JPH0513831A - Superconducting element - Google Patents

Abstract

PURPOSE:To obtain a superconducting element applicable in a wide field in a structure entirely different from that of a conventional Josephson element or the like by a method wherein two kinds or more of superconductors, whose cohesive energy losses per unit length of the conductors are different from each other, are jointed together. CONSTITUTION:Two superconductors 1a and 1b, whose cohesive energy losses per unit length of the superconductors at the time when a magnetic flux intrudes in the superconductors and the superconductive states of the superconductors are destructed are different from each other, are jointed together. Assuming that a current flows in the direction shown by an arrow 2 and the magnetic flux is faced upward as show by an arrow 3, a Lorentz's force is generated between the current, which is made to flow through the superconductors, and the magnetic flux and the magnetic flux inclines to move in the direction shown by an arrow 4. That is, the direction is the superconductor 1a the superconductor 1b. Here, when the cohesive energy loss per unit length of the superconductor 1a is assumed to be smaller than that of the superconductor 1b, the magnetic flux in the superconductor 1a is pin-locked in the interface between the superconductors 1a and 1b, the magnetic flux to intrude from the side of the superconductor 1a can not be moved to the side of the superconductor 1b, the superconductive state of the superconductor 1a is held up to a certain value of a critical current and a voltage is not generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting element such as a magnetic sensor, a magnetic flux trap element and a switching element which can be used in a wide range of applications.

[0002]

2. Description of the Related Art Research is being conducted to apply a metal superconductor or an oxide superconductor having a critical temperature Tc of 77K or higher, such as Y, Bi, or Ti, as an element.

For example, research has been conducted on a highly sensitive magnetic sensor (SQUID), a switching element, a superconducting transistor, etc., which utilizes a Josephson junction of a superconductor.

[0004]

SUMMARY OF THE INVENTION The present invention is intended to provide a superconducting element having a structure which is completely different from that of the conventional Josephson element or the like and which can be applied in a wide variety of fields.

[0005]

The present invention provides a first superconductor layer and a second superconductor layer provided in contact with the first superconductor layer and having a superconducting property different from that of the first superconductor layer. , An electrode formed so as to flow a current in a direction parallel to a bonding interface between the first superconducting layer and the second superconducting layer, the electrode being parallel to the bonding interface and perpendicular to the current direction. In the superconducting element, the junction interface serves as a barrier only when the magnetic flux moves from the first superconducting layer to the second superconducting layer or only in the opposite direction. is there.

The present invention also provides a first superconductor layer, a second superconductor layer provided in contact with the first superconductor layer, and a bonding interface between the first superconductor layer and the second superconductor layer. And an electrode formed so that a current flows in a direction parallel to the first superconducting layer and the second superconducting layer, a magnetic field in a direction parallel to the junction interface and perpendicular to the current direction is provided. Condensation energy loss ε when applied (where ε is the condensation energy loss per unit length when the magnetic flux penetrates and the superconducting state is destroyed, and ε = (B _c ² / 2μ ₀ ) ・ πξ ²
It is represented by. Where B _c is the thermodynamic critical magnetic field, μ
_The superconducting element is characterized in that ₀ is the magnetic permeability of the vacuum and ξ is the coherence length).

That is, the present invention relates to a case where two or more kinds of superconductors having different condensation energy loss per unit length when magnetic flux penetrates into the superconductor to destroy the superconducting state are joined. It utilizes the physical properties of the interface.

In general, a superconductor is in an energy stable state in the superconducting state as much as the superconducting energy-gap compared to the normal conducting state. When an external magnetic field is applied to the superconductor, the magnetic flux penetrating inside the superconductor exists as a quantized magnetic flux. The radius of this magnetic flux has a spread of about the coherence length. Also,
The superconducting state is broken in the part where the magnetic flux has entered, and the state is in the normal conducting state, and the state is high in terms of energy. When a current is passed through a superconductor in a magnetic field, a Lorentz force is generated between the current flowing in the superconductor and the magnetic flux. If the force to stop the magnetic flux is not working, the magnetic flux starts moving in the superconductor. However, a normal superconductor contains a structure that stops the magnetic flux from moving. That is called "pinning". The pinning effect is due to various defects inevitably contained in the superconductor and the non-superconducting phase. The magnetic flux exists preferentially in these parts and is subject to pinning action. However, the magnetic flux moves if the pinning action is weaker than the Lorentz force generated between the magnetic flux and the current flowing through the superconductor when a current is passed through the superconductor.

