Magnetic and superconducting properties of vanadium nanoconstrictions

We study the magnetic and superconducting properties in a paramagnetic vanadium (V) nanoconstriction with changing its size using a mechanically controllable break junction technique. In the normal state the magnetoresistance effect is observed below the diameter d ~ 8 nm. Moreover, a Fano resonance appears around zero-bias voltage in the differential conductance for the atomic-size contacts and changes shape as the size of the constriction changes. On the other hand, below the superconducting critical temperature the superconducting gap features in V contacts are largely different from those in Pb contacts which exhibit typical features expected in superconducting point contacts. Only a single Andreev anomaly at 2Δ, where Δ is the superconducting energy gap, is observed in the spectra of the V contacts, while two anomalies at Δ and 2Δ appear in the case of the Pb contacts. In the tunnel conductance regime, the structure of the superconducting quasiparticle tunneling density of states is not seen in the V spectra in contrast to the Pb spectra. The origin of these features is discussed.