NMR and Specific Heat Investigations in a Strong Electron-Phonon Coupling Superconductor HfV₂^*

Abstract

The nuclear spin lattice relaxation rate 1⁄T₁ of ⁵¹V and specific heat have been measured in a strong electron-phonon coupling superconductor HfV₂. The behavior of 1⁄T₁T between 9.4 K and 100 K in the normal state can be attributed to a sharp narrow d-band with the half width of about 100 K. In the superconducting state, the 1⁄T₁ shows a very small enhancement just below T_c and has the T⁵ dependence well below T_c. These behaviors are interpreted satisfactorily in terms of the ABM model. The value of the electronic specific heat coefficient is about forty times as large as that for Al. The electronic part of the specific heat is proportional to T³ at low temperatures. These facts mean that the superconducting energy gap of HfV₂ is anisotropic and vanishes at points on the Fermi surface.