Abstract：

　　In most conventional superconductors, electron pairing results in translationally invariant charged superfluids with spatially uniform superfluid density. However, electron pairs can form crystalline states known as pair density waves (PDWs) that break translational symmetry from coupling with density wave orders. Experimental evidence of such exotic states remains scarce due to technical difficulties in probing the superconducting condensate with sufficient spatial resolution. I will describe our recent detection of composite PDW states induced by primary charge orders in two dichalcogenide superconductors using superconductive tips in a scanning tunneling microscope [1,2]. With the same technique, I will then discuss our ability in mapping the velocity field of electron pair fluid around quantum vortices [3] and share some perspectives on applications of such techniques in other emerging quantum materials.

　　[1] X. Liu, Y. X. Chong, R. Sharma, and J.C. Séamus Davis, Science 372, 1447-1452 (2021).

　　[2] Q Gu, J. P. Carroll, S. Wang, S. Ran, C. Broyles, H. Siddiquee, N. P. Butch, S. R. Saha, J. Paglione, J. C. Séamus Davis, and X. Liu. Nature 618, 921-927 (2023).

　　[3] X. Liu, Y. X. Chong, R. Sharma, and J.C. Séamus Davis, Nat. Mater. 20, 1480–1484 (2021).

Biosketch：

　　Xiaolong Liu received his BS degree in physics from the University of Science and Technology of China in 2013. He then pursued his PhD degree in Applied Physics at Northwestern University, where he explored the creation of entirely synthetic 2D materials such as borophene and 2D heterostructures. He joined Cornell University as a Kavli Postdoctoral Fellow in 2019, where he pioneered high-speed atomic resolution scanned Josephson tunneling microscopy. Xiaolong joined the University of Notre Dame in 2022 as an Assistant Professor of Physics. His research interest lies in the creation, visualization, and understanding of novel quantum matter and development of new quantum microscopy modalities. Experimentally, his laboratory employs cryogenic scanning probe microscopy down to 0.3 K in 9-2-2 T vector fields, single atom/molecule manipulation, and molecular beam epitaxy. Xiaolong’s research has led to over 40 peer-reviewed publications in journals including Science(3), Nature(1), Nature Materials(3), Nature Reviews Materials(1), Science Advances(3), and Nature Communications(1), which overall have attracted over 8,000 citations. Xiaolong has been the recipient of numerous awards including the Ralph E. Powe Junior Faculty Enhancement Award, IUPAP Early Career Scientist Prize in Low Temperature Physics, Nanotechnology Young Researcher Award, Nottingham Prize, and Dorothy M. and Earl S. Hoffman Award.