Nonequilibrium Orbital Transitions via Applied Electrical Current in Calcium Ruthenate

TL;DR

This study demonstrates how applied electrical current can induce nonequilibrium orbital transitions and modify structural and magnetic properties in calcium ruthenate, revealing a new way to control complex oxide phases.

Contribution

It introduces a novel approach to manipulate orbital and magnetic orders via electrical current in Ca2RuO4, supported by experimental phase diagrams and theoretical interpretation.

Findings

Electrical current reduces orthorhombicity and octahedral rotations.

A critical current density separates magnetic and orbital phases.

High current densities induce glassy, metastable behaviors.

Abstract

Simultaneous control of structural and physical properties via applied electrical current poses a key, new research topic and technological significance. Studying the spin-orbit-coupled antiferromagnet Ca2RuO4, with 3% Mn doping to weaken the violent first-order transition at 357 K for more robust measurements, we find that a small applied electrical current couples to the lattice by significantly reducing its orthorhombicity and octahedral rotations, concurrently diminishing the 125 K- antiferromagnetic transition and inducing a new, orbital order below 80 K. Our effort to establish a phase diagram reveals a critical regime near a current density of 0.15 A/cm2 that separates the vanishing antiferromagnetic order and the new orbital order. Further increasing current density (> 1 A/cm2) enhances competitions between relevant interactions in a metastable manner, leading to a peculiar glassy behavior above 80 K. The coupling between the lattice and nonequilibrium driven current is interpreted theoretically in terms of t2g orbital occupancies. The current-controlled lattice is the driving force of the observed novel phenomena.