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Intrigued by the discovery of high-temperature superconductivity in a single unit-cell layer of FeSe film on SrTiO3, researchers recently found large superconductinglike energy gaps in K-adsorbed multilayer FeSe films by angle-resolved photoemission and scanning tunneling spectroscopy. However, the existence and nature of the high-temperature superconductivity inferred by the spectroscopic studies has not been investigated by measurements of zero resistance or the Meissner effect due to the fragility of K atoms in air. Using a self-developed multifunctional scanning tunneling microscope, we succeed in observing the diamagnetic response of K-adsorbed multilayer FeSe films, and thus find a dome-shaped relation between the critical temperature (Tc) and K coverage. Intriguingly, Tc exhibits an approximately linear dependence on the superfluid density in the whole K adsorbed region. Moreover, the quadratic low-temperature variation in the London penetration depth indicates a sign-reversal order parameter. Furthermore, the critical magnetic field H(T) reveals an upward divergence with decreasing temperature, in line with vortex melting. These results provide compelling information towards further understanding of the high-temperature superconductivity in FeSe-derived superconductors.
References
[1] Diamagnetic Response of Potassium-Adsorbed Multilayer FeSe Film. Gang Yao, Ming-Chao Duan, Ningning Liu, et al. Physical Review Letters, 123, 257001 (2019).
[2] Vortex-Melting Origin for the Upward Curvature of the Pseudo-Upper-Critical Field in Potassium Adsorbed Multilayer FeSe Film. Gang Yao, Yueqiao Qu, Ningning Liu, et al. (to be submitted).
2015.4-2020.6 Shanghai Jiao Tong University, Ph.D
2012.4-2014.6 China Academy of Engineering Physics, Joint M.S.
2011.9-2014.6 Southwest University of Science and Technology, M.S.
2007.9-2011.6 Leshan Normal University, B.S.
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