Stability of topological defects in chiral superconductors: London theory

TL;DR

This paper analyzes the stability and behavior of topological defects like domain walls and vortices in chiral superconductors using London theory, revealing conditions for their formation and implications for mesoscopic samples and materials like Sr2RuO4.

Contribution

It provides a theoretical framework for understanding the thermodynamic stability and entry conditions of topological defects in chiral superconductors, including effects in mesoscopic samples.

Findings

Small fields favor single-domain configurations.

Critical fields for defect entry are calculated.

Behavior of soft domain walls in mesoscopic samples differs from bulk.

Abstract

This paper examines thermodynamic stability of chiral domain walls and vortices - topological defects which can exist in chiral superconductors. Using London theory it is demonstrated that at sufficiently small applied and chiral fields the existence of domain walls and vortices in the sample is not favored and the sample's configuration is a single domain. The particular chirality of the single-domain configuration is neither favored nor disfavored by the applied field. Increasing the field leads to an entry of a domain wall loop or a vortex into the sample. Formation of a straight domain wall is never preferred in equilibrium. Values of the entry (critical) fields for both types of defects, as well as the equilibrium size of the domain wall loop, are calculated. We also consider a mesoscopic chiral sample and calculate its zero-field magnetization, susceptibility and a change in the magnetic moment due to a vortex or a domain wall entry. We show that in a case of a soft domain wall whose energetics is dominated by the chiral current (and not by the surface tension) its behavior in mesoscopic samples is substantially different from that in the bulk case and can be used for a controllable transfer of edge excitations. The applicability of these results to Sr2RuO4 - a tentative chiral superconductor - is discussed.