Zero Temperature Holographic Superfluids with Two Competing Orders

TL;DR

This paper explores zero temperature holographic superfluids with two competing orders, revealing a rich phase diagram, superfluid phases, and phase transition signatures through optical conductivity and sound speed analysis.

Contribution

It introduces the first study of coexistent superfluid phases in a zero temperature holographic model with two competing orders and constructs their phase diagram.

Findings

Identification of coexistent superfluid phase in the AdS soliton background.

Optical conductivity pole indicates superfluid phase and its relation to superfluid density.

Sound speed behavior reveals phase transition points and saturation at high chemical potential.

Abstract

We initiate the investigation of the zero temperature holographic superfluids with two competing orders, where besides the vacuum phase, two one band superfluid phases, the coexistent superfluid phase has also been found in the AdS soliton background for the first time. We construct the complete phase diagram in the $e-\mu$ plane by numerics, which is consistent with our qualitative analysis. Furthermore, we calculate the corresponding optical conductivity and sound speed by the linear response theory. The onset of pole of optical conductivity at $\omega=0$ indicates that the spontaneous breaking phase always represents the superfluid phase, and the residue of pole is increased with the chemical potential, which is consistent with the fact that the particle density is essentially the superfluid density for zero temperature superfluids. In addition, the resulting sound speed demonstrates the non-smoothness at the critical points as the order parameter of condensate, which indicates that the phase transitions can also be identified by the behavior of sound speed. Moreover, as expected from the boundary conformal field theory, the sound speed saturates to $\frac{1}{\sqrt{2}}$ at the large chemical potential limit for our two band holographic superfluid model.