Method for obtaining pure spinning thermoelectric force by irradiating T-type quantum dots through light field

Abstract

The invention discloses a method for obtaining pure spin thermoelectric force by irradiating T-type quantum dots with a light field, which comprises the following steps of: coupling two semiconductor quantum dots into a T-type double-quantum-dot structure, applying different temperature fields to electrodes on two sides connected with the quantum dots, and if a magnetic field is applied to the quantum dots, judging whether the quantum dots are in a spin state or not. According to the quantum dot structure, the coupling strength between the quantum dots can be related to the spin degree of freedom, so that when electrons in different spin directions flow through the quantum dot structure, different interference effects can be generated, peaks of spin upward thermoelectric force and spin downward thermoelectric force are separated in the quantum dot energy space, and pure spin thermoelectric force is obtained. The self-spinning thermoelectric force of the T-shaped double-quantum-dot structure is further enhanced by further adjusting the light field, and finally large pure self-spinning thermoelectric force is obtained. According to the method, a basis is provided for designing a quick-response, efficient and low-energy-consumption thermoelectric device, the effect of the method is superior to that of traditional charge thermoelectric potential, and the limitation of low thermoelectric efficiency is broken through.

Description

Technical Field

[0001] The invention relates to a thermoelectric conversion method, and in particular to a method for improving the thermoelectric performance of a coupled multi-quantum dot system. Background Art

[0002] At the current stage, more and more attention is paid to the development of efficient energy converters. Thermoelectric power generation can directly convert thermal energy into electricity and is one of the technologies that effectively utilize ambient heat.

[0003] The thermoelectric conversion efficiency of low-dimensional nanomaterials is much higher than that of traditional materials. Among them, low-dimensional quantum systems, especially nano quantum devices, as relatively ideal systems with enhanced thermoelectric properties, have received increasing attention.

[0004] The quantum dot system has a unique structure and a variety of electron transport properties, so nanodevices with different functions can be designed according to its different structures and properties. Among them, in the coupled multi-quantum dot system, electrons can choose different Feynman paths to tunnel and maintain good quantum coherence, which has a good effect on the thermal transport properties of quantum dots. How to improve the thermoelectric performance (energy conversion efficiency) of the coupled multi-quantum dot system is one of the important issues that need to be solved in the current development. Summary of the invention

[0005] Purpose of the invention: In view of the above-mentioned prior art, an effective and stable method for obtaining pure spin thermoelectric potential in a T-type double quantum dot structure through light field irradiation is proposed, so as to improve the thermoelectric performance of the coupled multi-quantum dot system.

[0006] Technical solution: A method for obtaining pure spin thermoelectric potential by irradiating T-type quantum dots with a light field, comprising:

[0007] Step 1: Couple two semiconductor quantum dots into a T-type double quantum dot structure through a tunnel junction;

[0008] Step 2: spatially restricting the T-type double quantum dot junction structure in three directions: X, Y, and Z;

[0009] Step 3: installing a left electrode and a right electrode on both sides of the T-type double quantum dot structure, and then applying thermal radiation to create a temperature gradient between the left electrode and the right electrode;

[0010] Step 4: injecting electrons into the T-type double quantum dot structure, so that the electrons are separated under the influence of the spin-related coupling of the T-type double quantum dot structure and the temperature gradient;

[0011] Step 5: applying an adjustable light field to the T-type double quantum dot structure, further enhancing the spin thermoelectric potential of the T-type double quantum dot structure by adjusting the light field parameters, and finally obtaining a pure spin thermoelectric potential.

[0012] Furthermore, in step 3, the range of the thermal potential difference generated by the temperature gradient between the left electrode and the right electrode is 5K to 30K.

[0013] Furthermore, in step 1, the particle size range of the semiconductor quantum dots is 2 nm to 1 um.

[0014] Furthermore, in step 3, an electric heating tube is used to apply the heat radiation to the left and right electrode regions.

[0015] Furthermore, in step 5, pure spin thermoelectric potential is finally obtained by adjusting the frequency of the light field.

