JPH06314800A - Electron-wave interference element - Google Patents

Abstract

PURPOSE:To make such characteristics of an electron-wave interference element as a magneto resistive oscillation appear clearly while suppressing the problems of a universal conductivity fluctuation and the non-locality of a conductivity which are the proper ones to the electron-wave interference element. CONSTITUTION:Between terminals 11, 12, electron-wave interference elements 13 are arranged in the form of a lattice at a spatial period not longer than the phase interference length relative to them, and the interference elements are connected by conduction paths 14 each other. As the constituent ring of the interference element and as the conduction path whereby the two interference elements are connected, a two-dimensional electron gas generated in the interface of a GaAs-AlGaAs heterostructure is used in both cases. When the magneto resistive characteristic at 1.5K of the interference element is taken up, the oscillation generated by Aharanov-Bohm effect can be observed clearly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron wave interference device having an electron quantum interference effect as a principle of operation.

[0002]

2. Description of the Related Art Device characteristics are greatly affected by miniaturization of electronic devices. One reason for this is that quantum mechanical effects that can be almost ignored in macroscopic systems appear in microscopic systems. In particular, when the typical dimension of the device is about the phase interference length or less, the quantum interference effect of conduction electrons becomes remarkable. This effect greatly affects the characteristics of the device. In recent years, many electron wave interference devices have been proposed which positively use this quantum interference effect. Here, a typical one of them will be described.

First, an element using the Aharano-Fouboume effect will be described. From a quantum mechanical point of view, electrons have the property of waves. The Ahalano-Fouboom effect indicates that the phase of the electron wave is modulated by the magnetic field and electric field, and that the modulation state can be observed as an interference phenomenon of the electron wave. This effect is based on Y. Aharono
v) and Baum (D. Bohm) are published in Physical Review Magazine (Phys. Rev., 1959, Vol. 115,
P. 485) presented as a theory for electrons flying in free space.

A similar effect occurs for conduction electrons in solids, as shown by RA Webb et al. In Physical Review Letters (Phys. Re).
v. Lett. , 1985, Vol. 54, P.I. 269
Experimentally shown in 6). The structure of the device they used in the experiment is shown in FIG. Since this element is intended for conductivity modulation by a magnetic field, it is named a magnetic field modulation type Ahalano-Fouboume effect element. This element comprises a ring 43 and two terminals 41, 42. Webb et al., Si ₃
A pattern was formed by contamination with a scanning transmission electron microscope on the Au thin film vapor-deposited on N ₄ , and ion milling was performed by using the pattern as a mask to form an Ahalano-Fouboume effect element. An element having a similar structure is disclosed in Physical Review Letter (Phys. Rev. Lett., 1) by G. Timp et al.
987, Vol. 58, P.P. 2814), it was also made of a GaAs-AlGaAs heterostructure semiconductor, and its operation has been confirmed.

FIG. 4 shows the operation of the Aharano-Fouboume effect element.
Will be explained. The electrons that have entered the ring 43 from the terminal 41 along the electron orbit 44a are separated into two at the branch point of the ring 33, pass through either the electron orbit 44b or 44c, and join again at the other terminal 42, It goes out along the electron orbit 44d. When the circumference of the ring is equal to or less than the phase interference length, the electrons passing through the two paths interfere with each other at the confluence. The conductivity of the element changes depending on the state of this interference. The interference state is determined by the phase difference at the confluence of the electron trajectories 44b and 44c. The phase difference changes due to the magnetic field penetrating the ring. The phase difference is given by θ = θ ₀ + 2πeBS / h. Here, θ ₀ is the initial phase difference, B is the magnetic field, and S is the area surrounded by the ring. Due to the change in the phase difference due to the magnetic field, the interference state at the confluence changes periodically, which appears as a periodic change in the conductivity of the device.

Next, the electric field modulation type Ahalano-Fouboume effect element will be described. The Aharano-Fouboume effect is also caused by an electric field. As shown in FIG. 5, the gate electrode 54 is installed so that the electric field of one part of the ring 53 is different from that of the other. Also in this element, when the circumference of the ring is equal to or less than the phase interference length, the same interference as in the magnetic field modulation type Ahalano-Fouboum effect element occurs. Two paths 55b,
The phase difference between 55c is changed by the electric field formed by the gate electrode 54. The phase difference at the confluence of the electron trajectories 55b and 55c is given by θ = θ ₀ + 2πeψL / v _F. Here, θ ₀ is the initial phase, ψ is the electric field, L is the length of the gate electrode along the ring, and v _F is the Fermi velocity of the electron. In this electric field modulation type Ahalano-Fouboume effect element, the conductivity periodically oscillates with respect to the electric field of the gate electrode. The basic operation of this device was confirmed by Washburn et al. In Physical Review Letter (Phys. Rev. Let).
t. , 1987, Vol. 59, P.I. 1791).

