Regensburg 2022 – scientific programme
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O: Fachverband Oberflächenphysik
O 18: Poster Monday: 2D Materials 1
O 18.15: Poster
Monday, September 5, 2022, 18:00–20:00, P4
Spectroscopic evidence of BCS-BEC crossover in FeSe monolayer — •wantong huang1,6, haicheng lin1, gautam rai2, yuguo yin1, lianyi he1, qi-kun xue1,5, stephan wolfgang haas2,3, stefan kettemann3,4, xi chen1,5, and shuai-hua ji1,5 — 1State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China — 2Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089-0484, USA — 3Jacobs University, Campus Ring 1, 28759 Bremen, Germany — 4Division of Advanced Materials Science,POSTECH, San 31, Hyoja-dong, Nam-gu, Pohang 790-784, South Korea — 5Frontier Science Center for Quantum Information, Beijing 100084, China — 6Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
It has been difficult to realize the crossover from Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensates (BEC) in solids. Here we report direct evidence of BEC in a FeSe monolayer. The Fermi energy of the FeSe film can be tuned by graphene/SiC substrate to realize a BCS-BEC crossover. As the Fermi energy drops, the local density of states measured by STM evolves continuously from a BCS gap to a step-like asymmetric spectrum of BEC state. The theoretical calculation based on a two-band model reproduces well the measured spectra and, in particular, identifies features in the quasi-particle density of states that indicate a transition from the BCS to the BEC regime. In addition, the Zeeman splitting of the quasi-particle states is found to be consistent with the characteristics of a condensate.