Magnetic Quantum Phase Transitions in a Clean Dirac Metal

TL;DR

This paper investigates quantum phase transitions in clean Dirac metals with strong spin-orbit coupling, revealing that fermionic soft modes generally induce first-order transitions across various magnetic phases, highlighting the role of chirality.

Contribution

It demonstrates that fermionic soft modes cause first-order quantum phase transitions in Dirac metals, a surprising result given the suppressive effect of spin-orbit scattering.

Findings

First-order transitions occur in multiple magnetic phases due to soft mode coupling.

Chirality plays a crucial role in the mechanism of transition.

Possible exception in certain gapless Dirac systems.

Abstract

We consider clean Dirac metals where the linear band crossing is caused by a strong spin-orbit interaction, and study the quantum phase transitions from the paramagnetic phase to various magnetic phases, including homogeneous ferromagnets, ferrimagnets, canted ferromagnets, and magnetic nematics. We show that in all of these cases the coupling of fermionic soft modes to the order parameter generically renders the quantum phase transition first order, with certain gapless Dirac systems providing a possible exception. These results are surprising since a strong spin-orbit scattering suppresses the mechanism that causes the first order transition in ordinary metals. The important role of chirality in generating a new mechanism for a first-order transition is stressed.