Spin-Lattice Relaxation in Two-Dimensional Superconducting BKT Transition

TL;DR

This paper demonstrates that the spin-lattice relaxation rate can serve as a direct experimental probe of the Berezinskii-Kosterlitz-Thouless transition in two-dimensional superconductors, revealing coherence effects near the transition temperature.

Contribution

It introduces the use of spin-lattice relaxation rate measurements as a novel method to detect the 2D superconducting BKT transition, including in unconventional pairing states.

Findings

A Hebel-Slichter-like peak appears in $1/T_1T$ near $T_{BKT}$ in $s$-wave superconductors.

No such peak is observed at the pair formation temperature $T_{BCS}$.

The method extends to $d$-wave superconductors, offering a new experimental tool.

Abstract

Two-dimensional superconductors undergo a Berezinskii-Kosterlitz-Thouless transition driven by vortex-antivortex unbinding, yet experimental signatures beyond transport remain limited. Here, we show that the spin-lattice relaxation rate provides a direct probe of this transition. In a 2-dimensional $s$-wave superconductor, $1/T_1T$ develops a Hebel-Slichter-like peak around $T_{\rm{BKT}}$, originating from the emergence of coherence peaks in the density of states, while no peak appears at the pair formation scale $T_{\rm{BCS}}$. We further extend our analysis to the $d$-wave superconductor. Our results highlight spin-lattice relaxation rate as a sensitive tool to detect the superconducting BKT transition and open routes to exploring its manifestation in unconventional pairing states.