Synthesis of Thin Niobium Films on Silicon and Study of Their Superconducting Properties in the Dimensional Crossover Region

Abstract

Niobium films with a thickness of 4–100 nm are synthesized on a silicon substrate under ultrahigh vacuum conditions. Measurements of the electrical resistance show a high superconducting transition temperature Tc in the range of 4.7–9.1 K and record-breaking small transition widths ΔTc in the range of 260–11 m. The dependences of Tc and ΔTc on the magnetic field are investigated, and the superconducting coherence lengths and mean free paths of conduction electrons for different thicknesses of the synthesized films are determined. A significant influence of the magnetic field on ΔTc is found, which reveals the transition from three- to two-dimensional superconductivity at thicknesses below 10 nm. The dependences of Tc and ΔTc on the thickness of the films and the magnitude of the magnetic field are discussed within the framework of existing theories of superconductivity in thin films of superconducting metals.