Quantum phase transitions of magnetic rotons

TL;DR

This paper investigates quantum phase transitions in magnetic rotons caused by weak spin-orbit coupling, revealing fluctuation-driven first-order transitions, a quantum tricritical point, and non-Fermi liquid behavior, with implications for MnSi.

Contribution

It introduces the concept of magnetic rotons with degenerate minima on a hypersphere and analyzes their role in quantum phase transitions using advanced theoretical methods.

Findings

Identification of magnetic rotons as key excitations in itinerant ferromagnets.

Prediction of fluctuation-driven first-order quantum phase transitions.

Explanation of anomalous high-pressure behavior in MnSi.

Abstract

Due to weak spin-orbit coupling, the magnetic excitations of an itinerant ferromagnet become magnetic rotons, excitations with degenerate minima on a hypersphere at finite wavevector. Using self-consistent Hartree and renormalization group calculations, we study weak fluctuation-driven first-order quantum phase transitions, a quantum tricritical point controlled by anisotropy and the non-Fermi liquid behavior associated with the large phase volume of magnetic rotons. We propose that magnetic rotons are essential for the description of the anomalous high-pressure behavior of the itinerant helical ferromagnet MnSi.