Optimal Single Quantum Dot Heat-to-pure-spin-current Converters

TL;DR

This paper investigates how Coulomb interactions influence the optimization of heat-to-pure-spin-current conversion in quantum dots, revealing conditions for maximum pure spin currents beyond particle-hole symmetry.

Contribution

It provides a detailed analysis of thermoelectric pure spin currents in quantum dots with Coulomb interactions, identifying optimal conditions for maximum spin current generation.

Findings

Pure spin currents can be maximized at specific Coulomb interaction values.

Maximum pure spin current occurs at interaction strengths beyond particle-hole symmetry.

Optimal conditions are achievable with typical gated quantum dot setups.

Abstract

We delve into the conditions under which a quantum dot thermoelectric setup may be tuned to realize an optimal heat-to-pure-spin-current converter. It is well known that a heat-to-pure-spin-current converter may be realized using a non-interacting quantum dot with a spin-split energy spectrum under particle hole symmetry conditions. However, with the inclusion of Coulomb interaction $U$, ubiquitous in typical quantum dot systems, the relevant transport physics is expected to be altered. In this work, we provide a detailed picture of thermoelectric pure spin currents at various Coulomb interaction parameters $U$ and describe the conditions necessary for an exact cancellation of charge transport between energy levels $\epsilon$ and their Coulomb-charged partner levels $\epsilon+U$, so as to yield the largest terminal pure spin currents. A non-trivial aspect pointed out here is that at sufficiently large values of $U$ ($\ge U_0$), pure spin currents tend to optimize at points other than where the particle-hole symmetry occurs. It is also ascertained that a global maximum of pure spin current is generated at a typical value of the interaction parameter $U$. These optimum conditions may be easily realized using a typical gated quantum dot thermoelectric transport setup