The types of Mott insulator

TL;DR

This paper classifies Mott insulators into two types based on their doping responses, highlighting their phase transition behaviors and analogies with superconductors, and discusses how broken symmetry influences their classification.

Contribution

It introduces a classification scheme for Mott insulators into Type I and Type II, based on their phase transition characteristics and symmetry properties.

Findings

Type I Mott insulators undergo first-order phase transitions.

Type II Mott insulators exhibit continuous doping transitions.

Broken symmetry increases the likelihood of a Mott insulator being Type I.

Abstract

There are two classes of Mott insulators in nature, distinguished by their responses to weak doping. With increasing chemical potential, Type I Mott insulators undergo a first order phase transition from the undoped to the doped phase. In the presence of long-range Coulomb interactions, this leads to an inhomogeneous state exhibiting ``micro-phase separation.'' In contrast, in Type II Mott insulators charges go in continuously above a critical chemical potential. We show that if the insulating state has a broken symmetry, this increases the likelihood that it will be Type I. There exists a close analogy between these two types of Mott insulators and the familiar Type I and Type II superconductors.