On the possibility of fast vortices in the cuprates: A vortex plasma model analysis of THz conductivity and diamagnetism in La$_{2-x}$Sr$_{x}$CuO$_4$

TL;DR

This study investigates fluctuation superconductivity in underdoped La$_{2-x}$Sr$_{x}$CuO$_4$ using THz spectroscopy and diamagnetism measurements, revealing vortices with unexpectedly high diffusion constants or alternative non-superconducting origins of diamagnetism.

Contribution

The paper introduces a vortex-plasma model analysis showing that observed diamagnetism implies vortices with anomalously large diffusion constants or non-superconducting contributions.

Findings

Vortices must have diffusion constants over 100 times larger than Bardeen-Stephen estimate.

Diamagnetism may originate from non-superconducting sources.

Results challenge conventional vortex dynamics in underdoped cuprates.

Abstract

We present measurements of the fluctuation superconductivity in an underdoped thin film of La$_{1.905}$Sr$_{0.095}$CuO$_4$ using time-domain THz spectroscopy. We compare our results with measurements of diamagnetism in a similarly doped crystal of La$_{2-x}$Sr$_x$CuO$_4$. We show through a vortex-plasma model that if the fluctuation diamagnetism solely originates in vortices, then they must necessarily exhibit an anomalously large vortex diffusion constant, which is more than two orders of magnitude larger than the Bardeen-Stephen estimate. This points to either the extremely unusual properties of vortices in the under-doped d-wave cuprates or a contribution to the diamagnetic response that is not superconducting in origin.