Field-tuned quantum critical point of antiferromagnetic metals

TL;DR

This paper theoretically analyzes how a magnetic field influences the quantum critical behavior of three-dimensional antiferromagnetic metals, revealing the role of spin precession and damping in thermodynamic properties near the critical point.

Contribution

It introduces a detailed theoretical framework for understanding field-induced quantum criticality in antiferromagnetic metals, highlighting the impact of spin precession on critical behavior.

Findings

Precession can reverse the sign of the  correction to specific heat.

A maximum in specific heat coefficient c(T)/T can occur due to precession effects.

Susceptibility shows significant changes near the quantum critical point, revealing spin-spin interactions.

Abstract

A magnetic field applied to a three-dimensional antiferromagnetic metal can destroy the long-range order and thereby induce a quantum critical point. Such field-induced quantum critical behavior is the focus of many recent experiments. We investigate theoretically the quantum critical behavior of clean antiferromagnetic metals subject to a static, spatially uniform external magnetic field. The external field does not only suppress (or induce in some systems) antiferromagnetism but also influences the dynamics of the order parameter by inducing spin precession. This leads to an exactly marginal correction to spin-fluctuation theory. We investigate how the interplay of precession and damping determines the specific heat, magnetization, magnetocaloric effect, susceptibility and scattering rates. We point out that the precession can change the sign of the leading \sqrt{T} correction to the specific heat coefficient c(T)/T and can induce a characteristic maximum in c(T)/T for certain parameters. We argue that the susceptibility \chi =\partial M/\partial B is the thermodynamic quantity which shows the most significant change upon approaching the quantum critical point and which gives experimental access to the (dangerously irrelevant) spin-spin interactions.