Pressure dependence of the superconducting critical temperature of Tl2Ba2Ca2Cu3O10+y and Tl2Ba2Ca3Cu4O12+y up to 21 GPa

Extremely Overdoped Superconducting Cuprates via High Pressure Oxygenation Methods

Within the cuprate constellation, one fixed star has been the superconducting dome in the quantum phase diagram of transition temperature vs. the excess charge on the Cu in the CuO2-planes, p, resulting from O-doping or cation substitution. However, a more extensive search of the literature shows that the loss of the superconductivity in favor of a normal Fermi liquid on the overdoped side should not be assumed. Many experimental results from cuprates prepared by high-pressure oxygenation show Tc converging to a fixed value or continuing to slowly increase past the upper limit of the dome of p = 0.26–0.27, up to the maximum amounts of excess oxygen corresponding to p values of 0.3 to > 0.6. These reports have been met with disinterest or disregard. Our review shows that dome-breaking trends for Tc are, in fact, the result of careful, accurate experimental work on a large number of compounds. This behavior most likely mandates a revision of the theoretical basis for high-temperature superconductivity. That excess O atoms located in specific, metastable sites in the crystal, attainable only with extreme O chemical activity under HPO conditions, cause such a radical extension of the superconductivity points to a much more substantial role for the lattice in terms of internal chemistry and bonding.

Effect of Pressure on the Superconducting Properties of Tl2Ba2Ca2Cu3O9-δ

This study investigated the application of pressure on the superconducting properties of a thallium-based cuprate, namely Tl2Ba2Ca2Cu3O9-δ (Tl-2223). The superconducting transition temperature (Tc) and the critical current density (Jc) were studied by applying ~1 GPa of pressure. This hydrostatic pressure was applied in a piston-cylinder-cell (PCC), using Pb as a manometer and Daphne 7373 oil as the pressure transmitting medium. For estimating the Jc, we used Bean’s critical state formula on the magnetic hysteresis curves at 10 K and 20 K. Both the Tc and Jc improved with pressure. The Jc values increased at both temperatures and the Tc value increased by 4 K with a pressure of 0.8 GPa. These results clearly indicate that pressure is another tool to control properties of quantum materials.