Visualization of vortex sheets and half quantum vortices in the chiral odd-parity superconductor UPt$_{3}$

TL;DR

This paper visualizes vortex structures in the unconventional superconductor UPt$_{3}$, revealing half-quantum vortices and domain walls, supporting theories of chiral superconductivity with complex order parameters.

Contribution

It provides direct experimental imaging of half-quantum vortices and domain walls in UPt$_{3}$, confirming theoretical predictions of chiral superconductivity.

Findings

Observation of mobile half-quantum vortices

Detection of domain wall-like magnetic contrast lines

Agreement with chiral superconductivity theories

Abstract

Superconductivity is characterized by vanishing electrical resistance and magnetic flux expulsion. For conventional type II superconductors, the magnetic flux expulsion is incomplete in an applied magnetic field above a critical value and magnetic flux penetrates the bulk of the superconductor in discrete quantized magnetic flux tubes (vortices), each carrying a single quantum of flux (h/2e). Investigating the unconventional superconductor UPt$_{3}$ with a scanning superconducting quantum interference device (SQUID) microscope, we observed mobile half-quantum vortices together with one quantum vortices. Cooling the material under a higher magnetic field revealed the presence of lines of magnetic contrast resembling domain walls. These observations agree with theoretical predictions for chiral superconductivity with a two dimensional complex order-parameter with sheets of half-quantum vortices separating domains of opposite order-parameter chirality.