[0016] Furthermore, by modeling and calculating the T-type double quantum dot structure, the relationship between the charge and spin thermoelectric potential and the quantum dot energy level and Fermi energy under different conditions is obtained, thereby finding the ideal conditions for enhancing the spin thermoelectric potential.

[0017] Furthermore, in step 5, when the frequency of the light field is adjusted, the value change of the thermoelectric potential is sensed by the thermoelectric effect detector, thereby finally obtaining the pure spin thermoelectric potential.

[0018] Beneficial effects: The method of the present invention couples two semiconductor quantum dots into a T-type double quantum dot structure, applies a temperature field to the electrodes on both sides connected to the quantum dots, and applies a magnetic field to the quantum dots. Then, the coupling strength between the quantum dots becomes related to the spin degree of freedom, so that when electrons with different spin directions flow through the quantum dot structure, different interference effects occur, so that the peaks of the spin-up and spin-down thermoelectric potentials are separated in the quantum dot energy space, thereby obtaining a pure thermoelectric potential. The spin thermoelectric potential of the T-type double quantum dot structure is further enhanced by further adjusting the light field, and finally a pure spin thermoelectric potential is obtained.

[0019] The method of the present invention provides a basis for designing fast-response, high-efficiency and low-energy-consumption thermoelectric devices, and its effect is better than traditional charge thermoelectric potential, breaking through the limitation of low thermoelectric efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the model structure of the present invention;

[0021] Figure 2 The conductivity G and the spin thermoelectric potential are used as the energy ε of the 0th quantum dot at different light field frequencies. 0 Function relationship diagram of ;

[0022] Figure 3 It is the charge thermoelectric potential S under the influence of different light field frequencies. c and the spin thermoelectric potential S s Plotted as a function of the Fermi energy μ. DETAILED DESCRIPTION

[0023] The present invention will be further explained below in conjunction with the accompanying drawings.

[0024] like Figure 1 As shown, a method for enhancing the spin thermoelectric potential in a T-type double quantum dot structure by light field irradiation, the specific steps are as follows:

[0025] Step 1: Couple two semiconductor quantum dots QD0 and QD1 into a T-type double quantum dot structure through a tunnel junction.

[0026] Step 2: Apply an electrostatic field through the cathode probe to spatially confine the double quantum dot structure in the X, Y, and Z directions.

[0027] Step 3: A left electrode and a right electrode connected to an external circuit are installed on both sides of the T-shaped double quantum dot structure, and then an electric heating tube is used to apply thermal radiation to the left and right electrode regions, so that there is a temperature gradient between the left and right electrodes. In this embodiment, the thermal potential difference is controlled within the range of 5 to 30 Kelvin (K), so that the spin thermoelectric potential enhancement effect can be achieved to the best extent while reducing the power consumption of the electric heating tube. Figure 1 In the table, L stands for left side, R stands for right side; T L Indicates the temperature on the left, T R Indicates the temperature on the right; V L / R represents the probability amplitude of electrons tunneling from QD0 to the left / right electrode, V * L / R Represents the probability amplitude of electrons tunneling from the left / right electrode to QD0.

[0028] Step 4: To facilitate subsequent experimental research, in this embodiment, an electron flow is injected into the T-type double quantum dot structure through a field emission scanning electron microscope (model: Hitachi SU8200), so that the spin-up and spin-down electrons are separated under the influence of the spin-related coupling of the double quantum dot structure and the thermal potential difference, and move toward the left electrode and the right electrode respectively.

[0029] In other embodiments, the generation and injection of the electron flow may adopt a photoelectric emitter with mature technology.

[0030] Step 5: Apply an adjustable light field U to the T-type double quantum dot structure, and further enhance the spin thermoelectric potential of the T-type double quantum dot structure by adjusting the frequency of the light field, so as to finally obtain pure spin thermoelectric potential.

[0031] In the above process, the semiconductor quantum dot particle size range is selected to be 2nm to 1μm, which allows the T-type double quantum dot structure to more accurately filter mobile electrons with different spin directions.

