Nature of the quantum phase transition to a spin-nematic phase

TL;DR

This paper demonstrates that the quantum phase transition to a spin-nematic phase in metallic non-s-wave ferromagnets is typically first order due to coupling with soft electronic modes, with implications for phase diagram features.

Contribution

It provides a generalized mean-field theory showing the fluctuation-induced first-order transition in spin nematics and predicts tricritical wings in the phase diagram.

Findings

Transition is generically first order due to electronic mode coupling.

Tricritical wings appear in spatially varying magnetic fields.

The theory explicitly models p-wave spin nematic transitions.

Abstract

It is shown that the quantum phase transition in metallic non-s-wave ferromagnets, or spin nematics, is generically of first order. This is due to a coupling of the order parameter to soft electronic modes that play a role analogous to that of the electromagnetic vector potential in a superconductor, which leads to a fluctuation-induced first-order transition. A generalized mean-field theory for the p-wave case is constructed that explicitly shows this effect. Tricritical wings are predicted to appear in the phase diagram in a spatially varying magnetic field, but not in a homogeneous one.