Electronic specific heat of Tl₂Ba₂CuO_6+δ from 2 K to 300 K for 0≤δ≤0.1

Abstract

Using a high-precision differential technique with a resolution of 1∶10⁴, we have measured the heat capacity of Tl₂Ba₂CuO_6+δ over a temperature range 2–300 K for 0≤δ≤0.1. Anomalies atT _c are seen for all superconducting compositions measured, and the results are consistent with a temperature- andδ-independent normal-state electronic termγ _n∼0.6 mJ/g-at. K². The samples with the largerT _c 's exhibit strong fluctuations in their specific heat, typical of a highly anisotropic 2D superconductor, but there is some evidence that these fluctuations become weaker atT _c falls-consistent with an increase in the coherence length on hole doping. At temperatures below 5 K an upturn in the data is observed which appears to increase in magnitude asT _c falls, correlating with the increase in the Curie term of published susceptibility data.