region are arranged opposite to each other and both extend along a second direction, 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 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 microns 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 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 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.

[0013] In some embodiments, the magnetic field generator includes a Helmholtz coil assembly, and the Helmholtz coil assembly 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 method includes:

[0015] 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 thin 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 the 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 induction coil to apply a mutual induction magnetic field to the superconducting film and obtaining a mutual induction 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 in the magnetic field inside the superconducting thin film is performed after the step of obtaining the Hall voltage between the first Hall electrode and the second Hall electrode. 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 in the magnetic field inside the superconducting thin film, the measurement method further includes: cooling the superconducting thin film while monitoring the resistance of the superconducting thin film until the resistance of the superconducting thin film suddenly changes to zero, thereby determining that the superconducting thin film has converted to a superconducting state;

[0019] or,

[0020] The step of obtaining the mutual inductance signal generated by the change in 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 in the magnetic field inside the superconducting film, the measurement method further includes: cooling the superconducting film while monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly becomes zero, thereby determining that the superconducting film has switched to a superconducting state; after the step of obtaining the mutual inductance signal generated by the change in 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 while monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly becomes greater than zero, thereby determining that the superconducting film has switched from a superconducting state to a normal state.

[0021] In some embodiments, monitoring the resistance of the superconducting thin 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 a 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 a first current electrode and a 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 is obtained by connecting an external voltmeter to the first Hall electrode and the second Hall electrode, and the Hall resistance of the superconducting film is 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 in situ controlled and measured at different doping levels to obtain the corresponding carrier concentration and London penetration depth, thereby establishing a quantitative law of how the London penetration depth of the superconducting film changes with the change of carrier concentration.

[0026] Additional aspects and advantages of the present application will be given in part in the following description, which will become apparent from the following description, or will be learned through 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 FIG2 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 FIG2 is a schematic diagram showing the distribution structure 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 measurement structure is 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 describes in detail 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 of the following embodiments can complement or be combined with each other.

[0037] Although terms such as "first," "second," etc. may be used to describe various components, such components are not limited by the above terms. These terms are used only to distinguish one component from another and should not be understood to indicate or imply relative importance or implicitly indicate the number of technical features indicated. Thus, a feature 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, "plurality" means 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 that are mutually perpendicular to each other on a horizontal plane, and z can represent a vertical direction.

[0039] The embodiment of the present application provides a device for measuring the physical parameters of a superconducting thin 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 be filled with 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 surface 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 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 the change of 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 a first current electrode and a 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 is obtained by connecting an external voltmeter to the first Hall electrode and the second Hall electrode, and the Hall resistance of the superconducting film is 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 in situ controlled and measured at different doping levels to obtain the corresponding carrier concentration and London penetration depth, thereby establishing a quantitative law of how the London penetration depth of the superconducting film changes with the change of 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 it. 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 induction magnetic field. The mutual induction 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 of the mutual induction magnetic field ranges from 1×10 -3 ~1×10 -2 G (Gaussian).

[0044] In some embodiments, as Figure 1 As shown, the magnetic field generator includes a Helmholtz coil group, which includes a first Helmholtz coil and a second Helmholtz coil, which are 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, as Figure 2 As shown, the mutual induction coil includes a driving coil and a receiving coil, which are distributed on opposite sides of the superconducting film. The driving coil and the receiving coil each include a pair of coils wound in opposite directions and connected in series. The mutual induction coils constitute a transmission mutual induction coil.

[0046] In some embodiments, as Figure 3 As shown, the mutual induction coils include a drive coil and a receiver coil, both located on the same side of the superconducting film. Their axes coincide, and the receiver coils are symmetrically located on either side of the drive coil. The receiver coils comprise a pair of coils wound in opposite directions and connected in series. These mutual induction coils form a reflective mutual induction coil.

[0047] In some embodiments, as 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 spaced apart and distributed around the four sides of the square. Figure 2 or Figure 3 As shown, when the ions in the ionic liquid are driven to be doped into the superconducting thin 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 via leads, and the magnitude of the control voltage can be adjusted and the on and off of the control voltage can be controlled via electrical connectors to achieve control of the doping level of the ionic liquid into the superconducting thin film. In some embodiments, the first current electrode, the second current electrode, the first Hall electrode, and the second Hall electrode of the multiple 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. Because the active electrodes are spaced apart at all sides, the doping level of the ions in each part of the superconducting thin film is relatively uniform during the doping (ion implantation) process, which can improve the accuracy of the measurement results.

[0048] In some embodiments, the active electrode is made of metal. Preferably, the active electrode is made of gold.

