Exciton-driven quantum phase transitions in holography

TL;DR

This paper investigates quantum phase transitions in holography driven by fermionic deformations, revealing various critical behaviors and the influence of magnetic fields on non-Fermi liquid states.

Contribution

It introduces a holographic model showing how fermionic double-trace deformations induce quantum critical points with diverse transition types and magnetic field effects.

Findings

Identification of Berezinskii-Kosterlitz-Thouless and second order transitions.

Magnetic field enhances order parameter in non-Fermi liquids.

Connection to experimental stabilization of non-Fermi liquids.

Abstract

We study phase transitions driven by fermionic double-trace deformations in gauge-gravity duality. Both the strength of the double trace deformation and the infrared conformal dimension/self-energy scaling of the quasiparticle can be used to decrease the critical temperature to zero, leading to a line of quantum critical points. The self-energy scaling is controlled indirectly through an applied magnetic field and the quantum phase transition naturally involves the condensation of a fermion bilinear which models the spin density wave in an antiferromagnetic state. The nature of the quantum critical points depends on the parameters and we find either a Berezinskii-Kosterlitz-Thouless-type transition or one of two distinct second order transitions with non-mean field exponents. One of these is an anomalous branch where the order parameter of constituent non-Fermi liquid quasiparticles is enhanced by the magnetic field. Stabilization of ordered non-Fermi liquids by a strong magnetic field is observed in experiments with highly oriented pyrolytic graphite.