# Raman scattering from current-stabilized nonequilibrium phases in Ca$_2$RuO$_4$

## TL;DR

This study uses Raman scattering to show that electrical current can induce a semimetallic phase in Ca$_2$RuO$_4$ without significant heating, revealing a genuine nonequilibrium phase with unique properties.

## Contribution

It demonstrates that current-induced phases in Ca$_2$RuO$_4$ are distinct from equilibrium states and are not caused by Joule heating, using Raman spectroscopy and temperature analysis.

## Key findings

- Current induces a semimetallic state without significant heating.
- No long-range antiferromagnetic order in the current-induced phase.
- Phonon Fano broadening indicates coupling to charge and orbital fluctuations.

## Abstract

We used Raman light scattering to study the current-stabilized nonequilibrium semimetallic and metallic phases in Ca$_2$RuO$_4$. By determining the local temperature through careful analysis of the Stokes and anti-Stokes intensities, we find that Joule heating can be completely avoided by supplying sufficient cooling power in a helium-flow cryostat, and that the current induces the semimetallic state without inducing any significant heating. We further investigate the current-induced semimetallic state as a function of temperature and current. We confirm the absence of long-range antiferromagnetic order and identify a substantial Fano broadening of several phonons, which suggests coupling to charge and orbital fluctuations. Our results demonstrate that the semimetallic state is a genuine effect of the applied electrical current and that the current-induced phases have characteristics distinct from the equilibrium ones.