CN206293444U - A kind of single electron spin filter based on quantum dot - Google Patents

Abstract

A kind of single electron spin filter based on quantum dot, chief component is single-electronic transistor, single-electronic transistor has coulomb island, source electrode, drain and gate, quantum dot as single-electronic transistor coulomb island, coulomb island is connected with source electrode and drain electrode with tunneling barrier, and coulomb island is coupled with grid with capacitive form；Single-electronic transistor is placed in vertical magnetic field, and the drain output connection spinning electron reading circuit of single-electronic transistor, spinning electron reading circuit is placed in horizontal variation magnetic field.The method that the utility model is regulated and controled using outside, make the non-polarised electronics of spin by after single-electronic transistor, it is changed into the electronics of spin polarization, and the spin direction of electronics can be judged and be counted, be conducive to that data processing is fast, low in energy consumption, good stability spin electric device design application.

Description

A single-electron spin filter based on quantum dots

technical field

The utility model relates to the field of nanoelectronic devices, single electron spin and electronic technology, in particular to a single electron spin filter based on quantum dots, in particular to a quantum dot plug located in the source-drain bias window Device Design for Spin Filtering by Mann Splitting Energy Levels.

Background technique

Compared with traditional electronic devices, spintronic devices have the advantages of fast data processing speed, low power consumption, and good stability. The spintronic devices that have been successfully developed include giant magnetoresistance, spin valve, magnetic tunnel junction and magnetic random access memory, etc. However, for these spintronic devices based on ferromagnetic metals, it is difficult to develop spin transistors with amplification functions, and it is also difficult to realize the integration with traditional microelectronic devices.

The spin polarizability of spontaneous electrons in semimetals is almost 100%. Therefore, semimetal materials can be used as spin-polarized emission sources to study spin polarization. Common semi-metallic materials are: doped manganese oxide, double perovskite manganese oxide, chromium dioxide, iron oxide and Heussler alloy, etc. However, the Curie temperature of semi-metals is relatively low, and the electron spin polarizability will decrease rapidly with the increase of temperature, these shortcomings greatly reduce the practical application value.

In 1988, J. S. Moodera and others first proposed the concept of spin filtering in tunnel junctions. According to the barrier layer materials used in tunnel junctions, such tunnel junctions can be divided into three types: ferromagnetic tunnel junctions, ferroelectric tunnel junctions and Multiferroic tunnel junctions (including single-phase multiferroic and composite multiferroic tunnel junctions). The ferromagnetic tunnel junction refers to the tunnel junction using ferromagnetic insulating material or semiconductor material as the barrier layer. Its spin polarization comes from the spin filter effect of the ferromagnetic semiconductor barrier. The origin of the spin filter effect of the ferromagnetic tunnel junction is Due to the spin dependence of the height of the ferromagnetic barrier, factors such as the magnetism, height and width of the barrier will also have a certain impact on the filtering effect. A ferroelectric tunnel junction refers to a tunnel junction that uses a ferroelectric insulating material as a barrier layer. The spontaneous polarization of the ferroelectric barrier causes shielding charges to be generated at the interface close to the barrier in the electrode, thereby forming an electrostatic potential, which distorts the energy band in the electrode, that is, the electrons of the two channels of spin up and down pass through the tunnel junction The tunneling probability is different, so the spin filter effect occurs. The spin-filtering effect of the ferroelectric tunnel junction originates from the fact that the effective width of the barrier layer is spin-dependent. The multiferroic tunnel junction is made of a ferromagnetic-ferroelectric multiferroic material with both ferromagnetic and ferroelectric properties as a potential barrier. The two physical mechanisms that produce the spin filtering effect are also possible in such a multiferroic tunnel junction. Simultaneous action in the tunnel junction.

