Field-induced Antiferromagnetism and the Kondo Insulator-to-Metal Transition

TL;DR

This paper investigates how magnetic fields induce antiferromagnetism and cause a transition from an insulating to a metallic state in a Kondo lattice model, combining mean field theory and quantum Monte Carlo simulations.

Contribution

It provides a detailed analysis of the magnetic field effects on Kondo insulators, revealing a separation of energy scales for magnetic ordering and charge gap closure, supported by numerical simulations.

Findings

Spin gap closes at Zeeman energy comparable to Kondo energy.

Charge gap persists until higher hybridization energy.

Quantum Monte Carlo supports the mean field results.

Abstract

The Kondo lattice model, augmented by a Zeeman term, serves as a useful model of a Kondo insulator in an applied magnetic field. A variational mean field analysis of this system on a square lattice, backed up by quantum Monte Carlo calculations, reveals an interesting separation of magnetic field scales. For Zeeman energy comparable to the Kondo energy, the spin gap closes and the system develops transverse staggered magnetic order. The charge gap, however, survives up to a higher hybridization energy scale, at which point the canted antiferromagnetism is suppressed and the system becomes metallic. Quantum Monte Carlo simulations support this mean field scenario. An interesting rearrangement of spectral weight with magnetic field is found.