Spin filtering and thermopower in star coupled quantum dot devices

TL;DR

This paper investigates thermoelectric and spin transport in star-configured triple quantum dot devices, revealing how magnetic fields and quantum effects influence thermopower and spin polarization.

Contribution

It introduces a detailed analysis of spin filtering and thermopower in star quantum dot systems, highlighting the impact of Kondo effects and magnetic fields on transport properties.

Findings

Large spin thermopower peaks (~k_B/|e|) under magnetic fields.

High spin polarization (~100%) due to interference effects.

Behavior similar in systems with multiple side-coupled quantum dots.

Abstract

We analyze the linear thermoelectric transport properties of devices with three quantum dots in a star configuration. A central quantum dot is tunnel-coupled to source and drain electrodes and to two additional quantum dots. For a wide range of parameters, in the absence of an external magnetic field, the system is a singular Fermi liquid with a non-analytic behavior of the electric transport properties at low energies. The singular behavior is associated with the development of a ferromagnetic or an underscreened Kondo effect, depending on the parameter regime. A magnetic field drives the system into a regular Fermi liquid regime and leads to a large peak ($\sim k_B/|e|$) in the spin thermopower as a function of the temperature, and to a $\sim 100\%$ spin polarized current for a wide range of parameters due to interference effects. We find a qualitatively equivalent behavior for systems with a larger number of side coupled quantum dots, with the maximum value of the spin thermopower decreasing as the number of side-coupled quantum dots increases.