Abstract
Since the early days of Bardeen-Cooper-Schrieffer theory, it has been predicted that a sufficiently large supercurrent can close the energy gap in a superconductor and create gapless Bogoliubov quasiparticles through the Doppler shift of quasiparticle energy due to the Cooper pair momentum[1]. In this gapless superconducting state, zero-energy quasiparticles reside on a segment of the normal state Fermi surface, while its remaining part is still gapped. However, the segmented Fermi surface of a finite-momentum state carrying a supercurrent has never been detected directly. Here we use quasiparticle interference (QPI) technique to image field-controlled Fermi surface of Bi2Te3 thin films proximitized by the superconductor NbSe2. By applying a small in-plane magnetic field, a screening supercurrent is induced which leads to finite-momentum pairing on topological surface states of Bi2Te3[2]. Our measurements and analysis reveal the strong impact of finite Cooper pair momentum on the quasiparticle spectrum, and thus pave the way for STM study of pair density wave and FFLO states in unconventional superconductors.
[1] Phys. Rev. 137, A783-A787 (1965)
[2] Science 374, 1381-1385(2021)
Biography
Prof. ZHENG obtained his Ph.D degree from institute of Physics, Chinese Academy of Science in 2007. After postdoctoral research at Birmingham University UK, Kiel University Germany and Princeton University USA, he joined Shanghai Jiao Tong University in 2017 as a tenure-tracked associate professor and was promoted to professor in 2020. His research interests include experimental study of topological matters, low dimensional materials, unconventional superconductors and novel quasiparticles in many-body systems. He has published more than 90 papers, including 3 in Science and 15 in PRL.
Anyone interested is welcome to attend.