In non-magnetic semiconductors and topological insulators, the spin-orbit interaction of particles can produce spin polarization. The silicene material is similar to the graphene structure, and the edges of its conduction band and valence band appear at the symmetrical points of the Brillouin zone of K and K'. However, there is a warped structure in the silicene structure, which makes the spin-orbit coupling strength in the silicene structure relatively large, so that the energy gap opened at K and K' is relatively large. Since the warped structure can be changed by applying a vertical electric field, the size of the energy gap can be controlled externally. When a Zeeman field is applied, the energy band structure of silicene occupies a completely spin-polarized state near the two Dirac points in the Brillouin zone. Therefore, the spin of the current passing through the silicene two-terminal device can be completely polarized. In order to achieve the purpose of controlling the polarization direction of the current. When the non-polarized current passes through the three-terminal device, the currents with different spin polarization directions flow out from the other two electrodes respectively, and the spin separation is realized. However, the interface effect between the device and the electrode has a significant impact on the spin polarizability.

One of the research hotspots in condensed matter physics is to explore the properties of quantum systems at the nanometer scale and seek a new generation of quantum electronic devices. With the development of spintronics, the ability to effectively manipulate electron spin degrees of freedom has become the focus of attention in the physics and materials communities. Quantum dots are artificially controllable, and the quantum dot devices manufactured by using them have achieved remarkable development, which is a hot direction in the development of nanoelectronic devices today. The spin properties of electrons in quantum dots play an important role, and the use of electron spin in quantum dot devices for quantum information processing is considered to be one of the most promising directions for realizing future quantum computers. A lot of research on quantum dots was carried out in the 1990s. So far, quantum dots have been a standard technology for trapping single-electron charges. Electrons can be trapped for as long as you want. When an electron tunnels out of a quantum dot, the change in charge can be measured on the order of μs. Controlling individual spins and measuring the spin of individual electrons is very difficult compared to controlling the charge, and fortunately, these techniques have already been developed. The results show that a quantum dot can confine one or two electrons; the spin of a single electron can be adjusted to be placed in a superposition state of up and down; two spins can be adjusted to interact, and then Forming an entangled state, such as a spin singlet or a spin triplet, the consequences of these manipulations can be measured independently of each other's spins. The ability to have complete control over the spins of electrons independent of each other allows us to study the dynamics of single spins in a fully quantum regime in solid-state environments.

Quantum dots are solid artificial submicron structures, typically containing 10 ³ to 10 ⁹ atoms and a considerable number of electrons. In semiconductor quantum dots, all but a few free electrons are tightly bound, and this number varies from zero to several thousand. Firstly, the spin of each electron in a quantum dot is directly affected by the external magnetic field in the form of Zeeman energy, and secondly, the Pauli exclusion principle prohibits two electrons with the same spin direction from occupying the same orbital, So different electrons go into different orbitals, which usually results in different energy states with different energies. Finally, Coulomb interactions lead to energy differences (energy exchange) between different energy states with symmetric and antisymmetric orbital wave functions. Because quantum dots have the characteristics of quantized energy level, adjustable number of beamed electrons, and adjustable energy level, we propose a single-electron spin filter method based on quantum dots.

Contents of the invention

The technical problem to be solved by the utility model is to provide a quantum dot-based single-electron spin filter based on the quantum-dot structure of the single-electron transistor, and adopt an external control method to make the self- After the spin non-polarized electrons pass through the single electron transistor, they become spin polarized electrons, and the spin direction of the electrons can be determined and counted.

The technical scheme adopted by the utility model is: a single electron spin filter based on quantum dots, the main component is a single electron transistor, and the single electron transistor has a Coulomb island, a source, a drain and a gate, and the quantum dot is used as a single electron spin filter. The Coulomb island of the electronic transistor, the Coulomb island is connected to the source and the drain with a tunneling barrier, and the Coulomb island is capacitively coupled to the gate; the single-electron transistor is placed in a vertical magnetic field, and the drain output of the single-electron transistor is connected to the The spintronic readout circuit is placed in a horizontal non-uniform magnetic field.

In the above technical solution, the quantum dots are graphene quantum dots.