Loss ε ₁ of each condensation energy per unit length when magnetic flux penetrates into two superconductors having coherence lengths of ξ ₁ and ξ ₂ to destroy the superconducting state. , Ε ₂ is obtained,

[0010]

[Equation 1]

[0011]

[Equation 2] Becomes In Equations 1 and 2, Bc is the thermodynamic critical magnetic field, μ ₀
Is the vacuum permeability. When two superconductors are in contact with each other, the above energy difference becomes the pinning energy at the boundary. The superconducting element of the present invention utilizes this energy difference. A configuration diagram of the superconducting element of the present invention is shown in FIG. As shown in Fig. 1, two superconductors 1a and 1b, each having different condensation energy loss per unit length when magnetic flux penetrates into the superconductor to destroy the superconducting state, There is. Further, the superconducting element of the present invention has a mechanism in which a current flows in parallel to the interface between the superconductors 1a and 1b. If a current flows in the direction of arrow 2 and the magnetic flux is directed upward as shown by arrow 3, a Lorentz force is generated between the current flowing in the superconductor and the magnetic flux. The magnetic flux receives the Lorentz force in the direction (the direction indicated by arrow 4) taught by the "Fleming's left-hand rule" and tries to move. That is, the superconductor 1a
→ The direction is 1b. Here, when the cohesive energy loss per unit length in the superconductors 1a and 1b is ε _A and ε _B , if ε _A <ε _B , the magnetic flux in the superconductor 1a is at the interface between the superconductors 1a and 1b. Pinned. Therefore, 1
The magnetic flux that has entered from the a side cannot move to the 1b side, and the superconducting state is maintained up to a certain critical current value (current value that generates a force that crosses the interface), and the magnetic flux does not move, so that no voltage is generated.

On the other hand, the direction of current flow is opposite to the direction indicated by arrow 2 in FIG. 1, or the direction of magnetic flux is indicated by arrow 3 in FIG.
If the direction is opposite to the direction of, the direction of the Lorentz force that the magnetic flux receives will be reversed. When the cohesive energy loss per unit length in the superconductors 1a and 1b is ε _A and ε _B , if ε _A <ε _B , the magnetic flux penetrating from the superconductor 1b acts as a pinning action at the interface. Moves easily without receiving. The movement of the magnetic flux causes a voltage to be generated in the superconductor.

As described above, by arranging the interface so that the two types of superconductors having different condensed energy loss (ε) per unit length are parallel to the direction of current flow, the direction of current flow Alternatively, the behavior of the magnetic flux changes with respect to the direction of the magnetic field, which causes the generation and disappearance of voltage,
The signal can be detected.

When the thermodynamic critical magnetic field Bc is the same, the same phenomenon occurs if superconductors having different coherence lengths (ξ) are used. There is a correlation between the thermodynamic critical magnetic field Bc and the coherence length ξ, and the difference in coherence length is
It has almost the same meaning as the difference between cohesive energy per unit length and loss in a superconductor.

In order to effectively exhibit the above operation,
It is desirable to minimize defects and distortion inside the superconductor and to reduce pinning points. This is because if there is a pinning point inside the superconducting material, the movement of the magnetic flux is hindered.

The combination of superconductors is not particularly limited as long as it is a combination of superconductors having different coherence lengths, and a metal-based superconductor having a large coherence length,
A combination of oxide-based superconductors having a short coherence length, or a combination of oxide-based superconductors having different coherence lengths depending on the crystal orientation, that is, C
Examples include combinations in which the axis direction is orthogonal to the boundary. The superconducting element of the present invention can be applied to various elements.

For example, in the superconducting element shown in FIG. 1, the direction of the magnetic field applied to the superconducting element can be detected by changing the direction of the current applied to the element, and it can be used as a magnetic sensor. On the contrary, by changing the direction of the magnetic field applied to the element, the direction of the current flowing through the element can be detected.

Further, it can be applied as a magnetic flux trap element capable of arbitrarily trapping or releasing magnetic flux at the interface of the superconductor by changing the direction of current. In addition, if the magnetic field direction is kept constant, voltages 0 V and aV can be output depending on the current direction, and the device can be applied as a device element such as a switching element. Furthermore, since the direction of the magnetic flux can be detected, it is possible to read the upper and lower directions of the magnetization stored in the perpendicular magnetization film.

As a method of manufacturing the superconducting element of the present invention,
First, laser ablation method, vapor deposition method, sputtering method, C
A VD method or the like is used to form a superconductor layer in which superconductors having different coherence lengths are joined depending on the difference in composition and crystal orientation. FIG. 2 shows an example of a procedure for forming a superconducting layer in which superconductors having different crystal orientations are joined. First, FIG.
As shown in (a), a film 6 oriented in a different orientation from the substrate is formed on the crystal-oriented substrate 5. Next, as shown in FIG. 2B, the film 6 is etched leaving a predetermined size. Then, as shown in FIG. 2C, the superconductor 7 is laminated on the substrate. As a result, the superconductor 7 stacked on the substrate 5
(A) is oriented in the same direction as the substrate 5, and the superconductor 7 (b) laminated on the film 6 is oriented in the same direction as the film 6.
As a result, it is possible to obtain a superconducting layer in which the superconductor alignment films in different directions are in contact with each other at their interfaces. In addition, if necessary, as shown in FIG.
By etching, it is possible to obtain a superconducting layer in which the superconductor alignment films in different directions are in contact with each other at the interface. Also, a method of partially changing the crystal orientation by irradiating with a laser is used.The superconductor is laminated on a substrate on which crystal plates with different orientations are arranged on the substrate on which the superconductor is laminated. Etching method, etc. As described above, the superconducting element of the present invention is obtained by bonding electrodes and the like to the obtained superconducting layer so that a current flows parallel to the interface of the superconductor.

