Continuous-Time Quantum Monte Carlo Approach to Singlet-Triplet Kondo Systems

TL;DR

This paper employs a continuous-time quantum Monte Carlo method to analyze the dynamical properties of a Kondo model with competing singlet and triplet crystal electric field levels, revealing unique spectral features.

Contribution

It introduces a sign-problem-free quantum Monte Carlo approach to study the dynamical responses in singlet-triplet Kondo systems, highlighting novel spectral behavior.

Findings

Dynamical response exhibits a quasi-elastic peak when CEF splitting is near the Kondo temperature.

The local single-particle spectrum shows an energy gap, contrasting with the ordinary Kondo model.

The method effectively avoids the negative sign problem in simulations.

Abstract

Dynamical properties are studied numerically for a variant of the Kondo model with singlet and triplet crystalline electric field (CEF) levels where Kondo and CEF singlets compete for the ground state. Using the continuous-time quantum Monte Carlo method, we derive the $t$-matrix of conduction electrons and dynamical susceptibilities of local electrons without encountering the negative sign problem. When the CEF splitting is comparable to the Kondo temperature, the dynamical response has only a quasi-elastic peak. Nevertheless, the local single-particle spectrum shows an energy gap in strong contrast with the ordinary Kondo model.