Impurities near an Antiferromagnetic-Singlet Quantum Critical Point

TL;DR

This paper uses quantum Monte Carlo simulations to study how impurities affect antiferromagnetic and singlet states near a quantum critical point, linking local NMR signals to critical behavior.

Contribution

It introduces a unified framework connecting impurity-induced AF domains and NMR relaxation rates near an AF-singlet quantum critical point.

Findings

Impurities induce AF domains on the singlet side of the transition.

NMR relaxation rate $1/T_1$ correlates with impurity susceptibility and AF order parameter.

Results agree with experiments on Cd-doped CeCoIn$_5$.

Abstract

Heavy fermion systems, and other strongly correlated electron materials, often exhibit a competition between antiferromagnetic (AF) and singlet ground states. Using exact Quantum Monte Carlo (QMC) simulations, we examine the effect of impurities in the vicinity of such AF- singlet quantum critical points, through an appropriately defined impurity susceptibility, $\chi_{imp}$. Our key finding is a connection, within a single calculational framework, between AF domains induced on the singlet side of the transition, and the behavior of the nuclear magnetic resonance (NMR) relaxation rate $1/T_1$. We show that local NMR measurements provide a diagnostic for the location of the QCP which agrees remarkably well with the vanishing of the AF order parameter and large values of $\chi_{imp}$. We connect our results with experiments on Cd-doped CeCoIn$_5$.