# Coherent vs incoherent transport in holographic strange insulators

## TL;DR

This paper investigates holographic models of strange insulators, revealing how explicit and spontaneous translational symmetry breaking influence transport mechanisms, with implications for understanding insulating phases in strongly correlated systems.

## Contribution

It distinguishes between explicit and spontaneous translational symmetry breaking in holographic insulators and analyzes their distinct transport properties using a helical model.

## Key findings

- Explicit relevant breaking leads to incoherent transport dominance.
- Pinned spontaneous breaking results in coherent transport being dominant.
- Different mechanisms underlie transport in the two classes of holographic insulators.

## Abstract

Holographic strange metals are known to have a power law resistivity rising with temperature, which is reminiscent of the strange metal phases in condensed matter systems. In some holographic models, however, the exponent of the power law in the resistivity can be negative. In this case one encounters phases with diverging resistivity at zero temperature: holographic strange insulators. These states arise as a result of translational symmetry breaking in the system, which can either be strong explicit and relevant in the IR, or spontaneous, but pinned by a small explicit source. In some regards, one can associate these two classes to the normal band insulators due to the strong ionic potential, and Mott insulator due to the commensurate lock in of the charge density wave. We study different features of these classes on the explicit example of a holographic helical model with homogeneous Bianchy VII type translational symmetry breaking, and uncover the main mechanisms underlying transport in these two cases. We find that while transport in the explicit relevant case is governed by the incoherent conductivity, in the pinned spontaneous case the leading contribution comes from the coherent part.