Scanning tunneling microscopy and spectroscopy on cracked surfaces of superconducting CeRu₂

Scanning tunneling microscopy and scanning tunneling spectroscopy measurements have been performed on a single crystal of CeRu₂ down to 2.2 K under a magnetic field up to 2.0 T. The sample surfaces for the measurements are prepared by cutting or cracking the single crystal at 4.2 K. The vortex lattice has been imaged by mapping the quasi-particle density of states at the Fermi energy on the surface. We have observed that the surface has been covered with microstructures a few nm in diameter. These microstructures are characteristic of the surface when the sample is cut or cracked at low temperature.