Interface enhanced superconductivity in one unit-cell FeSe films grown on SrTiO3

Heterostructure based interface engineering has been proved an effective method for finding new superconducting systems and raising superconducting transition temperature (Tc). Recently discovered high temperature superconductivity in one unit-cell (UC) FeSe films on SrTiO3 (STO) substrate grown by molecular beam epitaxy has attracted intensive attention. In sharp contrast to FeSe films on graphene where a 2.2 meV superconducting gap is observed on thick films and no superconducting gap on 1-UC FeSe down to 2.3 K, 1-UC FeSe films on STO substrate exhibit unexpected large superconducting gaps of 15-20 meV. Interestingly, the anomalously large superconducting gap is only found in the first UC FeSe but not on 2-UC or thicker layers, indicating that interface plays a crucial role in the enhanced superconductivity in 1-UC FeSe films on STO substrate. Another interesting point of this system is its simple band structure that consists only of electron Fermi pockets at M points, which is different from that of bulk FeSe. In this talk, a comprehensive study of 1-UC FeSe films by in situ scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoemission spectroscopy (ARPES) and ex situ transport measurements will be presented to discuss the possible superconducting mechanism in this well-defined heterostructure. \\[4pt] Collaborators: Qi-Kun Xue, Lili Wang, Yayu Wang (Tsinghua University); Xingjiang Zhou (Institute of Physics, CAS); Jian Wang (Peking University)