Another example of the device using the quantum interference effect is shown in FIG.
Will be explained. This is called a stub structure element.
This has a structure in which a stub 62 is connected to the conduction path 61. The electrical length of the stub 62 can be controlled by the gate electrode 63 provided in contact with the end of the stub 62. The stub 62 functions as a resonance box for electron waves. When the length of the stub changes, the resonance state of the electron orbit 64b changes, and the conductivity of the conduction path 61 changes due to the change.
Therefore, the conductivity can be controlled by the gate electrode 63.

[0008]

[Problems to be Solved by the Invention] As described above,
Many devices using the quantum interference effect of electrons are still proposed as devices having a new operation principle, which positively utilize the properties of electrons as waves. However, the miniaturization of the device causes another problem, which may impair its characteristics. Typical examples are universal conductivity fluctuations and conductivity nonlocality.

Universal conductivity fluctuation is also a typical quantum interference phenomenon occurring in a fine system. This phenomenon is described by CP Umbach et al. In Physical Review (Phys. Rev., 1984, Vol. 3).
0, P. 4048). This phenomenon mainly appears in the conductivity of pseudo one-dimensional thin wires. The characteristic of this phenomenon is that its conductivity fluctuates even in quasi-one-dimensional thin wires having the same structure, and the fluctuation order is e ² / h.
It is that. The cause of the fluctuation is the dispersion of impurities and the fluctuation of the slight geometrical structure of the device. What is important is that the degree of fluctuation is determined only by the natural constant, not by the value specific to the substance. This universal conductivity fluctuation is also observed in the response of conductivity to an external field such as a magnetic field. Since the ring forming the Aharano-Fouboume effect element generally uses a pseudo one-dimensional thin wire, the influence of this fluctuation occurs as noise for vibration.

The non-locality of conductivity will also be described. This means that even if a structure that is considered not to directly contribute to conduction is added to the element, the influence is reflected in the conductivity. This will be described with reference to FIG. FIG. 7A shows an example of measuring the resistance value of a thin wire by the four-terminal measuring method. In order to measure the thin wire 75, generally, for example, the terminals 71 and 73 are used as current terminals, and a constant current is flown therebetween, and the voltage drop between the terminals 72 and 74 is measured to measure the thin wire 75.
Get the resistance value of. When such a measuring method is adopted, it is considered that it does not depend on the resistance value or the geometric structure of the terminals 71 to 74. However, a ring 76 is added to this as shown in FIG. Then, the magnetic field resistance of this thin wire is observed with an oscillating component that was not seen in the case without the ring. Although the position where the ring is attached does not seem to directly affect the conductivity, the effect is observed. It is considered that this is because the phase interference length is larger than the element size.

As a simple method for avoiding the problems of universal conductivity fluctuation and conductivity non-locality, a method of connecting electron wave interference elements in series or in parallel and averaging variations in element characteristics can be considered. In this regard, C.I. P. Um
bach et al., Physical Review Letter Magazine (Phy
s. Rev. Lett. , 1986, Vol. 56,
P. 386), a magnetoresistive vibration when a plurality of Ahalano-Fouboume effect elements are connected in series is reported. They connected the rings made of Ag to each other in series so that they were not affected by the interference effect (about 2 μm), and evaluated the vibration strength with respect to the number of rings. As a result, it was found that the magnetoresistive vibration due to the Aharano-Fouboume effect decreases with the increase in the number of rings.
It is an object of the present invention to provide an element capable of suppressing a universal conductivity fluctuation and conductivity nonlocality and obtaining a clear Ahalano-Fouboum oscillation.

[0012]

The present invention provides an electron wave interference element arranged with a period of about the phase interference length or less.

[0013]

The present inventor arranged individual electron wave interference elements regularly, and evaluated changes in element characteristics due to the arrangement period. As a result, it was found that the characteristics generated by the individual electron wave interference elements disappeared in the case of any structure of the element when the period was longer than the phase interference length. But,
It was found that the conductivity modulation appears clearly and the universal conductivity fluctuation is suppressed when the period is about the phase interference length or less.

At present, the results of this experiment cannot be explained. However, the following is supposed. The conductivity of some devices is sensitive to structures within a range of phase interference length. Therefore, when the element is directly installed on the element, the element is affected. However, if these elements are arranged periodically and the size of the arrangement is made sufficiently smaller than the phase interference length, the environment of a certain element becomes the same due to its periodicity, so that the element characteristics become uniform. This kind of speculation is possible, but has not yet been confirmed.

