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.
@article{arxiv.1301.2748,
title = {Interface-induced superconductivity and strain-dependent spin density wave in FeSe/SrTiO3 thin films},
author = {S. Y. Tan and M. Xia and Y. Zhang and Z. R. Ye and F. Chen and X. Xie and R. Peng and D. F. Xu and Q. Fan and H. C. Xu and J. Juan and T. Zhang and X. C. Lai and T. Xiang and J. P. Hu and B. P. Xie and D. L. Feng},
journal= {arXiv preprint arXiv:1301.2748},
year = {2015}
}