Excess conductance of a spin-filtering quantum dot

TL;DR

This paper develops a quantum mechanical theory for excess conductance in a spin-filtering quantum dot, exploring how it can be used to measure spin relaxation time T_1 independently of other parameters.

Contribution

It provides a theoretical framework to determine T_1 from conductance measurements in a chaotic quantum dot under magnetic fields, independent of dephasing time and charging energy.

Findings

Excess conductance increases from 1/2 to 2/3 e^2/h with spin-flip scattering.

In a magnetic field, average conductance follows a specific formula involving T_1, Delta, and h.

The theory allows T_1 measurement independently of tau_phi and C.

Abstract

The conductance G of a pair of single-channel point contacts in series, one of which is a spin filter, increases from 1/2 to 2/3 x e^2/h with more and more spin-flip scattering. This excess conductance was observed in a quantum dot by Zumbuhl et al., and proposed as a measure for the spin relaxation time T_1. Here we present a quantum mechanical theory for the effect in a chaotic quantum dot (mean level spacing Delta, dephasing time tau_phi, charging energy e^2/C), in order to answer the question whether T_1 can be determined independently of tau_phi and C. We find that this is possible in a time-reversal-symmetry-breaking magnetic field, when the average conductance follows closely the formula <G>=(2e^2/h)(T_1+h/Delta)/(4T_1+3h/Delta).