S. Y. Tan, M. Xia, Y. Zhang, Z. R. Ye, F. Chen, X. Xie, R. Peng, D. F. Xu, Q. Fan, H. C. Xu, J. Juan, T. Zhang, X. C. Lai, T. Xiang, J. P. Hu, B. P. Xie, D. L. Feng
The record of superconducting transition temperature(Tc) has long been 56K for the iron-based high temperature superconductors(Fe-HTS's). Recently, in single layer FeSe films grown on SrTiO3 substrate, signs for a new 65K Tc record are reported. Here with in-situ photoemission measurements, we substantiate the presence of the spin density wave(SDW) in FeSe films, a key ingredient of Fe-HTS that was missed in FeSe before, which weakens with increased thickness or reduced strain. We demonstrate that the superconductivity occurs when the electrons transferred from the oxygen-vacant substrate suppress the otherwise most pronounced SDW in single layer FeSe. Besides providing a comprehensive understanding of FeSe films and directions to further enhance its Tc, we establish the phase diagram of FeSe vs. lattice constant that contains all the essential physics of Fe-HTS's. With the simplest structure, cleanest composition and single tuning parameter, it is ideal for testing theories of Fe-HTS's.
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http://arxiv.org/abs/1301.2748
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