Parity-time symmetry breaking in spin chains

TL;DR

This paper explores how parity-time symmetry breaking occurs in classical Heisenberg spin chains under spin-transfer torque, revealing a phase transition characterized by the zeros of the partition function, linking equilibrium concepts to nonequilibrium systems.

Contribution

It introduces a novel analysis of PT symmetry-breaking in spin chains driven by non-conservative forces using Lee-Yang zeros, bridging equilibrium and nonequilibrium physics.

Findings

Identifies a PT symmetry-breaking phase transition driven by spin-transfer torque.

Shows the connection between Lee-Yang zeros and nonequilibrium phase transitions.

Proposes experimental observation of Lee-Yang zeros in physical systems with imaginary magnetic fields.

Abstract

We investigate nonequilibrium phase transitions in classical Heisenberg spin chains associated with spontaneous breaking of parity-time ($\mathcal{PT}$) symmetry of the system under the action of Slonczewski spin-transfer torque (STT) modeled by an applied \textit{imaginary} magnetic field. We reveal the STT-driven $\mathcal{PT}$ symmetry-breaking phase transition between the regimes of precessional and exponentially damped spin dynamics and show that its several properties can be derived from the distribution of zeros of the system's partition function, the approach first introduced by Yang and Lee for studying equilibrium phase transitions in Ising spin chains. The physical interpretation of imaginary magnetic field as describing the action of non-conservative forces opens the possibility of direct observations of Lee-Yang zeros in nonequilibrium physical systems.