JPS60177691A - Superconductive multi-terminal element - Google Patents

Abstract

PURPOSE:To enable an operation which realizes gain, by producing spatial non- uniformity in superconductivity and by controlling electric current passing through a superconductor with a weak current supplied via a Josephson junction. CONSTITUTION:A Josephson junction is constituted with a conductor layer 7 on the supply side of a tunnel of the Josephson junction, an insulation film 6 and a layer 5 provided by diffusing a magnetic impurity in a superconductor layer 4. In the superconductors in this structure, a magnetic impurity is diffused from the face of the layer 7 such that the concentration becomes non-uniform in the direction of thickness, whereby spatial ununiformity in superconductivity is produced artifitially. Accordingly, when a voltage is applied between terminals C and B and electric current is supplied from the layer 7, the layer 5 and a part of the layer 4 become a normal conductor, and thus the part with superconductivity is reduced. This causes a potential difference between terminals A and B to be switched between zero and a value corresponding to that of bias current by supplying weak current from the terminal C. Further, gain is produced in this operation since the control current from the terminal C is smaller than the current between the terminals A and C.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention utilizes the broximity (proximity) effect in superconductivity to provide gain, dramatically improve frequency characteristics, and improve the performance of electronic circuits. This invention relates to superconducting multi-terminal devices used in confectionery.

[Prior art]

Figure 1 shows the structure of a conventional Josephson element that mainly constitutes the minimum unit used in previous logic works. This is a terminal drawn out from the superconductor +11. This device has two superconductors +11 and +31 with an extremely thin insulating film sandwiched between them, and has two terminals x and YIH! The conduction of electrons (
This is realized by the tunnel effect (as a pair of Coopers).

Next, the operation of this element will be explained. Figure 2 is a diagram showing the voltage/current characteristics of this Josephson element, where the horizontal axis vx-y is the voltage between terminals X and Y, and the vertical axis Ix-y is the voltage of this element flowing between terminals X and Y. It is an electric current. IC consists of superconductor (11, +31) and insulating film (2) materials and insulating film (
The current value, Vc, determined by the thickness of 2) is (Δ1+Δ3)/
The voltage value is equal to e. However, △1 and △3Iri
Figure 2 shows the gap energy e and electron charge at absolute zero temperature (o'K) VC for superconductors (1) and (3), respectively.
3) The lower transition temperature Ttra of the superconducting transition temperatures
n is the characteristic at a sufficiently lower temperature.

As shown in FIG. 2, the switching elements are:
A quasi-particle tunnel state with a voltage value of Vc or more and a quasi-pressure value of Vc
This method utilizes the following rapid transition between the tunnel state of a pair of superconducting turbines.

However, since such a conventional two-terminal device is constructed as described above, it has the disadvantage that it can only operate with limited efficiency as an element that operates in a trivial manner.

[Summary of the invention]

This development (7) was made in view of the above points, and one superconductor constituting the Josephson junction diffuses magnetic impurities from one surface to increase the impurity concentration in the thickness direction. operation with gain by artificially creating spatial non-uniformity in the superconducting properties and making it possible to control it with a weak current injected from the other conductor side of the Josephson junction. The present invention provides a superconducting multi-terminal element that performs the following steps.

[Embodiments of the invention]

Figure 3 is a cross-sectional view of the entire structure of Example (7) of this invention, in which (4) is a superconductor layer, +51 is a diffusion layer in which magnetic impurities are diffused in the superconductor layer (4), t6Hd insulating film, (7)
is a superconductor or a normal conductive metal layer, (8) is a magnetic impurity diffusion interface, A and B are terminals f″ drawn out from both end faces of the superconductor layer (4), and C is a superconductor or a normal conductor. This is a terminal drawn out from the upper surface of the metal layer (7).Note that it is shown as a plane to make the magnetic impurity diffusion interface clear.

In this example, layer (7), insulating film (6) and layer i51
form a Josephson junction. Layer (51 and layer: 4
) are structural parameters that determine the characteristics of the current flowing between terminals A and B. The current flowing between terminals A and B is increased by 1 lil due to the current injected from terminal C.
The thickness of the insulating film (6) is also a critical structural parameter because it is controlled. Of course, terminals A, B, and C are each connected to an external circuit as appropriate.

