Effects of charge doping on Mott insulator with strong spin-orbit coupling, Ba$_2$NaOsO$_6$

TL;DR

This study explores how charge doping influences the electronic and magnetic phases of the Mott insulator Ba$_2$NaOsO$_6$, revealing phase transitions and symmetry breaking driven by multipolar order.

Contribution

It provides a detailed phase diagram showing doping-induced magnetic and symmetry changes in a complex spin-orbit coupled Mott insulator.

Findings

Insulating magnetic ground state transitions from canted antiferromagnet to Néel order above 10% doping.

A broken local point symmetry phase extends over a significant doping range.

Symmetry breaking is driven by multipolar, likely antiferro-quadrupolar, order.

Abstract

The effects of doping on the electronic evolution of the Mott insulating state have been extensively studied in efforts to understand mechanisms of emergent quantum phases of materials. The study of these effects becomes ever more intriguing in the presence of entanglement between spin and orbital degrees of freedom. Here, we present a comprehensive investigation of charge doping in the double perovskite Ba$_2$NaOsO$_6$, a a complex Mott insulator where such entanglement plays an important role. We establish that the insulating magnetic ground state evolves from canted antiferromagnet (cAF)to N\'eel order for dopant levels exceeding ~ 10 %. Furthermore, we determine that a broken local point symmetry (BLPS) phase, precursor to the magnetically ordered state, occupies an extended portion of the (H-T) phase diagram with increased doping. This finding reveals that the breaking of the local cubic symmetry is driven by a multipolar order, most-likely of the antiferro-quadrupolar type.