Effective model and Magnetic Properties of the Resistive Electron Quadrupling State

TL;DR

This paper develops an effective model for a resistive four-fermion condensate state that exhibits spontaneous magnetic fields and breaks time-reversal symmetry, revealing potential topological excitations like skyrmions.

Contribution

It introduces a novel effective model akin to the Faddeev-Skyrme model to describe magnetic properties of the four-fermion condensate state.

Findings

The model explains the observed spontaneous magnetic fields.

It predicts the existence of skyrmions as topological excitations.

The state exhibits unconventional magnetic properties.

Abstract

Recent experiments [V.~Grinenko {\it et al.} {Nat. Phys. {\bf 17}, 1254 (2021)}; \url{http://doi.org/10.1038/s41567-021-01350-9}] reported the observation of a condensate of four-fermion composites. This is a resistive state that spontaneously breaks the time-reversal symmetry, leading to unconventional magnetic properties, detected in muon spin rotation experiments and by the appearance of a spontaneous Nernst effect. In this work, we derive an effective model for the four-fermion order parameter that describes the observed spontaneous magnetic fields in this state. We show that this model, which is alike to the Faddeev-Skyrme model can host skyrmions: magnetic-flux-carrying topological excitations.