Specific heat of 2H NbSe2

Abstract

The specific heats of four samples of 2H NbSe₂ have been measured in the temperature range from 1 to 54 K. No anomalous behavior was found near 40 K where x‐ray, NMR, and Hall‐effect measurements have indicated the presence of a phase transition. An upper limit of 0.3 J/mole K has been placed on the magnitude of any anomaly in the heat capacity associated with this transition. Measurements of high‐purity stoichiometric 2H NbSe₂ sample gave a superconducting transition temperature of 7.23 K, a specific heat jump (ΔC) in zero field of 240 mJ/mole K, and a Debye temperature of 204 K. A deviation from the usual T³ behavior for the lattice contribution to the heat capacity was observed and assumed to be due to the two‐dimensional layer structure of the compound. Our best estimate for the electronic coefficient of specific heat (γ) is about 10±5 mJ/mole K². Based on the values for T_c and ΔC, the value for γ calculated from BCS theory is 23 mJ/mole K² for 2H NbSe₂ which is in disagreement with our estimated value for γ by a factor of 2.