Experimental Indications of a BCS Behaviour in Superconducting Diamond

Abstract

AbstractThis special issue of physica status solidi which was guest‐edited by Satoshi Koizumi (National Institute for Materials Science, Tsukuba, Japan), Christoph E. Nebel (Diamond Research Center, Tsukuba, Japan), and Milos Nesladek (CEA‐LIST, Gif sur Yvette, France) presents 10 Review Articles covering different areas of CVD Diamond research.The cover picture was taken from the article by Sacépé et al. [1]. The authors present a scanning tunneling spectroscopy study of superconducting single‐crystalline heavily boron‐doped diamond providing an experimental evidence for BCS behaviour. When a perpendicular magnetic field is applied to a superconducting boron‐doped diamond film, vortices penetrate the sample, each carrying one quantum flux. In their centre, the superconductivity is washed out on a length scale equal to the superconducting coherence length ξs. The figures show the electronic Density of States (DOS) measured with a scanning tunnelling microscope at 50 mK along a line crossing the centre of a such a vortex. Outside the vortex core which extends between the two arrows, the DOS presents a gap at the Fermi level (V = 0) and two coherence peaks characteristic of a superconducting DOS. The measured DOS inside the vortex core reveals in addition numerous localized resonances, at positions pointed out by the black arrows on the two‐dimensional view. For clean superconductors, quasi‐particles are expected to form localized states inside the vortex cores at energies close to the Fermi level. Here, although boron‐doped diamond films are in the dirty limit, localized resonances are still visible but at non zero energies inside the superconducting gap.