[0032] The model calculation process of the above method is as follows:

[0033] 1. According to the composition and configuration of the quantum dot structure, assuming that there is no interaction, the Hamiltonian H of the quantum dot system is expressed as:

[0034] H=H Leads +H Dots +H Hop

[0035] Among them, H Leads is the Hamiltonian for an isolated wire in the noninteracting case, where the wire is a model for an electrode:

[0036]

[0037] H Dots is the Hamiltonian of an isolated quantum dot in the non-interacting case:

[0038]

[0039] H Hop is the jumping Hamiltonian between the point and the wire:

[0040]

[0041] In the above three formulas, and c kασ They represent the creation and annihilation operators of an electron with momentum k and spin σ in the wire α(L / R). kασ is the energy of the electrons in the wire. and d iσ They represent the creation and annihilation operators of electrons in quantum dot i, respectively, where the index i takes values ​​of 0 and 1. Since the energy level in quantum dot 1 is affected by the light field, the energy level expression is: ε 1σ (t) = ε 1σ +eVcosωt,ε 1σ =ε 1 +σε z , the energy level ε of the 0th quantum dot 0σ =ε 0 +σε z , ε z = gμ B B, e is the electron charge, V is the amplitude of the light field, ω is the frequency of the light field, ε i is the energy of the ith quantum dot, ε z is the Zeeman energy, g is the Lande factor, μ B is the Bohr magneton, and B is the magnetic induction intensity. 01 and V α It is the tunneling coupling between quantum dots 0 and 1 and between the wire and quantum dot 0. The abbreviation HC stands for Hermitian conjugation.

[0042] 2. Delayed Green's function G of Fermi operators A and B in the time domain r (τ, 0) is defined as:

[0043]

[0044] The equation of motion in the energy domain is:

[0045]

[0046] Here, θ represents the step function and ε is the energy.

[0047] 3. Use the above equation of motion method to calculate the Green's function of quantum dot 1:

[0048]

[0049] Among them, J n is the nth-order Bessel function, n is the order, Γ R is the coupling strength between the left wire and quantum dot 0.

[0050] 4. System transmission probability T σ for:

[0051] T σ = -ΓIm[《d 0σ , d 0σ 》]

[0052] Where Γ = Γ L +Γ R is the total coupling strength and Im is the imaginary part.

[0053] 5. Considering a linear response system, when there is a potential difference ΔV and a temperature difference ΔT at both ends, the charge flow I charge and heat flow I heat It can be expressed as:

[0054]

[0055]

[0056] Where T is the absolute temperature and the kinetic coefficient L is n，σ (μ) is:

[0057]

[0058] Where μ is the chemical potential, h is Planck's constant, and T σ (ε) is the transmission probability of the system.

[0059] The spin-dependent conductance is obtained from the above formula: G σ (μ)=e2L 0，σ(μ).

[0060] 6. The Seebeck coefficient S is proportional to the temperature difference ΔT and the potential difference ΔV when the charge flow disappears, and is defined as:

[0061]

[0062] Charge Seebeck coefficient S c (μ) and the spin Seebeck coefficient S s (μ) is expressed as:

[0063] S cs (μ)≡S ↑ (μ)+(-)S ↓ (μ)

[0064] Among them, S ↑ (μ) represents the spin-up Seebeck coefficient, S ↓ (μ) represents the spin-down Seebeck coefficient.

[0065] 7. Use Mathematica computing software to program and solve the above equations. Through numerical calculation, the relationship between charge and spin thermoelectric potential and quantum dot energy level and Fermi energy under different conditions is obtained, and the ideal conditions for enhancing spin thermoelectric potential are found. In practical applications, the value and change of thermoelectric potential can be sensed by thermoelectric effect detectors.

