Abstract
Properties of spin Seebeck effect (SSE) in a quantum dot (QD) connected to a topological superconductor or semiconductor nanowire with strong spin-orbit interaction are theoretically studied by the noneqilibrium Green’s function method combined with Dyson equation technique. At low temperatures, Majorana zero modes (MZMs) are prepared at the ends of topological superconductor or semiconductor nanowire, and are hybridized to the QD with spin-dependent strength. We consider that the QD is coupled to two leads in the presence of spin heat accumulation (SHA), i.e., spin-dependent temperature in the leads. We find that the thermopower is spin-polarized when the hybridization strength between the QD and one mode of the MZMs depends on electron spin direction, and its spin-polarization can be effectively adjusted by changing the magnitude of SHA. By proper variation of the spin-polarization of the QD-MZM hybridization strength, magnitude of the SHA, dot level, or the direct coupling between the MZMs, 100% spin-polarized or pure thermopower can be generated. Our results may find real usage in high efficiency spintronic devices or detection of the MZMs, which are under current extensive study. The present model is within the reach of current nano-technologies and may by used in high efficiency spin caloritronics devices.
Highlights
In the last decades, generating and manipulating spin current in closed circuits or spin bias in open ones by thermal bias have been successfully realized in experiments
We find that the thermopower is spin-polarized when the hybridization strength between the quantum dot (QD) and one mode of the Majorana zero modes (MZMs) depends on electron spin direction, and its spin-polarization can be effectively adjusted by changing the magnitude of spin heat accumulation (SHA)
This indicates that, for λσ 0 the magnitude of Sσ will be obviously suppressed in left-right symmetrical system as the tunneling of electrons will be compensated by the holes at the three zero points [27,28,29,30], which leads to null thermoelectric effect, i.e., zero thermopower
Summary
In the last decades, generating and manipulating spin current in closed circuits or spin bias in open ones by thermal bias have been successfully realized in experiments. Thermoelectric effect [27,28,29,30,31] was proposed to be used for detecting Majorana zero modes (MZMs), a kind of quasi-particles of Majorana fermions having zero energy that can be realized in nano-scale topological superconductors [32, 33] They are of their own antiparticle and charge neutral [32,33,34,35], and have potential applications in fault-tolerant quantum computation and energy-saving spintronic devices [36]. Our numerical results show that 100% spin-polarized and pure spin thermopower can be obtained by varying several system parameters, such as spin-polarization of the QD-MZM hybridization interaction, inter-MZM coupling strength, magnitude of the SHA, and the dot levels
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