Figure 1. The (NH3)yCs0.4FeSe sample prepared by liquid ammonia technique.
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Figure 2: Phase diagram of (NH3)yCs0.4FeSe.
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Research Highlights

High-Tc superconductivity found under high pressure

Drastic enhancement of superconducting transition temperature (Tc) can be induced by placing materials under high pressure, state Yoshihiro Kubozono and his team at Okayama University.

In previous studies, Metal-intercalated FeSe’s prepared using liquid ammonia technique showed very high Tc of 30 - 45 K. With an increase in FeSe plane spacing (d), the Tc increased rapidly, showing that the increase in two-dimensionality leads to the higher Tc.

Until recently, the limit of Tc was recognized as 45 K, because of a saturation of Tc – d plot1. Sun et al. conducted a study during which, in the pressure-induced high-Tc superconducting phase for two metal doped FeSe materials (Tl0.6Rb0.4Fe1.67Se2 and K0.8Fe1.7Se2), the maximum Tc reached 48 K2. However, such behavior has rarely been reported because it is extremely difficult to conduct the necessary experiments.

In a recent study, Kubozono and his team applied high-pressure to ammoniated Cs doped FeSe ((NH3)yCs0.4FeSe)) material. They measured the temperature dependence of resistance under pressures of between 0 – 41 GPa.

The Tc of (NH3)yCs0.4FeSe (31 K at ambient pressure) gradually decreased with increasing pressure, and no superconductivity was observed down to 4.2 K at 11 - 13 GPa. The superconductivity reemerged rapidly above 13 GPa, and a dome-like pressure-dependence of Tc was found at 15 - 41 GPa. The maximum Tc reached 49 K at 21 GPa.

The emergence of high-Tc phase under high pressure may be characteristic for all metal doped FeSe materials, which may provide a hint for realizing higher Tc superconductors in two-dimensional layered materials in future.

1 S. Hosono et al. J. Phys. Soc. Jpn. 83, 113704 (2014).

2 L. Sun et al. Nature 483, 67 (2012).

・Authors: M. Izumi, L. Zheng, Y. Sakai, H. Goto, M. Sakata, Y. Nakamoto, H. L. T. Nguyen, T. Kagayama, K. Shimizu, S. Araki, T. C. Kobayashi, T. Kambe, D. Gu, J. Guo, J. Liu, Y. Li, L. Sun, K. Prassides, Y. Kubozono
・Title of original paper: Emergence of double-dome superconductivity in ammoniated metal-doped FeSe
・Journal, volume, pages and year: Scientific Reports 5, 9477 (2015).
・Digital Object Identifier (DOI): 10.1038/srep09477
・Affiliations: Research Laboratory for Surface Science, Okayama University and six Research groups
・Department website: http://interfa.rlss.okayama-u.ac.jp/index.html