Thermoelectric And Thermo-Spin Effects In Semiconductor Quantum Dots

In recent years, with the constantly rapid development of nanotechnology,nano-structure of local thermal effects had been studied widely. Since the spin-Seebeckeffect has been observed in2008, it attracted numerous researchers’ interest in structure ofsemiconductor quantum dots. As the quantum dot became one of the candidates for thefuture quantum calculation and quantum information implementation, study the heattransport and transformation, have practical significance for understanding spin transport,reducing energy consumption, and optimize the design of electronic devices. In this paper,we study the thermoelectric and thermo-spin effect in a quantum dots system under themodulation of local declination magnetic field, hoping to find the enhancement ofconversion efficiency in a suitable range in theory. Otherwise, it should be noted that thespin coherence is interfered with environment. Thus, information storage and readout inquantum dot under thermal bias became another starting point of this study.In the research of thermoelectric and thermal spin, we use the non-equilibriumGreen’s function method to improve the quantum tunneling rate equations and toinvestigate a quantum dot coupled with the ferromagnetic leads system. It concluded thatthe local declination magnetic field induced electronic level Zeeman splitting on theprojection direction of spin angular momentum. By setting the angle of local magneticdeclination, thermoelectric conversion quality factor can be controlled in a quantum dotsystem. Meanwhile, the local magnetic field in the vertical direction induced electron spinprecession, which could make electronic spin states coherent superposition in the quantumdot. This process had an effect on electrons tunneling between the quantum dot and theleads. Further study found that thermo-spin figures of merit were saturated with theaugmentation of the magnetic field in the case of parallel polarization leads. It means thatwe hardly reach to purpose only by adjusting the magnetic field. In the case of anti-parallelpolarization leads, we adopted the Zeeman splitting energy to break Coulomb blockaderestrictions and to obtain a high thermo-spin figure of merit under the auxiliary of a vertical magnetic field.In the study of single electron spin bit storage and reading out in the quantum dotunder the thermal bias, the master equation of a quantum dot system had been derived byusing the open system of reduced density matrix method in the general situation. Theresearch showed that it would be unable to store a single electron spin bit in the quantumdot completely, and the unfavorable impact, couldn’t make it eliminated only by adjustingthe intensity of the spin bias. In the process of spin down electrons readout, thermal biascould lead to the decrement of current intensity peak. The larger thermal bias results in themore obvious decay, which is independent of the thermal bias direction. The thermal biasaffected electronic tunneling in the spin up state of the electron readout stage, which couldproduce a non-zero current in the leads. Due to the Pauli Exclusion Principle, the chargecurrent was quietly tiny comparing to spin down electrons readout, thus could get rid ofdisadvantage effect by subjective comparison.