Anti-Resonance and the 0.7 Anomaly in Conductance through a Quantum Point Contact

TL;DR

This paper models electron transmission through a quantum point contact, explaining the 0.7 conductance anomaly via anti-resonance effects caused by a local bound state and its modulation by Kondo screening.

Contribution

It introduces a quasi-one-dimensional model with a local bound state to explain the 0.7 anomaly and the role of anti-resonance and Kondo effects in conductance.

Findings

Anti-resonance causes a 0.75 conductance shoulder.

Kondo screening reduces anti-resonance effects at low temperatures.

Model explains conductance plateaus and anomalies in quantum point contacts.

Abstract

We investigate the transmission of electrons through a quantum point contact by using a quasi-one-dimensional model with a local bound state below the band bottom. While the complete transmission in lower channels gives rise to plateaus of conductance at multiples of $2e^{2}/h$, the electrons in the lowest channel are scattered by the local bound state when it is singly occupied. This scattering produces a wide zero-transmittance (anti-resonance) for a singlet formed by tunneling and local electrons, and has no effect on triplets, leading to an exact $0.75(2e^{2}/h)$ shoulder prior to the first $2e^{2}/h$ plateau. Formation of a Kondo singlet from electrons in the Fermi sea screens the local moment and reduces the effects of anti-resonance, complementing the shoulder from 0.75 to 1 at low temperatures.