Vortex lattice and quasiparticle density of states in CeRu2 studied by scanning tunneling spectroscopy

Scanning tunneling microscopy (STM) and spectroscopy (STS) measurements hale been performed on an intermetallic compound CeRu2 down to 2.2 K. Vacuum tunneling spectra have been measured on the surface prepared by cracking the sample in helium gas at 4.2 K. The shape and temperature dependence of the quasiparticle density of stales, N-s(E, r), have been well interpreted in terms of s-wave BCS superconductors. In magnetic fields, the hexagonal vortex lattice has been imaged by measurements of N-s(E = 0, r) up to 2 T. This is the first observation of the vortex lattice by STS in heavy-fermion superconductors.