In the above technical scheme, the Coulomb island, source, drain and gate of the single-electron transistor are integrated on the silicon dioxide substrate formed on the surface of the silicon substrate, and the Coulomb island, tunneling barrier, source, drain An aluminum oxide protective layer is then deposited on the electrode and the grid.

The single-electron spin filter method based on the quantum dot-based single-electron spin filter above, the quantum dot is used as the Coulomb island of the single-electron transistor, and its discrete energy level undergoes Zeeman splitting in a vertical magnetic field, and the split energy level has spin correlation , with a spin filter effect.

In the above technical scheme, the source and drain bias voltages and gate voltages of the single-electron transistor are adjusted so that the Zeeman splitting energy level of the quantum dot with a specific spin direction of spin up or spin down is located at the source and drain bias voltage. The window forms the single electron transport channel of the single electron transistor to complete the single electron spin filter; the source and drain bias voltage and gate voltage of the single electron transistor can be adjusted so that the Zeeman splitting energy level of the quantum dot is not located at the source and drain The bias window, which closes the electron channel of the single-electron transistor, so that no electrons are spin-polarized;

In the above technical solution, the spin-polarized outgoing electrons through the single-electron transistor will be deflected in the direction of motion under the action of the horizontal non-uniform magnetic field, so as to realize separation and detection; the electrons with opposite spin directions, their magnetic moment The orientation is opposite, when moving in the horizontal non-uniform magnetic field, the motion track is separated due to different force, and reaches two different detectors.

In the above technical solution, the charging energy of the single-electron transistor is greater than the Zeeman splitting energy, and the Zeeman splitting energy is greater than the heat energy.

In the above technical scheme, the size of the source and drain biases is adjusted so that at most one Zeeman splitting energy level can be accommodated in the bias window; by adjusting the source, drain biases and gate voltage, the free electrons on the Coulomb island can be depleted, and then re-injected with a single electron, completing single-electron spin polarization.

In the above technical solution, the source and drain bias voltages remain unchanged, and only the gate voltage is changed, which can adjust a certain energy level with a specific spin direction as an electron channel to move up and down, so as to realize the opening or closing of the electronic channel.

In the above technical solution, the source and drain bias voltages remain unchanged, and only the gate voltage is changed, so that the energy levels of adjacent quantum dots with different spin directions can be adjusted, and appear in the bias voltage window in turn, becoming spin-polarized electron channels.

In the above technical solution, the spin-polarized outgoing electrons through the single-electron transistor are deflected in the direction of motion under the action of the horizontal non-uniform magnetic field, so that they can be separated and detected.

The utility model realizes the spin polarization of a single incident electron and the readout of the spin polarized outgoing electron, which is beneficial to the design of spin electronic devices with fast data processing speed, low power consumption and good stability, and is widely used .

Description of drawings

Figure 1 is a single-electron transistor model of a single quantum dot; in Figure 1, 1 is the source, 2 is the drain, 3 is the gate, 4 is the Coulomb island, and 11 is the tunneling barrier between the source and the Coulomb island , 21 is the tunneling barrier between the drain and the Coulomb island, 31 is the coupling capacitance between the gate and the Coulomb island;

Figure 2 is a schematic diagram of the composition of the spin filter based on quantum dots; in Figure 2, 51 and 52 are the protection resistors of the single-electron transistor, 52 and 53 constitute the voltage divider of the source-drain input voltage, and the single-electron transistor is placed vertically _In the magnetic field B1, the spintronic readout circuit is placed in the horizontal non-uniform magnetic field B2 _;

Figure 3 is a schematic diagram of the principle of a few-electron quantum dot used as a dipolar spin filter; in Figure 3, 12 is the source Fermi level, 22 is the drain Fermi level, 41 and 42 are the Zeeman of the Coulomb island Split level;

