Road to Higher T_c Superconductivity

LS. Uchida^{1, 2}

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

E-mail: [email protected]

Abstract — The highest superconducting transition temperature T_c 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 T_c, 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 T_c. In fact, three different classes of high-T_c materials have recently shown a signature of higher T_c superconductivity under extreme conditions that may break the long silence.

So far the highest T_c is 55 K for bulk iron arsenides which was achieved in 2008, but T_c 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 T_c = 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.