Vortex fluctuations in underdoped Bi2Sr2CaCu2O8+d crystals

TL;DR

This study investigates vortex thermal fluctuations in heavily underdoped Bi2Sr2CaCu2O8+d crystals using Josephson plasma resonance, revealing how thermal fluctuations influence vortex behavior and phase correlations.

Contribution

It provides new measurements of penetration depth, anisotropy, and vortex wandering length, linking thermal fluctuations to vortex dissociation in underdoped cuprates.

Findings

Thermal fluctuations cause vortex dissociation at the first order transition.

Penetration depth along the c-axis is 229 micrometers.

Anisotropy ratio is 600.

Abstract

Vortex thermal fluctuations in heavily underdoped Bi2Sr2CaCu2O8+d (Tc=69.4 K) are studied using Josephson plasma resonance (JPR). From the data in zero magnetic field, we obtain the penetration depth along the c-axis, lambda_{L,c}(0) = 229 micrometers and the anisotropy ratio gamma(0) = 600. The low plasma frequency allows us to study phase correlations over the whole vortex solid (Bragg-glass) state. The JPR results yield a wandering length r_{w} of vortex pancakes. The temperature dependence of r_{w} as well as its increase with applied dc magnetic field can only be explained by the renormalization of the tilt modulus by thermal fluctuations, and suggest the latter is responsible for the dissociation of the vortices at the first order transition.