Holographic s+p superconductors with axion induced translation symmetry breaking

Abstract

We construct a holographic model for an s+p superconductor with axion-induced translation symmetry breaking within the framework of gauge/gravity duality, working in the probe limit. The equations of motion are solved numerically to investigate the influence of the parameter $k/T$ on the competition and coexistence between the s-wave and p-wave orders. We find that increasing $k/T$ suppresses the thermodynamic stability of both the single condensate s-wave and p-wave solutions. With the $k-\mu$ phase diagram and the condensate curves, we see that the region dominated by the single condensate p-wave phase gradually decreases with the increasing of $k/T$, finally leaving only the single condensate s-wave phase in the large $k/T$ region, which is explained by the grand potential curves showing a slower decreasing of the thermodynamic stability for the s-wave solution than that for the p-wave solution. Furthermore, a larger minimum ratio of the charges $q_p/q_s$ is required to stabilize the s+p coexistent phase as $k/T$ increases, and we determine the precise dependence of this critical ratio on $k/T$. Finally, our study of the optical conductivity reveals that the gap frequency increases with $k/T$. A characteristic kink, associated with the s+p coexistent phase, is identified in the dependence of gap frenquency on $k/T$, which could serve as a potential experimental signature for detecting multi-condensate superconductivity.

7 pages, 6 figures