High-order coupling as a driver for Mott insulating behavior in Holography

TL;DR

This paper develops a holographic model with higher-order couplings to simulate Mott insulator behavior, capturing metal-insulator transitions, soft gaps, and multi-peak AC conductivity structures similar to experimental observations.

Contribution

It introduces a simple holographic framework with higher-order interactions that reproduces key features of Mott insulators, including transition phenomena and spectral characteristics.

Findings

Reproduces metal-insulator transition in holography

Observes soft gap and multi-peak structures in AC conductivity

Matches numerical results with sum rules and DC conductivity

Abstract

We construct a simple holographic model incorporating higher-order coupling terms for electron self-interactions. It can exhibit typical behavior of a Mott insulator, including a metal-insulator transition and a decrease in DC conductivity with the increase of charge density. In the analysis of AC conductivity, a soft gap is generally observed. Notably, when the DC conductivity approaches zero, the AC conductivity reveals a multi-peak structure, which can be attributed to the Mott and charge-transfer gaps observed experimentally in transition metals. With the increase of DC conductivity, the multi-peak structure gradually reverts to soft-gap behavior or even metallic conductivity. The accuracy of the numerical result is guaranteed by $\sigma(\omega\to 0)=\sigma_{DC}$ and sum rules.