[0015]

FIG. 1 is a diagram showing an embodiment of the present invention. Electron wave interference elements 13 are arranged in a grid pattern between terminals 11 and 12. A conductive path 14 connects between the elements. The elements must be arranged with a period of about the phase interference length or less. A material having a sufficiently long phase interference length is used for the conduction path. In this embodiment, the two-dimensional electron gas generated at the GaAs-AlGaAs heterostructure interface is used for both the ring that constitutes the element and the conduction path that connects the elements. This can be achieved by depositing a high-purity GaAs film on a semi-insulating GaAs substrate and forming an n-type AlGaAs pattern on it. 1
Since the phase interference length of this two-dimensional electron gas in Kelvin is several μm, it is sufficient to set the array period to 1 μm or less. Also, the size of the entire grid array, that is, terminal 1
The distance between 1 and 12 and the array width are set sufficiently larger than the phase interference length.

As the electron wave interference element, a magnetic field control type Ahalano-Fouboom effect element, an electric field control type AHARANO-FOBUM effect element, a stub structure interference element, etc. as shown in FIGS. FIG. 2 shows the case where the magnetic field control type Ahalano-Fouboom effect element 23 is used. This may be a structure in which adjacent rings are connected to each other and a part of the rings are shared as shown in FIG. 3, and the rings also serve as a conduction path. In the case of FIG. 3, since the elements can be arranged closer to each other, the characteristics are further improved.

FIG. 8 shows a magnetoresistive device shown in the element array of FIG. The device is the GaAs-AlGaAs heterostructure described above, and the ring period is 200 nanometers. Figure 8
(A) has shown the measured value of the magnetic resistance in 1.5K and 4.2K, respectively. The measured value at 1.5K is 0.
In the range of 4 to 1 tesla, there is a magnetoresistive vibration with a period of 0.1 tesla. This vibration is sensitive to temperature,
It disappeared at 4.2K. Therefore a measured value of 4.2K is background. Therefore, a value obtained by subtracting that of 4.2 Kelvin from the measured value of 1.5 Kelvin is shown in (b). In (b), the vibration clearly appears. It can be seen that this vibration is due to the Aharano-Fouboume effect, and that the present invention provides a clear AHARANO-Fouboum vibration.

Although the elements are two-dimensionally arranged in the embodiments of FIGS. 1 to 3, they may be arranged in series. Further, for the ring and the conductive path, a wire made of a single crystal of metal such as Cu, Au, Ag may be used.

[0019]

According to the present invention, the device characteristics such as magnetoresistive vibration are not lost, the problems of universal conductivity fluctuation and conductivity nonlocality can be suppressed, and the device characteristics can be clearly expressed.

[Brief description of drawings]

FIG. 1 is a structural diagram of an electron wave interference element according to an embodiment of the present invention.

FIG. 2 is a structural diagram of an electron wave interference element according to another embodiment of the present invention.

FIG. 3 is a structural diagram of an electron wave interference element according to another embodiment of the present invention.

FIG. 4 is a structural diagram of a conventional magnetic field control type Ahalano-Fouboume effect element.

FIG. 5 is a structural diagram of a conventional electric field control type Ahalano-Fouboume effect element.

FIG. 6 is a structural diagram of a conventional stub structure type interference element.

FIG. 7 is a diagram showing non-locality of conductivity. Figure 7 (a)
FIG. 3 is a wiring diagram for measuring the electric resistance of a thin wire. Figure 7
(B) is a wiring diagram when a ring-shaped structure is added to (a).

8 (a) is 1.5K, 4.2K shown by the device of FIG.
FIG. 4B is a diagram showing a change in magnetic resistance in FIG. 4B, and FIG. 6B is a diagram showing a difference between two magnetic resistances in FIG.

[Explanation of symbols]

11, 12, 21, 22, 31, 32, 41, 42, 5
1, 52, 71, 72, 73, 74 Terminal 13 Electron wave interference element 14, 24, 33, 61 Conduction path 23 Magnetic field control type Ahalano-Fouboum effect element 43, 53, 76 Ring 44a, 44b, 44c, 44d, 55a , 55b, 5
5c, 55d, 64a, 64b, 64c Electron orbit 54, 63 Gate electrode 62 Stub 75 Fine wire

Claims (1)

[Claims] 1. A plurality of electron wave interference elements arranged at a period of about the phase interference length or less.