Zero Temperature Limit of Holographic Superconductors

TL;DR

This paper analyzes the zero-temperature behavior of holographic superconductors, showing the absence of a hard gap in conductivity and exploring the ground state structure through analytic and numerical methods.

Contribution

It provides an analytic proof that the real part of conductivity remains nonzero at zero temperature and constructs the gravitational duals of the ground states for various condensates.

Findings

No hard gap in low-frequency conductivity at zero temperature

Infrared theories can have emergent conformal or Poincare symmetry

Horizon area approaches zero in the extremal limit

Abstract

We consider holographic superconductors whose bulk description consists of gravity minimally coupled to a Maxwell field and charged scalar field with general potential. We give an analytic argument that there is no "hard gap": the real part of the conductivity at low frequency remains nonzero (although typically exponentially small) even at zero temperature. We also numerically construct the gravitational dual of the ground state of some holographic superconductors. Depending on the charge and dimension of the condensate, the infrared theory can have emergent conformal or just Poincare symmetry. In all cases studied, the area of the horizon of the dual black hole goes to zero in the extremal limit, consistent with a nondegenerate ground state.