Strong magnetic instability in correlated metal Bi2Ir2O7

TL;DR

This study reveals that Bi2Ir2O7 exhibits an exotic, strongly correlated metallic state with no magnetic order, characterized by divergent susceptibility, unusual specific heat behavior, and anomalous Hall effects, indicating a novel quantum ground state.

Contribution

The paper provides the first detailed experimental and theoretical analysis of Bi2Ir2O7, demonstrating its unique magnetic and electronic properties driven by spin-orbit coupling and correlations.

Findings

Divergent low-temperature magnetic susceptibility without long-range order

Unusual temperature and field dependence of Hall resistivity

Large Wilson ratio indicating strong electronic correlations

Abstract

The interplay of spin-orbit interactions and electronic correlations dominates the physical properties of pyrochlore iridates, R2Ir2O7 (R = Y, rare earth element), which are typically magnetic insulators. We report an experimental/theoretical study of single-crystal Bi2Ir2O7 where substitutions of Bi for R sensitively tips the balance between competing interactions so as to favor a metallic state with a strongly exchange enhanced paramagnetism. The ground state is characterized by the following features: (1) A divergent low-temperature magnetic susceptibility that indicates no long-range order down to 50 mK; (2) strongly field-dependent coefficients of the low-temperature T- and T3-terms of the specific heat; (3) a conspicuously large Wilson ratio R_W \approx 53.5; and (4) unusual temperature and field dependences of the Hall resistivity that abruptly change below 80 K, without any clear correlation with the magnetic behavior. All these unconventional properties suggest the existence of an exotic ground state in Bi2Ir2O7.