Transmission phase lapses in quantum dots: the role of dot-lead coupling asymmetry

TL;DR

This paper explains the systematic transmission phase lapses in quantum dots as a consequence of asymmetric dot-lead couplings and interaction-induced level population switching, providing a mean field analysis of the phenomenon.

Contribution

It demonstrates that phase lapses can be explained by asymmetries and interactions in a two-level quantum dot, offering a mean field theoretical framework.

Findings

Phase lapses are linked to asymmetric couplings and population switching.

Mean field analysis reveals continuous and discontinuous behaviors in the quantum dot's response.

The phenomenon is shown to be generic across similar quantum dot systems.

Abstract

Lapses of transmission phase in transport through quantum dots are ubiquitous already in the absence of interaction, in which case their precise location is determined by the signs and magnitudes of the tunnelling matrix elements. However, actual measurements for a quantum dot embedded in an Aharonov-Bohm interferometer show systematic sequences of phase lapses separated by Coulomb peaks -- an issue that attracted much attention and generated controversy. Using a two-level quantum dot as an example we show that this phenomenon can be accounted for by the combined effect of asymmetric dot-lead couplings (left lead/right lead asymmetry as well as different level broadening for different levels) and interaction-induced "population switching" of the levels, rendering this behaviour generic. We construct and analyse a mean field scheme for an interacting quantum dot, and investigate the properties of the mean field solution, paying special attention to the character of its dependence (continuous vs. discontinuous) on the chemical potential or gate voltage.