Disorder induced power-law gaps in an insulator-metal Mott transition

TL;DR

This study investigates how disorder influences the insulator-metal transition in Mott insulators, revealing that disorder induces power-law gaps in the density of states, which are a universal feature near the transition.

Contribution

The paper provides experimental evidence that disorder causes V-shaped gaps in Mott insulators, supporting theoretical predictions about the role of disorder in IMTs.

Findings

Disorder induces power-law suppression of the density of states.

Fermi energy pinning persists with increasing disorder.

V-shaped gaps are a universal feature in disordered Mott systems.

Abstract

A correlated material in the vicinity of an insulator-metal transition (IMT) exhibits rich phenomenology and variety of interesting phases. A common avenue to induce IMTs in Mott insulators is doping, which inevitably leads to disorder. While disorder is well known to create electronic inhomogeneity, recent theoretical studies have indicated that it may play an unexpected and much more profound role in controlling the properties of Mott systems. Theory predicts that disorder might play a role in driving a Mott insulator across an IMT, with the emergent metallic state hosting a power law suppression of the density of states (with exponent close to 1; V-shaped gap) centered at the Fermi energy. Such V-shaped gaps have been observed in Mott systems but their origins are as yet unknown. To investigate this, we use scanning tunneling microscopy and spectroscopy to study isovalent Ru substitutions in Sr$_3$(Ir$_{1-x}$Ru$_x$)$_2$O$_7$ which drives the system into an antiferromagnetic, metallic state. Our experiments reveal that many core features of the IMT such as power law density of states, pinning of the Fermi energy with increasing disorder, and persistence of antiferromagnetism can be understood as universal features of a disordered Mott system near an IMT and suggest that V-shaped gaps may be an inevitable consequence of disorder in doped Mott insulators.