Coherent excitations and electron phonon coupling in Ba/EuFe_2As_2 compounds investigated by femtosecond time- and angle-resolved photoemission spectroscopy
Isabella Avigo, Rocio Cortés, Laurenz Rettig, Setti Thirupathaiah, Hirale S. Jeevan, Philipp Gegenwart, Thomas Wolf, Manuel Ligges, Martin Wolf, Jörg Fink, Uwe Bovensiepen
We employed femtosecond time- and angle-resolved photoelectron spectroscopy to analyze the response of the electronic structure of the 122 Fe-pnictide parent compounds Ba/EuFe_2As_2 and optimally doped BaFe_{1.85}Co_{0.15}As_2 near the Γpoint to femtosecond optical excitation. We identify pronounced changes of the electron population within several 100 meV above and below the Fermi level, which we explain as combination of (i) coherent lattice vibrations, (ii) a hot electron and hole distribution, and (iii) transient modifications of the chemical potential. The response of the three different materials is very similar. In the Fourier transformation of the time-dependent photoemission intensity we identify three modes at 5.6, 3.3, and 2.6 THz. While the highest frequency mode is safely assigned to the A_{1g} mode, the other two modes require a discussion in comparison to literature. The time-dependent evolution of the hot electron distribution follows a simplified description of a transient three temperature model which considers two heat baths of lattice vibrations, which are more weakly and strongly coupled to transiently excited electron population. Still the energy transfer from electrons to the strongly coupled phonons results in a rather weak, momentum-averaged electron-phonon coupling quantified by values for λ<ω^2> between 30 and 70 meV^2. The chemical potential is found to present a transient modulation induced by the coherent phonons. This change in the chemical potential is particularly strong in a two band system like in the 122 Fe-pnictide compounds investigated here due to the pronounced variation of the electrons density of states close to the equilibrium chemical potential.
Development of a 10.8-eV Tabletop Femtosecond Laser with Tunable Polarization for High-Resolution Angle-Resolved Photoemission Spectroscopy
Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University（清华大学物理系低维量子物理国家重点实验室）；School of Information Science and Engineering, Shandong University（山东大学信息科学与工程学院）；Tsientang Institute for Advanced Study, Zhejiang（浙江千唐高等研究院）；Interdisciplinary Institute of Light-Element Quantum Materials and Research Center for Light- Element Advanced Materials, Peking University（北京大学轻元素量子材料交叉研究院及轻元素先进材料研究中心）；Songshan Lake Materials Laboratory（松山湖材料实验室）
Time-Resolved Photoemission Spectroscopy of Quantum Materials Using High Harmonic Generation: Probing Electron-Phonon Interactions and Non-Equilibrium Dynamics
Institute for Solid State Physics, The University of Tokyo（东京大学固体物理研究所）；Trans-scale Quantum Science Institute, The University of Tokyo（东京大学跨尺度量子科学研究所）；Material Innovation Research Center, The University of Tokyo（东京大学材料创新中心）
Ultrafast electron dynamics in Au/Fe/MgO(001) analyzed by Au- and Fe-selective pumping in time-resolved two-photon photoemission spectroscopy: Separation of excitations in adjacent metallic layers
Ultrafast transport and energy relaxation of hot electrons in Au/Fe/MgO(001) heterostructures analyzed by linear time-resolved photoelectron spectroscopy
Ultrafast Optical Excitation of a Persistent Surface-State Population in the Topological Insulator Bi2Se3
利用飞秒时间和角度分辨光电子能谱研究了拓扑绝缘体Bi 2 Se 3的非平衡动力学行为。我们研究了p型Bi_2Se_3，其中金属狄拉克表面态和体导带未被占据。光学激发导致在体导带边缘处的亚稳态布居，其供给表面态的非平衡布居，该非平衡布居持续>10ps。这种具有自旋纹理的金属狄拉克表面态的异常长寿的人口可能会提供一个驱动瞬态自旋极化电流的通道。
Observing the spatial and temporal evolution of exciton wave functions
Philipps-Universität Marburg（马尔堡菲利普斯大学）；University of Regensburg（雷根斯堡大学）；University of Graz（格拉茨大学）；Forschungszentrum Jülich（于利希研究中心）；RWTH Aachen University（亚琛工业大学）
