Polarized solutions and Fermi surfaces in holographic Bose-Fermi systems

TL;DR

This paper uses holography to explore the ground states of a system with interacting bosons and fermions at finite density, revealing coexistence of particle and antiparticle fluids, Fermi surfaces, and signs of superconductivity.

Contribution

It introduces a holographic model with scalar and fermionic fields that exhibits novel solutions including antiparticle fluids and coexisting phases, advancing understanding of strongly correlated systems.

Findings

Thermodynamically favored antiparticle fermion solutions.

Presence of electron-like and hole-like Fermi surfaces.

Scalar condensate destroys low-momentum Fermi surfaces, indicating superconductivity.

Abstract

We use holography to study the ground state of a system with interacting bosonic and fermionic degrees of freedom at finite density. The gravitational model consists of Einstein-Maxwell gravity coupled to a perfect fluid of charged fermions and to a charged scalar field which interact through a current-current interaction. When the scalar field is non-trivial, in addition to compact electron stars, the screening of the fermion electric charge by the scalar condensate allows the formation of solutions where the fermion fluid is made of antiparticles, as well as solutions with coexisting, separated regions of particle-like and antiparticle-like fermion fluids. We show that, when the latter solutions exist, they are thermodynamically favored. By computing the two-point Green function of the boundary fermionic operator we show that, in addition to the charged scalar condensate, the dual field theory state exhibits electron-like and/or hole-like Fermi surfaces. Compared to fluid-only solutions, the presence of the scalar condensate destroys the Fermi surfaces with lowest Fermi momenta. We interpret this as a signal of the onset of superconductivity.