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

[0050] In some embodiments, as Figure 5 As shown, 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. This prevents the Hall current from diverging rather than flowing in a straight line due to the current electrode being too short. Preferably, the length x1 of the first current electrode in the first direction x is equal to the first length l1. This ensures that when a constant current is applied between the first and second current electrodes, the current flows as straightly as possible in the second direction y, thereby improving the accuracy of the Hall resistance measurement results of the superconducting film.

[0051] In some embodiments, as 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 half of the second length l2 and less than or equal to the second length l2. The beneficial effects are similar to those of the above embodiment.

[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. Furthermore, when the surface of the superconducting thin film away from the cavity bottom 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, which is greater than or equal to 5 mm. 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. In this embodiment, when the length x3 of the first Hall electrode in the second direction y is greater than or equal to 500 microns, it facilitates connecting an external lead of the first Hall electrode to a voltmeter for measuring the Hall voltage of the superconducting thin 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, it prevents current shunting between the first and second Hall electrodes from affecting the distribution and flow of current in the first direction x.

[0054] In some embodiments, a 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 a 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 similar to those of the aforementioned embodiment.

[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, combined 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 accommodating 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 accommodating 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 housing and top cover are connected by screws, a portion of the housing opening is not covered by the top cover, forming a gap. When measuring the Hall resistance of the superconducting film, leads can be extended from the active electrode surface within the cavity and passed through the gap to connect to an external measuring instrument or circuit structure. This facilitates measurement and, compared to extending leads from the side, routing them from the top avoids the risk of ionic liquid leakage caused by side leads.

[0058] In some embodiments, as 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 receiving groove.

[0059] In this embodiment, the top cover is designed to have a plurality of branch portions, each branch portion can expose a portion of the opening of the receiving groove (ie Figure 7 The gap in the middle) can also improve the stability and supporting capacity of the top cover structure. This allows for the top cover coil holder to be further provided on the main body to accommodate and support the drive 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, as Figure 6 and Figure 7 As shown, in this embodiment, when a transmissive mutual inductance coil is used, the top cover is provided with a top cover coil holder, and the receiving slot is provided with a receiving slot coil holder. The driving coil is housed in the top cover coil holder, and the receiving coil is housed in the receiving slot coil holder. Furthermore, in other embodiments, the driving coil is housed in the receiving coil holder, and the receiving coil is housed in the top cover coil holder.

[0062] In some embodiments, as 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, as Figure 6 、 Figure 7 or Figure 8As shown, the main body is equipped with multiple pins. Leads from the active / control electrodes on the superconducting film can be connected to the pins and fixed, then connected to an external measuring instrument or circuit structure. The pins secure the leads, reducing the risk of lead position deviation or electrical connection failure with the superconducting film. Furthermore, the pins can be designed with metal materials to improve the thermal conductivity of the measurement structure.

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

[0065] In some embodiments, as Figure 2 As shown, the cavity includes a central region and an edge region surrounding the central region. The edge region is deeper than the central region, and the control electrodes are located in the edge region and surround the central region. This increases the contact area between the control electrodes and the ionic liquid while reducing the relative distance between the drive coil and the receiving coil. This improves the efficiency of ion implantation into the superconducting film and increases the strength of the mutual induction signal.

[0066] In some embodiments, the base / top cover / screws of the present application include insulating materials, which can reduce signal interference with the mutual inductance signal compared to metal materials and improve the measurement accuracy of the mutual inductance signal. In one example, the base and 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 thin 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 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 to obtain 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 provided 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 voltage. 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, 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 how the parameter changes with the doping degree.

[0071] It should be noted that when the superconducting film is in a normal state, that is, the Hall resistance / Ohmic resistance of the superconducting film is not zero, in contrast, when the superconducting film is in a superconducting state, the Hall resistance / Ohmic 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 control magnetic field generator is Z The magnetic induction intensity is approximately 2 T (Tesla). Furthermore, in this embodiment, a gradually changing magnetic field (sweeping field) can be applied to the superconducting film, with the magnetic field varying from -2 T to 2 T. This can further determine the slope K of the Hall resistance as it changes with the magnetic field, and the carrier concentration can be calculated using the K value in conjunction with a formula.

[0073] In some embodiments, after step 100, the measurement 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 adjust the carrier concentration corresponding to different doping levels of the superconducting film by controlling the regulation voltage, 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 control 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 drops to zero, thereby determining that the superconducting film has switched to a superconducting state.

[0080] In this embodiment, when the resistance of the superconducting film suddenly changes to zero, it indicates that the temperature of the superconducting film has reached the critical temperature. At this time, the superconducting film has 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, 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.

