Dynamical phase transition in a strongly hybridized phonon-triplon chain

TL;DR

This paper investigates how strong phonon-triplon coupling in a driven spin chain leads to non-equilibrium phase transitions, revealing sharp spectral changes and mapping the phase diagram for potential experimental observation.

Contribution

It demonstrates the occurrence of first-order phase transitions due to strong hybridization in a driven spin-phonon system using mean-field Lindblad and Floquet analyses.

Findings

Sharp first-order phase transitions in emission spectra

Analytical confirmation via Floquet analysis

Complete steady-state phase diagram mapped

Abstract

We study a dimerized spin-1/2 chain, such as CuGeO$_3$, hosting triplon excitations coupled to optical phonons under weak terahertz laser driving. Both phonons and triplons weakly lose energy into the surrounding baths, forming a non-equilibrium steady state. In the strong phonon-triplon coupling regime, phonons near the two-triplon continuum hybridize strongly with triplons. Using mean-field Lindblad dynamics, we show that this strong hybridization induces sharp first-order phase transitions -- either single or simultaneous double -- in the emission spectrum, mainly due to dissipation-induced nonlinearities. Using mean-field Floquet analysis of harmonic modes in both sectors, we analytically confirm the existence of these phase transitions. Furthermore, we map the complete steady-state phase diagram by varying key control parameters and provide experimentally relevant parameters for observing these transitions in laser-driven CuGeO$_3$.