Enhanced Thermoelectricity in Nanowires with inhomogeneous Helical states

TL;DR

This paper demonstrates that inhomogeneous Rashba spin-orbit coupling in semiconductor nanowires can significantly enhance thermoelectric performance by tuning spin orientations, leading to violations of classical laws and improved efficiency.

Contribution

It introduces a method to control thermoelectric properties in nanowires via spin-orbit misalignment, revealing new ways to optimize thermoelectric devices using spin control.

Findings

Antiparallel RSOC vectors cause violation of Wiedemann-Franz law.

Significant enhancement of Seebeck coefficient and ZT.

Optimal doping and temperature windows depend on Zeeman gap.

Abstract

Semiconductor nanowires (NWs) with strong Rashba spin-orbit coupling (RSOC), when exposed to a suitably applied Zeeman field, exhibit one-dimensional helical channels with a spin orientation locked to the propagation direction within the magnetic energy gap. Here, by adopting a scattering-matrix approach applied to a tight-binding model of the NW, we demonstrate that the thermoelectric (TE) properties can be widely controlled by tuning the misalignment angle $\phi$ between the spin-orbit directions of two NW segments. In particular, when the RSOC vectors are antiparallel (Dirac paradox configuration) we predict a significant violation of the Wiedemann-Franz law, and a strong enhancement of the Seebeck coefficient and the $ZT$ figure of merit. We also show that the Zeeman gap determines the optimal energy window for doping and temperatures. These results suggest that controlling the spin-orbit field direction, which can be achieved with suitably applied wrap gates, is a promising alternative for tuning and optimizing the TE response in quantum-coherent semiconducting NW devices.