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

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 numerical reliability is confirmed by the agreement between zero-frequency AC and DC conductivities.

Figures (10)

• Figure 1: Fig.\ref{['chargeMott1']}, adapted from roy2019mott, show mechanism of Mott insulator, involving Hubbard band splitting and charge order, corresponds to the characteristic double-peak behavior observed experimentally of \ref{['ACCon1']}, reproduced from moon2009temperature.
• Figure 2: The negative conductivity region diagram when different parameters are fixed.
• Figure 3: The DC conductivity varies with charge density $q$. It is observed that both an increase in coupling strength $\mathcal{J}$ and a decrease in temperature $T$ enhance the effect of conductivity reduction as charge density $q$ increases.
• Figure 4: The observation of negative DC conductivity suggests the opening of an energy gap.
• Figure 5: The DC conductivity exhibits a metal-insulator transition as temperature changes.