Figure 4 is a schematic diagram of the principle of realizing different spin polarizations by adjusting the gate voltage; in Figure 4, (a) is that the free electrons on the quantum dot are depleted, (b) is that a spin-up energy level in the quantum dot is located at the source The drain bias window, (c) is that a spin-down energy level in the quantum dot is located in the source-drain bias window;

Fig. 5 is a schematic diagram of the principle of spin filtering based on quantum dots.

detailed description

Referring to accompanying drawing, the single electron spin filter based on quantum dot of the utility model, main component is single electron transistor, and single electron transistor has Coulomb island, source, drain and gate, and quantum dot is used as single electron transistor Coulomb island, Coulomb island and source and drain are connected by tunneling barrier, and Coulomb island and gate are capacitively coupled; the single electron transistor is placed in a vertical magnetic field, and the drain output terminal of the single electron transistor is connected to the spin electron readout The spintronic readout circuit is placed in a horizontal non-uniform magnetic field, the quantum dots use graphene quantum dots, and the Coulomb island, source, drain and gate of the single-electron transistor are integrated on a silicon substrate On the silicon dioxide substrate formed on the surface, an aluminum oxide protective layer is deposited on the coulomb island, the tunnel barrier, the source electrode, the drain electrode and the gate electrode.

A single-electron spin filtering method using the above-mentioned single-electron spin filter based on quantum dots. Quantum dots are used as Coulomb islands of single-electron transistors, and their discrete energy levels undergo Zeeman splitting in a vertical magnetic field. The split energy levels have self- Spin correlation, with spin filter effect, adjust the source, drain bias voltage and gate voltage of the single electron transistor, so that the quantum dot Zeeman splitting energy level of a specific spin direction with spin up or spin down is located at The source and drain bias voltage windows form the single electron transport channel of the single electron transistor, and complete the single electron spin filter; the source, drain bias voltage and gate voltage of the single electron transistor can be adjusted to make the Zeeman splitting energy level of the quantum dots both Not located in the source and drain bias window, close the electron channel of the single-electron transistor, so that no electrons are spin-polarized, and the spin-polarized outgoing electrons through the single-electron transistor move under the action of a horizontal non-uniform magnetic field The direction will be deflected, so as to achieve separation and detection; electrons with opposite spin directions have opposite magnetic moment orientations. When moving in a horizontal non-uniform magnetic field, the trajectory is separated due to different forces and reaches two different detectors. , the charging energy of the single-electron transistor is greater than the Zeeman splitting energy, and the Zeeman splitting energy is greater than the thermal energy, and the size of the source and drain bias voltages is adjusted so that at most one Zeeman splitting energy level can be accommodated in the bias window; by adjusting the source, The drain bias and gate voltage can deplete the free electrons on the Coulomb island, and then inject a single electron to complete the single electron spin polarization. The source and drain bias remain unchanged, and only the gate voltage is changed, which can be adjusted as an electronic channel. A certain energy level with a specific spin direction moves up and down to realize the opening or closing of the electronic channel. The source and drain bias voltages remain unchanged, and only the gate voltage is changed to adjust the energy levels of adjacent quantum dots with different spin directions. , which in turn appear in the bias window and become the spin-polarized electron channel.

In the above method, the spin-polarized outgoing electrons through the single-electron transistor are deflected under the action of the horizontal non-uniform magnetic field to achieve separation and can be detected.

The quantum dot-based single-electron spin filter of the utility model is based on the Pauli exclusion principle, prohibiting two electrons with the same spin direction of the quantum dot from occupying the same Zeeman splitting energy level, so the electrons enter a specific Orbits in the spin direction are spin-polarized.

The above-mentioned spin-polarized electrons will be separated in the horizontal non-uniform magnetic field and arrive at different detectors due to different orientations of the magnetic moments to complete the detection of the spin state.

To achieve single-electron spin filtering, the following three steps can be used:

(1) Depletion of free electrons on the Coulomb island of the single-electron transistor;

(2) Inject an electron into the Coulomb island of the single-electron transistor;

(3) Measure the spin state of the emitted electrons.

