Resistivity Measurements in Palladium Hydride Film Prepared by Low-Temperature Hydrogen Absorption Method

We investigated the superconducting properties of a palladium hydride (PdH_x; x = H/Pd) film with a thickness of ∼100 nm prepared by a low-temperature hydrogen (H) absorption method. H atoms were loaded to a Pd film in H₂ gas pressure of ∼0.25 MPa at temperatures of T = 180 and 150 K. At T = 180 K, after the resistivity variation due to H absorption was almost stopped, the PdH_x film was cooled rapidly to low temperatures for the resistivity measurements. A superconducting transition was observed at T_c ∼ 1.1 K, where the transition width is smaller than 0.1 K. This indicates that a high-quality sample with a sharp transition can be obtained by providing sufficient time for H absorption. At T = 150 K, although the resistivity variation remained, the film was cooled. The transition temperature T_c increased to ∼2.1 K, whereas the transition width increased owing to the inhomogeneity of the H concentration in the film. Curiously, regardless of the H homogeneity, there remained a similar T-dependent residual resistivity in both films prepared at T = 180 and 150 K after the superconducting transition. This implies that the observed residual resistivity is essential for the future of the system, although its origin is not clear.