Transport through a Kondo quantum dot: Functional RG approach

TL;DR

This paper employs the functional renormalization group method to compute the conductance of a Kondo quantum dot, analyzing behavior across different temperature and voltage regimes and discussing challenges near strong coupling.

Contribution

It introduces a FRG-based approach to calculate quantum dot conductance in the Kondo regime starting from the Keldysh formalism, including analysis of strong coupling difficulties.

Findings

Conductance calculations match known high-temperature and high-voltage limits.

Identifies challenges in approaching the strong coupling regime.

Proposes potential improvements for strong coupling analysis.

Abstract

We apply the functional renormalization group (FRG) method to calculate the conductance of a quantum dot in the Kondo regime. Starting from the exact FRG equations in Keldysh formulation for the Kondo exchange Hamiltonian in pseudo-fermion (pf) representation, we solve the coupled equations for the pf self energy and the coupling function, neglecting three-particle and higher correlation functions. The conductance $G$ as a function of temperature $T$ and bias voltage $V$ is calculated using a renormalized Golden Rule expression. The limiting behavior at $T$ and/or $V$ $\gg T_{K}$ ($T_{K}$ : Kondo temperature) agrees with known results. The difficulties when approaching strong coupling are analyzed and improvements are suggested.