Spin-orbit tuned metal-insulator transitions in single-crystal Sr2Ir1-xRhxO4 (0\leqx\leq1)

TL;DR

This study explores how substituting Rh for Ir in Sr2IrO4 tunes the spin-orbit interaction, leading to a complex phase diagram with transitions from insulator to metal and back, revealing the critical role of spin-orbit coupling.

Contribution

It provides a detailed phase diagram of Sr2Ir1-xRhxO4 showing how Rh doping modulates spin-orbit interaction and induces multiple electronic and magnetic phase transitions.

Findings

Light Rh doping suppresses magnetic order and resistivity.

Heavier Rh doping causes localization and reentrant insulating behavior.

Comparison with Ru doping highlights different transition mechanisms.

Abstract

Sr2IrO4 is a magnetic insulator driven by spin-orbit interaction (SOI) whereas the isoelectronic and isostructural Sr2RhO4 is a paramagnetic metal. The contrasting ground states have been shown to result from the critical role of the strong SOI in the iridate. Our investigation of structural, transport, magnetic and thermal properties reveals that substituting 4d Rh4+ (4d5) ions for 5d Ir4+(5d5) ions in Sr2IrO4 directly reduces the SOI and rebalances the competing energies so profoundly that it generates a rich phase diagram for Sr2Ir1-xRhxO4 featuring two major effects: (1) Light Rh doping (0\leqx\leq0.16) prompts a simultaneous and precipitous drop in both the electrical resistivity and the magnetic ordering temperature TC, which is suppressed to zero at x = 0.16 from 240 K at x=0. (2) However, with heavier Rh doping (0.24< x<0.85 (\pm0.05)) disorder scattering leads to localized states and a return to an insulating state with spin frustration and exotic magnetic behavior that only disappears near x=1. The intricacy of Sr2Ir1-xRhxO4 is further highlighted by comparison with Sr2Ir1-xRuxO4 where Ru4+(4d4) drives a direct crossover from the insulating to metallic states.