A Unique Crystal Structure of Ca$_2$RuO$_4$ in the Current Stabilized Semi-Metallic State

TL;DR

This study reveals a unique non-equilibrium crystal structure in Ca$_2$RuO$_4$ under current stabilization, leading to a semi-metallic state with strong diamagnetism and distinct electronic properties, different from equilibrium phases.

Contribution

It identifies a new crystal structure in Ca$_2$RuO$_4$ stabilized by current, providing insights into its electronic and magnetic behavior distinct from known equilibrium phases.

Findings

Distinct crystal structure in non-equilibrium state

Homogeneous non-equilibrium behavior with suppressed magnetic order

Semi-metallic state with partially gapped Fermi surface

Abstract

The electric-current stabilized semi-metallic state in the quasi-two-dimensional Mott insulator Ca$_2$RuO$_4$ exhibits an exceptionally strong diamagnetism. Through a comprehensive study using neutron and X-ray diffraction, we show that this non-equilibrium phase assumes a crystal structure distinct from those of equilibrium metallic phases realized in the ruthenates by chemical doping, high pressure and epitaxial strain, which in turn leads to a distinct electronic band structure. Dynamical mean field theory calculations based on the crystallographically refined atomic coordinates and realistic Coulomb repulsion parameters indicate a semi-metallic state with partially gapped Fermi surface. Our neutron diffraction data show that the non-equilibrium behavior is homogeneous, with antiferromagnetic long-range order completely suppressed. These results provide a new basis for theoretical work on the origin of the unusual non-equilibrium diamagnetism in Ca$_2$RuO$_4$.