[0066] Reference Figure 2 (a) shows the relationship between the conductivity G as a function of the energy of the 0th quantum dot in the absence of electric field (ω = 0) and different light field frequencies (ω = 0.3, 0.6, 0.9, 1.2), and the coupling coefficient between the two quantum dots is set to t 01 = 0.8, Γ = 1 meV, fixed light field amplitude V = 1. It can be seen that as the frequency of the light field increases, ε in the conductance diagram 0 = 0, the main resonance peak changes from a valley value to a peak value, and then to a valley value again, that is, the conductivity increases first and then decreases. This is a very sensitive system, so the energy level of the quantum dot and the frequency of the light field can be adjusted to obtain the appropriate conductivity. Figure 2 In (b), ε z =0.015,ε 1 =μ=0, V=1, and it is found that the Seebeck coefficient can be adjusted by adjusting the frequency of the light field: the higher the frequency of the light field, the larger the Seebeck coefficient.

[0067] Reference Figure 3 By changing the frequency of the light field, a larger thermochemical potential can be obtained at the appropriate Fermi level. Figure 3In (a), the fluctuation peak of the charge Seebeck coefficient is large. As the frequency increases, the sign of the charge thermochemical potential changes suddenly. By adjusting the frequency of the light field, a larger charge thermochemical potential can be obtained at certain Fermi energies. Figure 3 In (b), there are multiple sign mutations of the spin thermochemical potential as the frequency of the light field changes. What is significant is that at μ = 0, where the charge thermochemical potential is zero, the spin thermochemical potential is not zero, and a pure spin thermochemical potential appears, which can be enhanced by appropriately increasing the frequency of the light field (μ = 0). In summary, a T-type double quantum dot system with strong charge and spin thermochemical potential can be obtained by adjusting the frequency of the light field, so the method of the present invention is conducive to improving the efficiency of thermoelectric conversion.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for obtaining pure spin thermoelectric potential by irradiating T-type quantum dots with a light field, characterized in that: include: Step 1: Couple two semiconductor quantum dots into a T-type double quantum dot structure through a tunnel junction; Step 2: spatially restricting the T-type double quantum dot junction structure in three directions: X, Y, and Z; Step 3: installing a left electrode and a right electrode on both sides of the T-type double quantum dot structure, and then applying thermal radiation to create a temperature gradient between the left electrode and the right electrode; Step 4: injecting electrons into the T-type double quantum dot structure, so that the electrons are separated under the influence of the spin-related coupling of the T-type double quantum dot structure and the temperature gradient; Step 5: applying an adjustable light field to the T-type double quantum dot structure, further enhancing the spin thermoelectric potential of the T-type double quantum dot structure by adjusting the light field parameters, and finally obtaining a pure spin thermoelectric potential.

2. The method for obtaining pure spin thermoelectric potential by light field irradiation of T-type quantum dots according to claim 1, characterized in that: In step 3, the range of the thermal potential difference generated by the temperature gradient between the left electrode and the right electrode is 5K to 30K.

3. The method for obtaining pure spin thermoelectric potential by light field irradiation of T-type quantum dots according to claim 1, characterized in that: In the step 1, the particle size range of the semiconductor quantum dots is 2nm to 1um.

4. The method for obtaining pure spin thermoelectric potential by light field irradiation of T-type quantum dots according to claim 1 or 2, characterized in that: In the step 3, an electric heating tube is used to apply the heat radiation to the left and right electrode regions.

5. The method for obtaining pure spin thermoelectric potential by irradiating T-type quantum dots with a light field according to any one of claims 1 to 3, characterized in that: In the step 5, the pure spin thermoelectric potential is finally obtained by adjusting the frequency of the light field.

6. The method for obtaining pure spin thermoelectric potential by light field irradiation of T-type quantum dots according to claim 5, characterized in that: By modeling and calculating the T-type double quantum dot structure, the relationship between the charge and spin thermoelectric potential and the quantum dot energy level and Fermi energy under different conditions is obtained, thereby finding the ideal conditions for enhancing the spin thermoelectric potential.

7. The method for obtaining pure spin thermoelectric potential by light field irradiation of T-type quantum dots according to claim 5, characterized in that: In the step 5, when the frequency of the light field is adjusted, the value change of the thermoelectric potential is sensed by the thermoelectric effect detector, so that the pure spin thermoelectric potential is finally obtained.

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