D. Tristan Jover

INTRINSIC AND CARRIER DENSITY EFFECTS ON THE PRESSURE DEPENDENCE OF TC OF HIGH-TEMPERATURE SUPERCONDUCTORS

The pressure dependence of „ # in high-temperature superconductors is experimentally found to be influenced not only by a pressure-induced increase in charge carrier density but also by intrisic e⁄ects. The influence of both contributions was systematically investigated in Tl 0.5 Pb 0.5 Sr 2 Ca 1~x Y x Cu 2 O 7 . The behavior of superconductors with three or four CuO 2 -layers is further complicated by the inequivalence of the inner and outer CuO 2 -layers. High-pressure experiments up to 46 GPa are analyzed in view of the above. ( 1999 Elsevier Science B.V. All rights reserved.

Superconductivity at 133 K in Tl2Ba2Ca2Cu3O10+x under high pressure

Abstract The pressure dependence of the superconducting transition temperature T c of Tl 2 Ba 2 Ca 2 Cu 3 O 10+ x (Tl-2223) has been measu red under pressures up to 13 GPa (130 kbar). At 4.2 GPa a maximum is observed with a T c of 133 K. This is the highest T c yet observed for any high- T c superconductor with the exception of the recently discovered mercury-based compound HgBa 2 Ca 2 Cu 3 O 8+ x (Hg-1223). Because of some structural differences between Tl-2223 and Hg-1223, a slightly higher maximum T c is predicted for Hg-1223. Both T c and its pressure dependence are discussed on the basis of a simple charge-transfer model.

Pressure dependence of the superconducting critical temperature Tc of HgBa2Ca2Cu3O8+x up to 26 GPa

Abstract The pressure dependence of the newly discovered mercury-compound HgBa 2 Ca 2 Cu 3 O 8+ x (Hg-1223) has been studied in detail up to 26 GPa in a cryogenic diamond anvil cell on a sample with a single superconducting phase. Although initially T c increases from 135 K at a rate of 1.0 K/GPa, at intermediate pressures ∂T c / ∂ p decreases rapidly. When pressure is increased further, however, T c rises again significantly up to 145 K at 26 GPa (where ∂T c / ∂ p ≅ 0.4 K/GPa). These results can be understood qualitatively on the basis of a charge-transfer model which allows a non-homogeneous distribution of holes among the inequivalent CuO 2 layers.

Ultra high pressure experiments on high-Tc superconductors

In this review we treat various selected properties of superconductors under ultra high pressure. Emphasis is given to the superconducting parameters Tc and Hc2 in high temperature superconductors. The pressure dependence of Tc is explained using a phenomenological model.