Berezinskii-Kosterlitz-Thouless transition transport in spin-triplet superconductor

TL;DR

This paper investigates the Berezinskii-Kosterlitz-Thouless (BKT) transitions in 2D spin-triplet superconductors, revealing three types of vortex deconfinement and establishing a transport-based method to detect half-quantum vortices, impacting spintronics.

Contribution

It identifies and characterizes three distinct BKT transitions in 2D spin-triplet superconductors and links them to transport measurements for vortex detection.

Findings

Three types of BKT transitions involving vortices, merons, and half-quantum vortices.

An upper bound on spin supercurrent due to half-quantum vortex transport.

Transport signatures can distinguish different vortex deconfinement transitions.

Abstract

As the spin-triplet superconductivity arises from the condensation of spinful Cooper pairs, its full characterization requires not only charge ordering, but also spin ordering. For a two-dimensional (2D) easy-plane spin-triplet superconductor, this na\"{i}vely seems to suggest the possibility of two distinct Berezinskii-Kosterlitz-Thouless (BKT) phase transitions, one in the charge sector and the other in the spin sector. However, it has been recognized that there are actually three possible BKT transitions, involving the deconfinement of, respectively, the conventional vortices, the merons and the half-quantum vortices with vorticity in both the charge and the spin current. We show how all the transitions can be characterized by the relation between the voltage drop and the spin-polarized current bias. This study reveals that, due to the hitherto unexamined transport of half-quantum vortices, there is an upper bound on the spin supercurrent in a quasi-long range ordered spin-triplet superconductor, which provides a means for half-quantum vortex detection via transport measurements and deeper understanding of fluctuation effects in superconductor-based spintronic devices.