JPS5837704B2 - Superconductor point contact Josephson device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a superconductor point-contact type Josephson element having an L-shaped configuration in which the tip of an acicular superconductor electrode is brought into point contact with a superconductor electrode.

Conventionally, a well-known superconductor point-contact type Josephson element is constructed by forming the free end surface of a superconductor wire 1 into a flat contact surface 2, as shown in FIG.・A superconductor electrode 3 having a configuration of , the tip 5 of the acicular superconductor electrode 7 is in point contact with the contact surface 2 of the superconductor electrode 3.

By the way, the superconductor point contact type Josephson element as shown in FIG. The smaller the contact area (L) where the tip 5 of the needle-like superconductor electrode 7 makes point contact with the electrode 3, the better the characteristics will be.

In this sense, it is said that the superconductor electrode 3 and the acicular superconductor electrode 7 presently exhibit the highest transition temperature.
It is preferable that Nb3Ge be used.

Further, it is preferable that the tip 5 of the needle-like superconductor electrode 7 has an extremely small radius of curvature, such as several μm or less, preferably 1 μm or less.

However, a superconductor made of Nb3Ge can be produced on a substrate by chemical vapor deposition, sputtering, vapor deposition, etc.
Even if it is possible to obtain it in a layered form, it is extremely difficult to obtain it in a linear form as it exhibits the desired high transition temperature, and in fact all of the examples are L.

For this reason, the conventional superconductor point contact type Josephson element having the configuration described above in FIG.
The acicular superconductor electrode 7 is usually made of a superconducting material such as Nb, which exhibits a lower L transition temperature than NbsGe.

In addition, for the needle-like superconductor electrode 7, a superconductor wire made of an L superconductor material that exhibits a lower L transition temperature than Nb3Ge is obtained in advance, and its free ends are etched by mechanical etching or chemical treatment. It is generally assumed that L.L. is obtained by etching processing such as etching, ion etching, etc.
Ta.

Therefore, in the conventional superconductor point-contact type Josephson element described above in FIG.
Since it is a superconductor material, it did not exhibit sufficiently satisfactory characteristics.

Furthermore, since the acicular superconductor electrode 7 is obtained by preparing a superconductor linear body in advance and then etching it, a superconductor point-contact type Josephson element is used. ,
It has drawbacks such as not being easy to manufacture.

For this reason, the present inventors conducted various experiments and found that N b s was deposited on a suitable substrate by chemical vapor deposition.
When a superconductor layer of Ge is deposited and lengthened, its N
A superconductor layer made of b3Ge is obtained as one exhibiting a high L transition temperature, and therefore, the superconductor layer made of Nb3G+ is used as a superconductor layer constituting a superconductor point contact type Josephson element. It was confirmed that it can be used as an electrode.

Moreover, the superconductor layer made of Nb3Ge, which exhibits a high transition temperature, obtained in this way, as shown in FIG.
A large number of needle-shaped bodies made of Nb3Ge are formed on the surface of the L.
The needle-like body consisting of e has a tip of several μm or less, and even 1 μm.
There exists a superconductor layer with an extremely small radius of curvature, such as less than It has also been confirmed that a superconductor point-contact type Josephson element can be constructed with an L-shaped tip as a needle-shaped superconductor electrode.

Furthermore, the surface of the superconductor layer consisting of Nb3Ge, which exhibits a high transition temperature, can be made flat by mechanical or chemical polishing means, so that the surface of the superconductor layer consisting of Nb3Ge, which exhibits a high transition temperature
It has also been confirmed that a superconductor layer made of 3Ge can be used as a superconductor electrode that can be brought into point contact with a needle-shaped superconductor electrode constituting a superconductor point-contact type Josephnon element.

The superconductor layer shown in FIG. 2 is made of a metal material such as Cu, Mo, Ti, etc., which is supported by a jig 12 in the reactor 11, as shown in FIG. A base 13 made of a ceramic material such as alumina is disposed, and the reactor 11 is
Inside, a mixed gas 14 of Nb chloride gas, Ge chloride gas, and H2 gas is set at a flow rate ratio of 2.5 to 3.5, and Nb chloride gas and Ge chloride gas are mixed. The flow rate of the mixed gas with gas is set to 20 to 80 Ct/min,
Further, H2 gas is introduced at a flow rate of 1 to 2 t/min, and a carrier gas consisting of He gas or Ar gas is introduced at a flow rate of 10 to 20 L/min. Heaters placed around 1
5 to a temperature of 850 to 950° C., thereby reducing Nb chloride gas and Ge chloride gas with H2 gas, and depositing Nb3Ge on the surface of the substrate 130.
A superconductor layer 16 consisting of L. An example of a superconductor layer is shown below.

