Singular conductance of a spin 1 quantum dot

TL;DR

This paper explains the zero-bias anomaly observed in spin-1 quantum dots through an underscreened Kondo effect, revealing singular conductance behavior due to broad Kondo temperature distributions.

Contribution

It provides a detailed many-body calculation confirming the singular temperature and voltage dependence of conductance in spin-1 quantum dots.

Findings

Conductance exhibits 1/T and 1/V singularities.

Underscreened Kondo physics dominates over a broad temperature range.

Theoretical predictions match experimental observations.

Abstract

We interpret the recent observation of a zero-bias anomaly in spin-1 quantum dots in terms of an underscreened Kondo effect. Although a spin-1 quantum dots are expected to undergo a two-stage quenching effect, in practice the log normal distribution of Kondo temperatures leads to a broad temperature region dominated by underscreened Kondo physics. General arguments, based on the asymptotic decoupling between the partially screened moment and the leads, predict a singular temperature and voltage dependence of the conductance $G$ and differential conductance $g$, resulting in $dg/dT\sim 1/T$ and $dG/dV \sim 1/V$. Using a Schwinger boson approach, we show how these qualitative expectations are borne out in a detailed many body calculation.