Hydrostatic pressure effect on the transport properties in TiO superconducting thin films

Abstract

The superconducting properties of the TiO epitaxial thin films were systematically investigated under hydrostatic pressures $(P)$ up to 2.13 GPa. At ambient pressure, the normal state resistivity increases with decreasing temperature, and steeply increases below ${T}_{\mathrm{kink}}\ensuremath{\sim}115\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. With further reducing temperature to ${T}_{c}\ensuremath{\sim}5.99\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the thin film enters into a superconducting state. Interestingly, the superconducting temperature ${T}_{c}$ gradually decreases upon increasing $P$, and the decreasing rate of ${T}_{c}$ with $P$ is much larger than the McMillan theoretical expectation. In contrast, ${T}_{\mathrm{kink}}$ increases with $P$ and a remarkable resistivity enhancement was observed in the temperature range between ${T}_{\mathrm{kink}}$ and ${T}_{c}$. The variations of ${T}_{c},{T}_{\mathrm{kink}}$, and normal state resistivity under high pressure may be induced by the charge localization related to the atomic vacancies rearrangement in TiO thin film. Furthermore, the temperature dependencies of the upper critical field ${H}_{c2}(T)$ indicate that both the orbital and Pauli-paramagnetic pair-breaking effects should be taken into account. Finally, the thermally activated flux flow investigations under different pressures suggest that the pressure will suppress the thermal activate energy.