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Stanford University
APPLIED PHYSICS/PHYSICS COLLOQUIUM

Tuesday, February 19, 2019
4:30 p.m. on campus in Hewlett Teaching Center, Rm. 201
Refreshments in the Physics Lobby at 4:15 p.m.

Shin-ichi Uchida
University of Tokyo

“The Road to Higher Tc Superconductivity”

Unravelling the mechanism of high-Tc superconductivity is one of the most challenging problems in physics. Equally challenging is to enhance the superconducting transition temperature Tc, but Tc at ambient conditions has stopped rising for almost 25 years since 135 K was recorded for the Hg-based trilayer cuprate in 1993. However, in recent years, three different classes of high-Tc materials have shown a signature of higher Tc under extreme conditions; monolayer FeSe films deposited on a SrTiO3 substrate, H3S (and LaHx) under extremely high pressures, and YBCO pumped by c-axis polarized THz light pulses. These indicate that there is a room for the Tc–enhancement in the known high-Tc classes, specifically, the cuprate and the iron-based superconducting materials.

The first part of this colloquium addresses the question of why copper oxides and iron arsenides/selenides are special, and then a possibility of finding the third high-Tc materials containing 3d transition-metal elements will be suggested. The second part focusses on the hole-doped high-Tc cuprates, and an attempt to search for a new type of cuprate materials with structures more favorable for higher Tc. A candidate new cuprate is Ba2CuO4-y (and its Sr counterpart Sr2CuO4-y with Tc = 98 K) in which high-Tc superconductivity occurs in highly oxygen-deficient Cu-O planes with high hole density and short apical oxygen distance. A possible structure of this new cuprate will be discussed.