Evidence for field-induced excitations in low-temperature thermal conductivity of Bi_2Sr_2CaCu_2O_8

TL;DR

This study investigates how magnetic fields affect the low-temperature thermal conductivity of Bi_2Sr_2CaCu_2O_8, revealing field-induced excitations and challenging the fully gapped state hypothesis.

Contribution

It provides experimental evidence of field-induced excitations in thermal conductivity, supporting theories of Doppler shift effects over fully gapped state models.

Findings

Thermal conductivity increases below 1K with magnetic field.

Behavior inconsistent with a field-induced fully gapped state.

Supports Doppler shift model for quasiparticle spectrum enhancement.

Abstract

The thermal conductivity ,$\kappa$, of Bi_2Sr_2CaCu_2O_8 was studied as a function of magnetic field. Above 5 K, after an initial decrease, $\kappa(H)$ presents a kink followed by a plateau, as recently reported by Krishana et al.. By contrast, below 1K, the thermal conductivity was found to \emph{increase} with increasing field. This behavior is indicative of a finite density of states and is not compatible with the existence of a field-induced fully gapped $d_{x^{2}-y^{2}}+id_{xy}$ state which was recently proposed to describe the plateau regime. Our low-temperature results are in agreement with recent works predicting a field-induced enhancement of thermal conductivity by Doppler shift of quasi-particle spectrum.