[0082] Since the solidification temperature of the ionic liquid is generally higher than the critical temperature of the superconducting film, in this embodiment, during the cooling process of the ionic liquid, when the temperature drops to the solidification temperature of the ionic liquid, the ionic liquid changes from a liquid state to a solidified state. At this time, ion injection into the ionic liquid stops, and the ion doping level of the superconducting film can be fixed at the time of solidification. The temperature is then continued to be lowered until the temperature of the superconducting film falls below the critical temperature, at which point the resistance of the superconducting film suddenly drops to zero. At this point, a mutual induction magnetic field can be applied to the superconducting film via a mutual induction coil to measure the London penetration depth of the superconducting film. Since the ion doping level of the superconducting film is fixed during measurement, the problem of the doping level still changing during the measurement process, which could lead to an inaccurate correspondence between the measured London penetration depth values, can be avoided. This can improve the accuracy of the London penetration depth measurement results.

[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 solid state.

[0084] In this embodiment, before measuring the Hall resistance of the superconducting film in step 200, the ionic liquid is preliminarily changed from a liquid state to a solidified state. This allows the ion doping level of the superconducting film to 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 below 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 level of the superconducting film is fixed. This can avoid the problem that the doping level is still changing during the measurement process, resulting in the measured Hall resistance value not being accurately corresponding. This can improve the accuracy of the Hall resistance measurement results. It can further improve the accuracy of the carrier concentration measurement results of the superconducting film.

[0085] In some embodiments, the critical temperature of the superconducting thin 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 drops to zero, thereby determining that the superconducting film has 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 simultaneously monitor the resistance of the superconducting film until the resistance of the superconducting film suddenly changes to be greater than zero, thereby 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 drops to zero, it means that the temperature of the superconducting film has dropped below the critical temperature. At this time, the superconducting film changes from the normal state to the 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 cause the superconducting film to transition from a superconducting state to a normal state. Thus, this embodiment can measure the Hall resistance of the superconducting film and further determine the carrier concentration of the superconducting film when the temperature of the superconducting film is below the critical temperature.

[0088] In some embodiments, the critical magnetic field of the superconducting film has a magnetic induction intensity ranging 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 below the critical temperature. The technical features and beneficial effects of this embodiment are the same as those of step 400, and are not further described here.

[0090] In some embodiments, monitoring the resistance of the superconducting thin 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] This embodiment can determine whether the superconducting film is in a normal state or a superconducting state by online monitoring of the ohmic resistance. This embodiment does not require applying 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 superconducting film can be monitored to determine whether the superconducting film is in the normal state or the superconducting state by monitoring the mutual inductance signal of the superconducting film. When the mutual inductance signal of the superconducting film is large, the superconducting film is in the normal state. When 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 has changed from the normal state to the superconducting state.

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

Claims

1. A device for measuring the physical parameters of a superconducting thin film, characterized in that: include: The measuring structure includes 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 includes 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 between them; the plurality of active electrodes are located on the surface of the superconducting film away from the bottom surface of the cavity, and the plurality of active electrodes include 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 includes a first edge region, a second edge region, and 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 along a first direction, the second edge region and the fourth edge region are arranged opposite to each other and both extend along a second direction, 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 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, wherein: 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, wherein: The main body also includes a base and a top cover that are detachably connected. The base is provided with a receiving groove, and 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 measurement structure also includes a lead wire, which is connected to the active electrode and passes through the area of ​​the opening of the receiving groove 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 the interval 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, wherein: 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 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 includes: 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 thin 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 the 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 includes: when the superconducting film is in a superconducting state, driving the mutual induction coil to apply a mutual induction magnetic field to the superconducting film and obtaining a mutual induction 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 in the magnetic field inside the superconducting thin film is performed after the step of obtaining the Hall voltage between the first Hall electrode and the second Hall electrode. 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 in the magnetic field inside the superconducting thin film, the measurement method further includes: cooling the superconducting thin film while monitoring the resistance of the superconducting thin film until the resistance of the superconducting thin film suddenly changes to zero, thereby determining that the superconducting thin film has converted to a superconducting state; or, The step of obtaining the mutual inductance signal generated by the change in 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 in the magnetic field inside the superconducting film, the measurement method further includes: cooling the superconducting film while monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly becomes zero, thereby determining that the superconducting film has switched to a superconducting state; after the step of obtaining the mutual inductance signal generated by the change in 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 while monitoring the resistance of the superconducting film until the resistance of the superconducting film suddenly becomes greater than zero, thereby determining that the superconducting film has switched 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 thin 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 a 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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