Enhancement of superconducting transition temperature in Nb/Pd bilayers upon rapid thermal hydrogenation

Abstract

Recent discoveries of high-Tc superconducting hydrides at high pressure have opened up new possibilities for improving the superconducting transition temperature (Tc) using hydrogenation. Here, a unique thermodynamic approach is developed based on the concept of rapid thermal annealing and is adopted to study the hydrogenation effect on the superconducting properties of Nb/Pd bilayer films. Below 300∘C annealing temperatures, the Tc is enhanced from 8.77 to 9.06 K and is correlated with the compression of the Nb unit cell. A weak lattice expansion occurs at higher annealing temperatures, and the Tc is gradually suppressed. Furthermore, the rapid thermal hydrogenation affects the Tc differently depending on the substrate on which the Nb/Pd bilayers are grown. For the c-cut Al2O3 substrate, the Tc reduction starts at 250∘C, while for the r-cut Al2O3, this occurs at 350∘C. We associate these features with the elastic behavior of Nb film upon hydrogenation. A proposed model shows that the increase of Tc could be caused by the compressive stress related to the rapid nucleation of hydrides or the removal of impurities. Our discoveries provide insights into how superconductivity can be manipulated by rapid thermal hydrogenation.

Source-reported materials — not catalogue approval

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