[0020]

EXAMPLES The present invention will be described below with reference to examples.

FIG. 2 shows a schematic view of a method of manufacturing the superconducting layer of the superconducting element of this embodiment. As shown in FIG. 2 (a),
On the SrTiO ₃ substrate 5 oriented in the (001) direction, PrBa ₂ Cu ₃ Oy was formed by an excimer laser ablation method.
The film 6 was formed first. At this time, the substrate temperature is about 650 ° C
And The PrBa ₂ Cu ₃ Oy film 6 had a thickness of about 500 Å and was an a-axis oriented film. Next in FIG.
As shown in (b), the remaining part was etched by ion milling, leaving the rest. Next, as shown in FIG. 2C, the substrate temperature is set to about 800 ° C. and the excimer laser ablation is performed.
The YBa ₂ Cu ₃ Oy film 7 was formed by the ionization method. The film thickness is 2000 angstroms, the YBa ₂ Cu ₃ Oy film 7 (b) on the PrBa ₂ Cu ₃ Oy film 6 exhibits a-axis orientation, and the YBa ₂ Cu ₃ Oy film 7 on the SrTiO ₃ substrate 5 is shown.
(A) showed c-axis orientation. Width 100 in this way
A superconducting layer having a thickness of 500 μm and a length of 500 μm and having an interface between the a-axis alignment film and the c-axis alignment film in the longitudinal direction was prepared. After depositing Au on both ends, electrodes were joined to obtain a superconducting device.

Using the superconducting element obtained by the above method,
The IV characteristic was measured by a 4-terminal method at 7 k. Then 10
A 0 G magnetic field was applied in the direction of the arrow in FIG. As a result, a voltage of 1 μV was generated when a current of 20 mA was applied in the direction of the arrow. Next, the direction of applying the magnetic field is reversed, and I-
The V characteristic was measured. As a result, a voltage of 1 μV was generated at 1 mA. It was possible to detect the difference in the IV characteristics depending on the magnetic field direction.

When the IV characteristic was measured while reversing the direction of the current while keeping the direction of the magnetic field constant in the direction of the arrow in FIG. 1, similarly, the current for generating a voltage of 1 μV was 20 mA and 1 mA. And could detect the difference.
Moreover, these numerical values changed by changing the strength of the magnetic field.

[0024]

As described above, the superconducting device of the present invention is
The configuration is different from the conventional one and can be applied to devices in many fields.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a superconducting element of the present invention.

FIG. 2 is a schematic diagram showing a procedure for joining superconductors.

[Explanation of symbols]

1 (a) Superconductor 1 (b) Superconductor 2 Direction of current flow 3 Magnetic field direction 4 Lorentz force direction 5 substrates 6 Crystal-oriented substrate 7 Superconductor 7 (a) Superconductor 7 (b) Superconductor

Claims (2)

[Claims] 1. A second superconductor layer having superconducting characteristics different from those of the first superconductor layer and the first superconductor layer provided in contact with the first superconductor layer, the first superconductor layer and the second superconductor layer. And an electrode formed so as to flow a current in a direction parallel to the junction interface with the superconductor layer, and a magnetic flux in a direction parallel to the junction interface and perpendicular to the current direction is from the first superconductor layer. Second
2. The superconducting element, wherein the junction interface serves as a barrier only when moving to the superconducting layer or when moving in the opposite direction. 2. A first superconductor layer, a second superconductor layer provided in contact with the first superconductor layer, and a direction parallel to a bonding interface between the first superconductor layer and the second superconductor layer. An electrode formed so that a current flows through the first superconducting layer and the second superconducting layer when a magnetic field in a direction parallel to the junction interface and perpendicular to the current direction is applied. Condensation energy loss ε (where ε is the condensation energy loss per unit length when magnetic flux penetrates and the superconducting state is destroyed, and ε = (B _c ² / 2μ ₀ ) ・ πξ ² It is represented by. Here, B _c is a thermodynamic critical magnetic field, μ ₀ is a magnetic permeability of vacuum, and ξ is a coherence length).