The Signs of Quantum Dot-Lead Matrix Elements: The Effect on Transport vs. Spectral Properties

TL;DR

This paper investigates how the signs of coupling matrix elements between a quantum dot and leads influence transport and spectral properties, revealing robust conductance zeros and phase lapses.

Contribution

It demonstrates the impact of coupling sign variations on conductance and phase behavior, highlighting phenomena like conductance zeros and phase lapses in quantum dots.

Findings

Conductance can vanish at spectral density maxima due to coupling signs.

Zero conductance points are robust against increased dot-lead coupling.

Phase lapses of -π are associated with conductance zeros and vanish as temperature decreases.

Abstract

A small quantum dot coupled to two external leads is considered. Different signs of the dot-leads coupling matrix elements give rise to qualitatively different behavior of physical observables such as the conductance, the phase of the transmission amplitude and the differential capacitance of the dot. For certain relative signs the conductance may vanish at values of the gate potential, where the spectral density is maximal. Zeroes of the conductance are robust against increasing the dot-lead coupling. They are associated with abrupt phase lapses in the transmission phase whose width vanishes as the square of the temperature. We carefully distinguish between phase lapses of $-\pi$ and phase anti-lapses of $\pi$.