We performed the high hydrostatic pressure resistivity measurements (up to 1.7 GPa) on the newly discovered superconductors AxFe2Se2 (A = K and Cs) single crystals. Two batches of single crystals KxFe2Se2 with different transition temperatures (Tc) were used to study the effect of pressure. The Tc of the first one gradually decreases with increasing pressure from 32.6 K at ambient pressure. While a dome-like behavior was observed for the crystal with Tc=31.1 K, and Tc reaches its maximum value of 32.7 K at the pressure of 0.48 GPa. It indicates that there exists a optimal doping with maximum Tc of 32.7K in KxFe2Se2 system. The behavior of Tc vs. pressure for CsxFe2Se2 also shows a dome-like behavior, and Tc reaches its maximum value of 31.1 K at the pressure of 0.82 GPa. The hump observed in temperature dependence of resistivity for all the samples tends to shift to high temperature with increasing pressure. The resistivity hump could arise from the vacancy of Fe or Se.
@article{arxiv.1101.1234,
title = {Pressure effect on superconductivity of $A_{x}$Fe$_2$Se$_2$ ($A$ = K and Cs)},
author = {J. J. Ying and X. F. Wang and X. G. Luo and Z. Y. Li and Y. J. Yan and M. Zhang and A. F. Wang and P. Cheng and G. J. Ye and Z. J. Xiang and R. H. Liu and X. H. Chen},
journal= {arXiv preprint arXiv:1101.1234},
year = {2011}
}