Host: Prof. Baiqing Lv

Abstract:

Surface complexity and disorder of 122-type ferro-pnictide superconductors have long hindered surface-sensitive probes from revealing their intrinsic properties and unusual quantum states. In this talk, I will present our recent experimental advances in the atomic-scale preparation and characterization of surface-engineered, high-quality A(Fe1-xCox)2As2 (A = alkaline earth metals) epitaxial films, achieved through a combination of molecular beam epitaxy, scanning tunnelling microscopy, and macroscopic transport measurements. By precisely controlling surface terminations, we have successfully obtained distinct terminations in multiple ferro-pnictide films, enabling us to directly visualize atomic-scale electronic nematicity and its evolution with electron doping on the FeAs-terminated surface, as well as to reveal intrinsic, nodeless superconducting gaps via BaAs/FeAs heterostructure engineering. Moreover, spectroscopic measurements within magnetic vortex cores reveal previously unidentified bound states pointing toward topological features and charge-stripe order. Along with topological transport signatures in modulated ferro-pnictide films, our findings establish a versatile platform for exploring the interplay among electronic nematicity, unconventional superconductivity, charge order, and nontrivial topology in ferropnictides.

Biography:

Can-Li Song obtained his PhD degree in Physics from Tsinghua University in 2011. From 2011 to 2014, He was a Lawrence Golub Postdoctoral Fellow in the Department of Physics at Harvard University. He then returned to the Department of Physics at Tsinghua University, where he has been a tenured associate professor since 2021. His research focuses on molecular beam epitaxy growth and scanning tunneling microscopy studies of unconventional high-temperature superconductors and topological quantum materials.