Thermodynamic properties in the normal and superconducting states of Na(x)CoO(2)*yH(2)O powder measured by heat capacity experiments

TL;DR

This study measures the heat capacity of Na(x)CoO(2)*yH(2)O to analyze its superconducting properties, comparing models with and without line nodes, revealing a possible fully gapped or nodal gap structure.

Contribution

It provides a thermodynamically consistent analysis of heat capacity data, distinguishing between fully gapped and nodal superconducting gap structures in Na(x)CoO(2)*yH(2)O.

Findings

Data suggest about 55% superconducting volume if fully gapped.

Line nodes in the gap are compatible with 100% superconductivity.

Electronic heat capacity was separated from lattice contributions accurately.

Abstract

The heat capacity of superconducting Na(x)CoO(2)*yH(2)O was measured and the data are discussed based on three different models: The thermodynamic Ginzburg-Landau model, the BCS theory, and a model including the effects of line nodes in the superconducting gap function. The electronic heat capacity is separated from the lattice contribution in a thermodynamically consistent way maintaining the entropy balance of superconducting and normal states at the critical temperature. It is shown that for a fully gapped superconductor the data can only be explained by a reduced (about 55 %) superconducting volume fraction. The data are compatible with 100 % superconductivity in the case where line nodes are present in the superconducting gap function.