Now, if we keep the temperature low enough to sufficiently develop the order parameter of superconductivity (order parameter: variable that affects the number of degrees of the Cooper pair and its phase) in the material of layer (4), the layer (
Since layer 51 has a lower transition temperature than layer (4), it is thought that the order parameter has not yet grown sufficiently or that it does not undergo supertransition and remains in the conventional phase. However, the gloximity effect (proximity effect)
Diffusion interface virtually illustrated by a phenomenon called
can be a discontinuous surface of order parameters, the layer (4
) is in the layer (51), and the quasiparticle in the layer (51 is in the layer (
4) respectively.

As a result, the order parameter changes spatially from layer number + 41 toward layer (5), and a situation appears in which the superconducting properties are spatially non-uniformly distributed. There is. In this example, considering the above-mentioned situation, the insulating film of layer (5) (the part near 61) has a small order parameter, easily regains normal conductivity by a weak stimulus from the outside, and becomes super conductive. This pushes the conductivity back towards the layer (4).Therefore, by applying a voltage between terminals 0 and B, a current (in the form of a Cooper pair or a quasiparticle) is injected from the layer (7). As a result, part of the layer (51 and layer 4) becomes a normal conductor, and the superconducting part is compressed.
, B reduces the critical current for superconducting to normal conduction transition with respect to the current flowing between B.

Figure 4 is a diagram showing the voltage/current characteristics between terminals A and B using the supplied current from terminal C as a parameter in this embodiment. When no current is injected from terminal C, the critical current shows IC1, showing the characteristics shown in the diagram (a).However, when current is injected from terminal C, the critical current becomes IC2 for the reason described above, and the critical current shows IC2, as shown in the diagram. (b) becomes the characteristic. Therefore,
Assuming that the current is initially biased toward the current shown in (c) in the figure, the operating point shifts to the point shown in the figure by injecting a weak current from terminal C, and the Vi potential difference between terminals A and B is VB. occurs. This means that by injecting a weak current from terminal C, the potential difference between terminals A and B is zero (1°O゛ in the binary function) and the potential difference VB (°“1pa in the binary function). Moreover, this operation is accompanied by a gain because the control current from terminal C is smaller than the current flowing between terminals A and B.

In the above embodiments, the diffusion interface of the magnetic impurity was made flat, but the shape of this interface may also be other than a flat surface, such as lff1f41. The IJ control can be controlled by changing the thickness of the layer (51).

In addition, similar effects can be expected for the terminal fully drawn out from the layer (6:), the voltage between this pane and the terminal A, and the sneak current characteristics.

〔Effect of the invention〕

As explained above, in this invention, magnetic impurities are diffused from one main surface of one of the superconductors forming the Josephson junction to create a structure in which the impurity concentration is non-uniform in the thickness direction. By forming the spatial non-uniformity of m1 production margin is large,
Crystal speed disturbance can also be achieved.

[Brief explanation of drawings]

Figure 1 is a perspective view showing the structure of a conventional Josephson element.
Fig. 2 is a diagram showing the 70' voltage/current characteristics, Fig. 3 is a sectional view showing the structure of one embodiment of this invention, and Fig. 4 is a diagram showing the voltage and voltage characteristics for explaining the operation of this embodiment.・This is a current characteristic diagram. In the figure, a j41ij superconductor layer, (51 magnetic impurity diffusion layer, (61 an insulating film, (7) a conductor layer on the tunnel injection side of the Josephson junction made of superconductor or normal metal, +81 Vi diffusion Interface, A, B, OVi terminals. Agent Masuo Oiwa Figure 1 Figure 2 VCVX-Y Figure 3 Figure 4 vc2 VB VcIS-B

Claims (3)

[Claims] (1) Diffusion of magnetic impurities from one main surface of one of the superconducting bodies constituting the Josephson junction creates a structure in which the impurity acidity is non-uniform in the thickness direction, thereby causing spatial inconsistencies in the superconducting properties. uniformity, and the current flowing through the superconductor is controlled by a tunnel current injected by tunneling effect through the Josephson junction from the other conductor side forming the Josephson junction. A superconducting multi-terminal device. (2) The superconducting multi-terminal element according to claim 1, characterized in that a normal conductive metal is used for the conductor on the tunnel sleep flow injection side of the Josephson hair clip. (3) The method according to claim 1, characterized in that the conductor on the tunneling current injection side of the Josephson junction uses a superconductor having a different superconducting transition temperature from the superconductor on the injection target side. Superconducting multi-terminal device.