Topological defects of N\'eel order and Kondo singlet formation for Kondo-Heisenberg model on a honeycomb lattice

TL;DR

This paper investigates the interplay of topological defects, Kondo singlet formation, and competing orders in a honeycomb lattice Kondo-Heisenberg model, revealing new insights into quantum criticality and phase competition in heavy fermion systems.

Contribution

It introduces a quantum non-linear sigma model approach to analyze skyrmion defects and identifies Kondo singlets as competing orders alongside antiferromagnetism.

Findings

Kondo singlets are identified as competing orders of antiferromagnetism.

Conduction electrons acquire a Berry phase that cancels the local moments' Berry phase.

Competition between Kondo singlet formation and spin-Peierls order is demonstrated.

Abstract

Heavy fermion systems represent a prototypical setting to study magnetic quantum phase transitions. A particular focus has been on the physics of Kondo destruction, which captures quantum criticality beyond the Landau framework of order-parameter fluctuations. In this context, we study the spin one-half Kondo-Heisenberg model on a honeycomb lattice at half filling. The problem is approached from the Kondo destroyed, antiferromagnetically ordered insulating phase. We describe the local moments in terms of a coarse grained quantum non-linear sigma model, and show that the skyrmion defects of the antiferromagnetic order parameter host a number of competing order parameters. In addition to the spin Peierls, charge and current density wave order parameters, we identify for the first time Kondo singlets as the competing orders of the antiferromagnetism. We show that the antiferromagnetism and various competing singlet orders can be related to each other via generalized chiral transformations of the underlying fermions. We also show that the conduction electrons acquire a Berry phase through their coupling to the hedgehog configurations of the N\'eel order, which cancels the Berry phase of the local moments. Our results demonstrate the competition between the Kondo-singlet formation and spin-Peierls order when the antiferromagnetic order is suppressed, thereby shedding new light on the global phase diagram of heavy fermion systems at zero temperature.