Impure AdS/CFT

TL;DR

This paper investigates how impurities affect momentum relaxation in a strongly coupled conformal field theory using AdS/CFT, revealing different behaviors for magnetic and electric impurities and analyzing transport responses like the Nernst effect.

Contribution

It introduces a holographic model of impurity-induced momentum relaxation in a strongly coupled CFT, highlighting the effects of magnetic and electric impurities and their impact on relaxation times.

Findings

Magnetic impurities suppress momentum relaxation with increasing magnetic field or charge density.

Electric impurities cause a sharp increase in relaxation rate near a critical field and density.

The Nernst response in the impure theory shows similarities to experimental observations in superconductors.

Abstract

We study momentum relaxation due to dilute, weak impurities in a strongly coupled CFT, a truncation of the M2 brane theory. Using the AdS/CFT correspondence, we compute the relaxation time scale as a function of the background magnetic field B and charge density \rho. The theory admits two different types of impurities. We find that for magnetic impurities, momentum relaxation due to the impurity is suppressed by a background B or \rho. For electric impurities, due to an underlying instability in the theory towards an ordered phase, the inverse relaxation time scale increases dramatically near \sqrt{B^2 + \rho^2/\sigma^2_0} \sim 21 T^2. We compute the Nernst response for the impure theory, and comment on similarities with recent measurements in superconductors.