Quantum phase transitions in holographic models of magnetism and superconductors

TL;DR

This paper models quantum phase transitions in holographic systems, revealing how antiferromagnetic and ferromagnetic phases emerge and transition at zero temperature, with implications for understanding strongly correlated materials.

Contribution

It introduces a holographic model of antiferromagnetism with quantum phase transitions driven by tuning the conformal dimension, including spin wave characterizations.

Findings

Quantum phase transition of BKT type achieved by tuning UV conformal dimension.

Antiferromagnetic phase exhibits linear spin wave dispersion.

Ferromagnetic phase shows quadratic spin wave dispersion.

Abstract

We study a holographic model realizing an "antiferromagnetic" phase in which a global SU(2) symmetry representing spin is broken down to a U(1) by the presence of a finite electric charge density. This involves the condensation of a neutral scalar field in a charged AdS black hole. We observe that the phase transition for both neutral and charged (as in the standard holographic superconductor) order parameters can be driven to zero temperature by a tuning of the UV conformal dimension of the order parameter, resulting in a quantum phase transition of the Berezinskii-Kosterlitz-Thouless type. We also characterize the antiferromagnetic phase and an externally forced ferromagnetic phase by showing that they contain the expected spin waves with linear and quadratic dispersions respectively.