Ultrafast Dynamics in Phase-Separated (Na0.32K0.68)0.95Fe1.75Se2 Superconductors by Using Dual-Color Pump Probe Spectroscopy
P. C. Cheng1*, C. W. Luo1,2, Y. J. Chu1, W. Y. Tzeng1, J.-Y. Lin3, K. H. Wu1, J. Y. Juang1, T. Kobayashi1,4, Alexey Golovanov5, D. A. Chareev6,7, Alexander Vasiliev5,6,8
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2Taiwan Consortium of Emergent Crystalline Materials, Ministry of Science and Technology, Taipei, Taiwan
3Institute of Physics, National Chiao Tung University, Hsinchu, Taiwan
4Department of Applied Physics and Chemistry and Institute for Laser Science, University of Electro-Communications, Tokyo, Japan
5Physics Faculty, Moscow State University, Moscow, Russian Federation
6Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russian Federation
7Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Russian Federation
8National University of Science and Technology, MISiS, Moscow, Russian Federation
* presenting author:Po Chung Cheng, email:pccheng1115@gmail.com
We present the temperature-dependent ultrafast pump-probe spectra in phase-separated (Na0.32K0.68)0.95Fe1.75Se2 single crystals from 20 to 290 K. After pumping with photon energy of 3.1 eV, the time evolution of transient reflectivity changes (ΔR/R) in picosecond timescale is detected by 1.55-eV femtosecond pulses. The amplitude of ΔR/R rises dramatically at superconducting critical temperature Tc (=30 K) due to the opening of a superconducting gap (~10.8 meV). In addition, the orbital selective Mott phase (OSMP) transition has been observed at 100 K (T*), which indicates that the electron correlation plays an important role in alkaline iron selenide superconductors. The metallic phase and antiferromagnetic insulating phase are correlated by the interaction between electrons, which persists below Tc. These results not only imply the coexistence of superconducting phase and antiferromagnetic phase at Tc but also provide a new aspect to clarify the pairing mechanism in alkali metal iron selenide superconductors.

Keywords: iron base superconductor, ultrafast dynamics