Nonequilibrium Orbital Transitions via Applied Electrical Current in Calcium Ruthenate*

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, and its derivative with 3% Mn doping to alleviate the violent first-order transition 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 125K antiferromagnetic transition and inducing a new orbital order below 80K. The phase diagram reveals a critical regime near a current density of 0.15A/cm² that separates the vanishing antiferromagnetic order and the new orbital order. Further increasing current density (> 1A/cm²) enhances competitions between relevant interactions in a metastable manner, leading to a peculiar glassy behavior above 80K. The coupling between the lattice and nonequilibrium driven current is interpreted theoretically in terms of t_2g orbital occupancies. The current-controlled lattice is the driving force of the observed novel phenomena. Finally, we note that current-induced diamagnetism is not discerned in pure and slightly doped Ca₂RuO₄.