Quantum Monte Carlo studies of U(1) lattice gauge models of Kondo breakdown

TL;DR

This paper uses quantum Monte Carlo simulations to study U(1) gauge theories of heavy fermions, revealing distinct metallic phases and demonstrating gauge-mediated Kondo breakdown with specific transport signatures.

Contribution

It provides a nonperturbative analysis of Kondo breakdown in U(1) gauge theories, identifying spectral and transport signatures of phase transitions in heavy fermion systems.

Findings

Identification of heavy-fermion metal and Kondo-breakdown metal regimes

Demonstration of gauge-mediated Kondo breakdown

Transport fingerprints of orbital-selective Mott transition

Abstract

In the local-moment regime, heavy fermions are most economically described by a compact U(1) gauge theory. With this formulation of the Kondo lattice, we study a spin chain coupled to two-dimensional Dirac conduction electrons. The spin chain is described by fermionic partons carrying spin and U(1) gauge charge. The heavy-fermion quasiparticle is a bound state of a U(1) matter field carrying unit electric and U(1) gauge charge, and the fermionic parton. Using sign-problem-free determinant quantum Monte Carlo simulations, we identify two symmetry-equivalent regimes: a heavy-fermion metal with a sharp composite-fermion resonance and robust low-frequency transport, and a Kondo-breakdown metal with an incoherent resonance and vanishing low-frequency transport. For any finite lattice extent in the direction perpendicular to the chain, the Luttinger volume of the heavy-fermion phase counts both composite and conduction electrons, while in the Kondo-breakdown phase it counts only the conduction electrons. The evolution of the composite-fermion spectrum, dynamical spin structure factor, and optical conductivity provides a nonperturbative demonstration of gauge-mediated Kondo breakdown and establishes transport fingerprints of an orbital-selective Mott transition in the context of U(1) gauge theories of heavy fermions.