If the Zeeman splitting exceeds the charging energy, electron transport through the quantum dot is spin-polarized, and the quantum dot can be used as a spin filter. As shown in Figure 3, if only the single electron spin-up state energy is in the source-drain bias window, the electron is depleted and contains a free electron during the transport process on the Coulomb island, and the electron is the spin-up pole of.

As shown in Figure 4, in the transport process with one free electron and with two free electrons on the Coulomb island, if no excited state is allowed, because the electron channel already has a spin-up electron, according to Pauli According to the exclusion principle, only one spin-down electron can be allowed to enter the electron channel, so that the outgoing electron is spin-down polarized. Thus, by tuning the quantum dots to correlated transport, the polarization of the spin filter can be electrically reversed.

Below through a specific embodiment of the utility model, in conjunction with accompanying drawing, the method for the single electron spin filter of the utility model is described in further detail:

(1) The single-electron transistor shown in Figure 1 is used as the core component of the single-electron spin filter. The source and drain are respectively coupled to the Coulomb island through tunneling, and the gate is coupled to the Coulomb island through capacitive coupling. As shown in Figure 2, the single-electron transistor completes the spin polarization of a single injected electron, and the spin state of the output electron is detected by a readout circuit.

(2) Adjust the source-drain bias and gate voltage, as shown in Figure 4(a), since the quantum dot spin-up energy level 41 and spin-down energy level 42 are both higher than the electron library Fermi of the source 1 Energy level 12, there are no electrons on the quantum dots.

(3) A positive voltage pulse is applied to the gate, as shown in Figure 4(b), the quantum dot spin-up energy level 41 is adjusted to the source-drain bias window, while the spin-down energy level 42 is still higher than Source 1 electron pool Fermi level 12. Thus, from an energy point of view, an electron is allowed to tunnel above the energy level 41 of the quantum dot, and this electron is spin-up polarized.

(4) If a large positive voltage pulse is applied to the gate, as shown in Figure 4(c), the quantum dot spin-down energy level 42 is adjusted to the source-drain bias window, while the spin-up energy level 41 Electron pool Fermi level 22 below drain 2 . Thus, from an energy point of view, allowing an electron to tunnel above the energy level 42 of the quantum dot, the electron is spin-down polarized.

(5) The electrons incident on the quantum dots will tunnel to the drain 2 after a period of time, as shown in Figure 5. Under the action of the magnetic field, the electrons will receive different forces due to different spin directions, and have different The motion trajectory is detected by the detector.

Quantum dots are a general-purpose system and exist in many different materials and morphologies. The above-mentioned embodiments are only to illustrate the technical conception and characteristics of the present utility model, and its purpose is to enable those familiar with the technology to understand the content of the present utility model and implement it accordingly, and not to limit the protection scope of the present utility model. All other corresponding changes and deformations made according to the technical scheme and technical concept of the utility model shall be covered within the protection scope of the utility model.

Claims (3)

1. a kind of single electron spin filter based on quantum dot, it is characterised in that：Chief component is single-electronic transistor, Single-electronic transistor has coulomb island, source electrode, a drain and gate, quantum dot as single-electronic transistor coulomb island, coulomb island It is connected with tunneling barrier with source electrode and drain electrode, coulomb island is coupled with grid with capacitive form；Single-electronic transistor is placed in perpendicular magnetic In, the drain output connection spinning electron reading circuit of single-electronic transistor, it is non-that spinning electron reading circuit is placed in level In uniform magnetic field.

2. the single electron spin filter based on quantum dot according to claim 1, it is characterised in that：The quantum dot is adopted Use graphene quantum dot.

3. the single electron spin filter based on quantum dot according to claim 1, it is characterised in that：The single electron is brilliant The coulomb island of body pipe, source electrode, drain and gate are integrally disposed in the silicon dioxide substrates of silicon substrate surface formation, coulomb island, Deposition has protective layer of alumina on tunneling barrier, source electrode, drain and gate.