Coexistence of Polaronic States and Superconductivity in Iron-Pnictide Compound Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O
Li-Yuan Rong1,2, Xun Shi2,3, Pierre Richard2,3,4, Yun-Lei Sun5, Guang-Han Cao5, Xiang-Zhi Zhang1, Jun-Zhang Ma2,3,6**, Ming Shi6, Yao-Bo Huang1**, Tian Qian3,4, Hong Ding2,3,4, Ren-Zhong Tai1
1Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204 2School of Physics, University of Chinese Academy of Sciences, Beijing 100190 3Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190 4Collaborative Innovation Center of Quantum Matter, Beijing 100084 5Department of Physics, Zhejiang University, Hangzhou 310027 6Paul Scherrer Institut, Swiss Light Source, Villigen PSI CH-5232, Switzerland
Abstract：The electronic structure of iron-pnictide compound superconductor Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O, which has metallic intermediate Ti$_{2}$O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show a 'peak-dip-hump' line shape with two branches of dispersion associated with the polaronic states at temperatures below around 120 K. This change in the spectra occurs along with the resistivity anomaly that was not clearly understood in a previous study. Moreover, an energy gap induced by the superconducting proximity effect opens in the polaronic bands at temperatures below $T_{\rm c}$ ($\sim$21 K). Our study provides the spectroscopic evidence that superconductivity coexists with polarons in the same bands near the Fermi level, which provides a suitable platform to study interactions between charge, lattice and spin freedoms in a correlated system.
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2018, Vol. 35 
