Specific heat of unconventional superconductivity in NaxCoO2-yH2O

TL;DR

This study investigates the low-temperature specific heat of NaxCoO2-yH2O, revealing evidence of bulk superconductivity with line nodal order parameters and complex phase transition behavior.

Contribution

It provides comprehensive experimental data on specific heat and identifies line nodal superconductivity in NaxCoO2-yH2O, highlighting unique phase transition features.

Findings

Sharp anomaly at 4.7 K indicating bulk superconductivity

Presence of T^2 term suggesting line nodal order parameter

Superconducting volume fraction estimated at 26.6%

Abstract

Comprehensive studies of the low-temperature specific heat C(T,H) in NaxCoO2-yH2O are presented. At H=0, a very sharp anomaly was observed at T=4.7 K indicating the existence of bulk superconductivity. There exists the T^2 term in C(T,H=0) in the superconducting state manifesting the line nodal superconducting order parameter. The superconducting volume fraction is estimated to be 26.6 % based on the consideration of entropy conservation at Tc for the second-order superconducting phase transition. An abrupt change of the slope in Tc(H) was observed. Possible scenarios such as the multiple phase transitions in the mixed state are discussed.