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CRP66 - Road to Higher Tc Superconductivity

Road to Higher Tc Superconductivity

LS. Uchida1, 2

1Department of Physics, University of Tokyo, Hongo, Tokyo, Japan
2AIST, Tsukuba, Japan

E-mail: uchida@lyra.phys.s.u-tokyo.ac.jp

Abstract — The highest superconducting transition temperature Tc remains 135 K (164 K at pressure of 30 GPa) which was recorded in 1993 (1994) for Hg-based trilayer cuprate. The “silence” period over 20 years is the longest in the history of superconductivity started from 1911. In contrast to the long silence in Tc, several material families have successively been found to show superconductivity at temperature higher than the old record 23 K. These include MgB2 and iron arsenides/selenides, indicating that there are several routes toward higher Tc. In fact, three different classes of high-Tc materials have recently shown a signature of higher Tc superconductivity under extreme conditions that may break the long silence.

So far the highest Tc is 55 K for bulk iron arsenides which was achieved in 2008, but Tc stopped rising since then. However, monolayer FeSe film deposited on a SrTiO3 substrate appears to show superconductivity at T = 60 K or higher [1].

MgB2 with Tc = 39 K is obviously a conventional superconductor in which phonon-mediated superconductivity is optimized. A recent report that H2S under extremely high pressures, over 150 GPa shows a superconducting signal at 190 - 203 K [2, 3], if it is real, may be understood as a case of further optimization of the circumstances in MgB2 by substitution of B with much lighter H.

Even in the case of the cuprates, it has recently been reported that the interlayer Josephson plasma mode, characteristic of the cuprate superconductivity, is transiently (for a few picoseconds) induced above 300 K by pumping c-axis polarized THz light pulses for underdoped YBCO [4].

[1] Q.Y. Wang et al., Chin. Phys. Lett. 29, 037402 (2012).
[2] A.P. Drozdov, M.I. Eremets, and I.A. Troyan, arXiv: 1412.0460.
[3] A.P. Drozdov et al., arXiv: 1506.08190.
[4] S. Kaiser et al., Phys. Rev. B 89, 184516 (2014).

Keywords (Index Terms) — Cuprates, MgB2, iron arsenides/selenides, H2S under high pressures.

IEEE/CSC & ESAS SUPERCONDUCTIVITY NEWS FORUM (global edition), April 2016. 
Submitted December 11, 2015; Selected January 23, 2016. Reference No. CRP66; Category 1,2.
Special plenary presentation SPL-2-INV given at ISS 2015 in Funabori, Tokyo, Japan, November 16 to 18th, 2015.  Not submitted to ISS 2015 Proceedings in Physica C.