專題演講

2020/09/24(Thu)     11:00 -12:00    五樓第一會議室5th Floor(1st meeting room)

Title

Proximity-Effect-Induced Superconductivity in Monatomic Ni-Pb Alloy and Ni Nanoislands

Speaker

Dr. Pin-Jui Hsu

Department of Physics, National Tsing Hua University

Abstract

Proximity effect facilitates the penetration of Cooper pairs that permits superconductivity in normal metal with reduced dimensionality, offering a promising approach to develop novel quantum phenomena and emergent phases of matters in hybrid magnetic/superconducting nanostructures. Here, we have investigated proximity-induced superconductivity in monatomic Ni-Pb alloy and Ni nanoislands grown on Pb(111) by scanning tunneling microscopy/ spectroscopy (STM/STS) combined with theoretical calculations. Through elemental Pb superconducting substrate, tunneling conductance spectra have resolved an induced superconductivity with a gap size Δ about 0.85 meV in Ni-Pb alloy, which is about 0.11 meV smaller than Pb(111). On the contrary, Ni nanoislands with honeycomb lattice display a superconductivity gap with the same size of the Pb(111) substrate. From spatially monotonic decrease of Δ across the interface between Ni-Pb alloy and Pb(111), the decay length ξL about 5 nm has been extracted. According to the Usadel fittings and the BdG model, a weak ferromagnetism with an effective temperature about 6 ~ 15 K explains such rather short decay length as well as reduced superconductivity gap in the Ni-Pb surface alloy. As for honeycomb- structured Ni nanoislands, asymmetric edge scattering of surface electrons on Pb(111) has been revealed and further theoretical insights on the details of strong suppression of backscattering at the bearded type of edges are currently in progress.