Spontaneously broken time-reversal symmetry in high-temperature superconductors

TL;DR

This paper proposes a new low-temperature superconducting state with broken time-reversal symmetry characterized by a unique vortex pattern, potentially reconciling conflicting experimental observations in high-temperature superconductors.

Contribution

It introduces a novel superconducting state with spontaneous magnetic fields and a distinctive vortex pattern, advancing understanding of symmetry breaking in high-temperature superconductors.

Findings

Identifies a vortex necklace pattern with fractional vortices.

Shows spectral rearrangement causes surface current states.

Suggests this state explains experimental controversies.

Abstract

Conventional superconductors are strong diamagnets that through the Meissner effect expel magnetic fields. It would therefore be surprising if a superconducting ground state would support spontaneous magnetics fields. Such time-reversal symmetry broken states have been proposed for the high-temperature superconductors, but their identification remains experimentally controversial. Here we show a route to a low-temperature superconducting state with broken time-reversal symmetry that may accommodate currently conflicting experiments. This state is characterised by an unusual vortex pattern in the form of a necklace of fractional vortices around the perimeter of the material, where neighbouring vortices have opposite current circulation. This vortex pattern is a result of a spectral rearrangement of current carrying states near the surfaces.