Destruction of the Mott Insulating Ground State of Ca_2RuO_4 by a Structural Transition

TL;DR

This study reveals a first-order phase transition in Ca_2RuO_4 at 357 K, where a structural change causes the collapse of its Mott insulating state without magnetic ordering, highlighting a unique insulator-to-metal transition.

Contribution

It demonstrates that a structural transition can destroy the Mott insulating phase in Ca_2RuO_4 without magnetic order, providing new insights into phase transitions in correlated materials.

Findings

Discontinuous decrease in resistivity at T_M=357 K

Structural transition from orthorhombic to tetragonal phase

Loss of Mott insulating state without magnetic order

Abstract

We report a first-order phase transition at T_M=357 K in single crystal Ca_2RuO_4, an isomorph to the superconductor Sr_2RuO_4. The discontinuous decrease in electrical resistivity signals the near destruction of the Mott insulating phase and is triggered by a structural transition from the low temperature orthorhombic to a high temperature tetragonal phase. The magnetic susceptibility, which is temperature dependent but not Curie-like decreases abruptly at TM and becomes less temperature dependent. Unlike most insulator to metal transitions, the system is not magnetically ordered in either phase, though the Mott insulator phase is antiferromagnetic below T_N=110 K.