Study of niobium thin films under pressure

Abstract

Niobium is widely used in many important superconducting applications. At ambient pressure, bulk Nb has the highest critical temperature, Tc ≈ 9.25 K among the superconducting elements. Thin films of Nb show several differences in behavior in comparison with bulk Nb, e.g. substantial increase in the upper critical field (HC2). Critical temperature of superconducting transition is usually lower for thin films than in bulk sample and depends on thickness of the film, size of grains etc. We prepared 100 nm thick niobium thin films in the high vacuum DC magnetron sputtering system, with Tc = 8:95 K at ambient pressure. In this study, we performed measurements of superconducting transition temperature by electrical resistivity measurements of Nb thin film under hydrostatic pressure of up to 30 kbar. We observed an increase of Tc with increasing value of pressure (dT c/dp = 7:3 mK/kbar). On the other side in the case of bulk sample of Nb we observed a decrease of Tc value (dTc/dp = -2.5 mK/kbar) with increasing applied pressure. Difference in superconducting properties between niobium bulk and thin film under pressure is discussed.