Reversible depression in theTcof thin Nb films due to enhanced hydrogen adsorption

Abstract

The effect of large hydrogen concentrations ͑Ϸ30% atomic͒, on the superconducting transition temperature T c of Nb films is discussed. The hydrogen is incorporated in solutionlike phases which occur at these concentrations because the ͑␣ to ␤͒ hydride transition in these films is suppressed. X-ray-diffraction data show an asymmetric expansion of the ͓110͔ Nb interplanar spacing. This can be as high as a 6-8 % expansion perpendicular to the plane of the film for the addition of ϳ70% hydrogen, with only a 1-2 % change in the plane of the film. T c is depressed to a value near 50% of that of the undoped film with about 30% atomic hydrogen, and returns to its initial value when the hydrogen is removed. A discussion is given of how both disorder and changes in the electronic structure can affect T c .

Hydrogen-Inclusion-Induced Critical Current Deviation of Nb/AlOx/Nb Josephson Junctions in Superconducting Integrated Circuits

“…Bulk Nb is generally known to contain hydrogen atoms and to change its characteristics [8]. For thin Nb films, Jisrawi et al reported that superconductive properties are degraded by hydrogen incorporation [5]. According to their data, the superconductive critical temperature decreases by about 0.5 to 1.0 K when Nb film includes 5 at% hydrogen.…”

First-principles calculations of niobium hydride formation in superconducting radio-frequency cavities

“…The incorporation of impurity atoms into niobium can cause a significant reduction of T c , which has been demonstrated for hydrogen dissolved interstitially in b.c.c. niobium [12]. Furthermore, several niobium hydride phases are not superconducting above 1-2 K [13][14][15].…”

Detection of surface carbon and hydrocarbons in hot spot regions of niobium superconducting rf cavities by Raman spectroscopy

“…The above-mentioned impurities are problematic for SRF cavities because they reduce the thermal conductivity of niobium, thereby reducing its ability to dissipate heat during rf operation [7]. Furthermore, dissolved oxygen [8] and hydrogen [9,10] are known to decrease the superconducting transition temperature of niobium at concentrations of a few atomic percent.…”