Superconductivity from D3/D7: Holographic Pion Superfluid

TL;DR

This paper demonstrates a holographic superfluid phase transition in a D3/D7 system at finite isospin chemical potential, analyzing conductivity, phase diagram, and superfluid properties within string theory.

Contribution

It introduces a holographic model of superfluidity using D3/D7 branes, revealing a superconductor-like phase transition and detailed properties of the superfluid phase.

Findings

Identified a superfluid phase transition with a delta function in conductivity.

Mapped the phase diagram showing transition order change at critical superfluid velocity.

Analyzed superfluid density, energy gap, and second sound in the holographic model.

Abstract

We show that a D3/D7 system (at zero quark mass limit) at finite isospin chemical potential goes through a superconductor (superfluid) like phase transition. This is similar to a flavored superfluid phase studied in QCD literature, where mesonic operators condensate. We have studied the frequency dependent conductivity of the condensate and found a delta function pole in the zero frequency limit. This is an example of superconductivity in a string theory context. Consequently we have found a superfluid/supercurrent type solution and studied the associated phase diagram. The superconducting transition changes from second order to first order at a critical superfluid velocity. We have studied various properties of the superconducting system like superfluid density, energy gap, second sound etc. We investigate the possibility of the isospin chemical potential modifying the embedding of the flavor branes by checking whether the transverse scalars also condense at low temperature. This however does not seem to be the case.