Universal Heat Conduction in YBa_2Cu_3O_6.9

TL;DR

This study demonstrates universal heat conduction in YBa_2Cu_3O_6.9, showing a residual linear thermal conductivity at low temperatures that is unaffected by Zn impurities, supporting theories of d-wave superconductivity.

Contribution

It provides experimental evidence for universal heat conduction in a cuprate superconductor, confirming theoretical predictions for d-wave symmetry.

Findings

Residual linear thermal conductivity is independent of Zn impurity concentration.

The observed behavior aligns with d-wave gap symmetry calculations.

Supports the theory of universal heat conduction in unconventional superconductors.

Abstract

The thermal conductivity of YBa_2Cu_3O_6.9 was measured at low temperatures in untwinned single crystals with concentrations of Zn impurities from 0 to 3% of Cu. A linear term kappa_0/T = 0.19 mW/K^2.cm is clearly resolved as T -> 0, and found to be virtually independent of Zn concentration. The existence of this residual normal fluid strongly validates the basic theory of transport in unconventional superconductors. Moreover, the observed universal behavior is in quantitative agreement with calculations for a gap function of d-wave symmetry.