Pressure and magnetic-field effects on metal-insulator transitions of bulk and domain-wall states in pyrochlore iridates

TL;DR

This study investigates how pressure and magnetic fields influence metal-insulator transitions in pyrochlore iridates, revealing the roles of electron correlation, magnetic order, and domain-wall states in these complex materials.

Contribution

It systematically explores the effects of ionic radius, pressure, and magnetic field on metal-insulator transitions and domain-wall states in pyrochlore iridates, highlighting new insights into their phase behavior.

Findings

Metal-insulator transitions are driven by ionic radius and pressure.

Metallic states appear between paramagnetic and antiferromagnetic insulating phases.

Magnetic fields induce metal-insulator transitions and reveal topological states.

Abstract

We have explored the critical metal-insulator phenomena for pyrochlore-type $R_2$Ir$_2$O$_7$, in which electron correlation strength and magnetic configuration are systematically controlled by varying the average rare-earth ionic radius ($R$=Nd$_{1-x}$Pr$_{x}$ and Sm$_{y}$Nd$_{1-y}$), external pressure, and magnetic field. Metal-insulator transitions in bulk are caused by increasing $x$ or tuning external pressure, indicating that the effective electron correlation is responsible for the transition. The metallic state intervenes between the paramagnetic insulating and antiferromagnetically ordered insulating phases for \SNIO ($y$=0.7-0.9), reminiscent of the first-order Mott transition. Furthermore, the metal-to-insulator crossover is observed (around $y$=0.7) for the charge transport on magnetic domain walls in the insulating bulk. An application of magnetic field also drives metal-insulator transitions for \NPIO in which a variety of exotic topological quantum states are potentially realized.