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TT: Fachverband Tiefe Temperaturen

TT 55: Topology and Symmetry Protected Materials (joint session O/TT)

TT 55.3: Talk

Wednesday, March 20, 2024, 15:30–15:45, HL 001

Discovery of Segmented Fermi Surface — •Hao Zheng — Shanghai Jiao Tong University, Shanghai, China

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. 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)

Keywords: Molecular Beam Epitaxy; Scanning Tunneling Microscopy; topological surface state; superconductor; Cooper pair momentum