Effect of external electromagnetic radiation on the anomalous metallic behavior in superconducting Ta thin films

Abstract

©2020 American Physical Society. We investigated the transport characteristics of superconducting Ta thin films with three configurations of radio-frequency radiation filters: no filter, only room-temperature filter, and low- and room-temperature filters. We find that when the room-temperature filter is installed, the entire transition is shifted to higher temperatures, and once the zero-resistance state is achieved at zero magnetic field, no strong radiation effect is observed. When the magnetic field is turned on, the non-zero-resistance saturation at low temperatures is revealed without low-temperature filters, which has previously been considered to be a magnetic-field-induced quantum metallic phase. However, the insertion of the additional low-temperature filters weakens the saturation of the resistance, i.e., the signature of the metallic behavior. This observation suggests that the previously reported anomalous metallic state in Ta films is mainly induced by unfiltered radiation, and, thus, the intrinsic metallic ground state, if it exists, should be limited to a narrow range of magnetic fields near the critical point