title: Ultrafast Dynamics Evidence of High Temperature Superconductivity in Single Unit Cell FeSe on SrTiO_{3}.
abstract: We report the time-resolved excited state ultrafast dynamics of single unit cell (1 UC) thick FeSe films on SrTiO_{3} (STO), with FeTe capping layers. By measuring the photoexcited quasiparticles' density and lifetime, we unambiguously identify a superconducting (SC) phase transition, with a transition temperature T_{c} of 68 (-5/+2)  K and a SC gap of Δ(0)=20.2±1.5  meV. The obtained electron-phonon coupling strength λ is as large as 0.48, demonstrating the likely crucial role of electron-phonon coupling in the high temperature superconductivity of the 1 UC FeSe on STO systems. We further find a 0.05 THz coherent acoustic phonon branch in the capping layer, which provides an additional decay channel to the gluing bosons.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Y C
authors.initials: YC
authors.lastname: Tian
authors.affiliation: State Key Laboratory for Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.
authors.forename: W H
authors.initials: WH
authors.lastname: Zhang
authors.affiliation: State Key Laboratory for Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.
authors.forename: F S
authors.initials: FS
authors.lastname: Li
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Y L
authors.initials: YL
authors.lastname: Wu
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Q
authors.initials: Q
authors.lastname: Wu
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: F
authors.initials: F
authors.lastname: Sun
authors.affiliation: State Key Laboratory for Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.
authors.forename: G Y
authors.initials: GY
authors.lastname: Zhou
authors.affiliation: State Key Laboratory for Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.|Collaborative Innovation Center of Quantum Matter, Beijing 100084, China.
authors.forename: Lili
authors.initials: L
authors.lastname: Wang
authors.affiliation: State Key Laboratory for Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.|Collaborative Innovation Center of Quantum Matter, Beijing 100084, China.
authors.forename: Xucun
authors.initials: X
authors.lastname: Ma
authors.affiliation: State Key Laboratory for Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.|Collaborative Innovation Center of Quantum Matter, Beijing 100084, China.
authors.forename: Qi-Kun
authors.initials: QK
authors.lastname: Xue
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Jimin
authors.initials: J
authors.lastname: Zhao