Therefore, we have come to propose a superconductor point contact type Josephson element according to the present invention, and one example thereof is the fourth
As shown in the figure, the appearance has the structure of the conventional superconductor point-contact type Josephnon element described above in FIG. A base wire body 2 made of a metal material such as alumina or a ceramic material such as alumina.
N2 was deposited on the outer surface of No. 2 by the chemical vapor deposition method described above.
A superconductor 23 made of b3Ge is formed, and its end surface 21
is formed on the flat contact surface 24 by mechanical or chemical polishing means, and has a superconductor electrode 25 having a configuration of .

Further, by the chemical vapor deposition method described above, on the outer surface of the base wire body 28 made of the same material as the base wire body 22 described above, the end of which is formed into a needle-like portion 27 having a pointed end 26. The superconductor layer 29 made of Nb3Ge is
6 has a needle-like body having an extremely small radius of curvature of several micrometers or less (L.
As shown in FIG. 2, as the tip 30,
It has an acicular superconductor electrode 31 having a shape of L.

However, on the contact surface 24 of the superconductor electrode 25 mentioned above,
The tips 30 of the acicular superconductor electrodes 31 are in point contact.

In this case, a large number of needle-like bodies are formed on the surface of the superconductor layer 29 on the tip 26 of the base wire 28.
・These are placed on the contact surface 24 of the superconductor electrode 25,
When the superconductor layer 29 is in contact with the superconductor layer 29, one of the plurality of needle-like bodies, especially one with a small radius of curvature and a long protrusion length, is removed by selective etching means for the superconductor layer 29. If the other needle-shaped bodies are removed while leaving , it is good L.

As described above, one example of the structure of the superconductor point-contact type Josephnon element according to the present invention has been clarified.

According to the superconductor point contact type Josephson device according to the present invention having such a configuration, both the superconductor electrode 25 and the acicular superconductor electrode 31 are made of NbsGe, and they have a high transition temperature. It has a temperature.

Further, the tip 30 of the acicular superconductor electrode 31 is connected to the base wire 2
Nb3Ge formed by chemical vapor deposition on 8
Since it is a needle-shaped body made of NbsGe that is placed on the surface of the superconductor layer 29, its tip 30 has an extremely small radius of curvature of several μm or less, and therefore, it is difficult to contact with the superconductor electrode 25. The contact area where the tip 30 of the acicular superconductor electrode 31 makes point contact with the surface 24 is sufficiently small.

Therefore, according to the configuration of the superconductor point-contact type Josephson element according to the present invention described above, if it exhibits sufficiently satisfactory characteristics as a superconductor point-contact type Josephson element, it has a characteristic of 5 degrees Celsius. has.

In addition, since the needle-shaped superconductor electrode can be easily obtained by forming a superconductor layer on a substrate by chemical vapor deposition, it is possible to obtain a superconductor point-contact type Josephnon element. It also has the characteristics of being able to provide the following at a low price.

The above description merely shows an example of the present invention; for example, in the configuration described above in FIG.
7. Therefore, the tip 30 of the acicular superconductor electrode 31 made of Nb3Ge is formed on the flat end surface of the base wire 28. It is also possible to have the same structure as described above, except that the superconductor layer 290 is formed on the surface of the superconductor layer 290 made of Nb3Ge.

In addition, in some cases, the acicular superconductor electrode 31
The configuration described above in FIG. 4 is used, but the superconductor electrode 25 with which the acicular superconductor electrode 31 makes point contact is replaced with a superconductor electrode having the structure described above in FIG. You can also do that.

Various other modifications may be made without departing from the spirit of the invention.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing a conventional superconductor point contact type Josephson device. FIG. 2 is a diagram showing the surface of a superconductor thin layer shown in an electron micrograph for explaining the tip of the needle-like superconductor electrode of the superconductor point-contact type Josephnon element according to the present invention. It is. FIG. 3 is a schematic diagram showing a method of forming a needle-like superconductor electrode of a superconductor point-contact type Josephson device according to the present invention. FIG. 4 is a schematic perspective view showing an example of a superconductor point contact type Josephson device according to the present invention. 21...End face, 22...Base wire body, 2
3...Conductor layer, 24...Contacted surface,
26... Point, 21... Needle-like part, 28
...Base wire body, 29 ... Superconductor layer,
30...Tip, 31...Acicular superconductor electrode.

Claims (1)

[Claims] 1. In a superconductor point-contact type Josephson element having an L configuration in which the tip of the acicular superconductor electrode is brought into point contact with the superconductor electrode (the tip of the acicular superconductor electrode is was formed by chemical vapor deposition on a substrate.
A superconductor point-contact type Josephson device characterized by a needle-shaped body made of NbaGe on the surface of a superconductor layer made of.