E. N. Van Eenige

Superconductivity at 108 K in YBa2Cu4O8 at pressures up to 12 GPa

Abstract Resistive measurements in a cryogenic diamond anvil cell show that the T c of YBa 2 Cu 4 O 8 can be increased by almost 30 K by applying a pressure of 12 GPa. The pressure derivative is, however, not constant. At p ⪷ 5 GPa, d T c /d p ≊ 5 K/GPa. At higher pressures d T c /d p decreases gradually and T c saturates at ≈ 108 K. This behaviour is reproduced by a phenomenological model where T c depends only on the number of holes in the CuO 2 planes.

Pressure dependence of the Tc of BiCaSrCuO up to 80 kbar

Abstract The superconducting transition temperature T c of polycrystalline BiCaSrCuO ( T c =92.4 K) was measured by monitoring the electrical resistivity in a diamond anvil cell. T c is found to decrease at a rate of d T c /d p =−0.16 K/kbar up to 80 kbar. This is the first high temperature superconductor which shows a clear decrease of T c with pressure. The pressure dependence is qualitatively explained in terms of a Hubbard-like model.

High pressure changes the charge carrier concentration in high-Tc superconductors: Experiments to 50 GPa

Abstract For the first time the T c of high temperature superconductors was measured up to 50 GPa, corresponding to a volume compression of −25%. The T c of YBa 2 Cu 4 O 8 was found to increase from 78 K to a maximum of 106 K at −10 GPa before decreasing again, while the T c of CaLaBaCu 3 O 7 only changed from 80 K to 86 K at −35 GPa. The charge carrier concentration δ(p) is calculated from our simultaneous measurement of the upper critical field H c2 (p) and T c (p). An excellent description of the pressure dependence of T c is given by a simple model. Also the enigmatic pressure dependence of the La 2−x Sr x CuO 4 compounds, as measured by Tanahashi et al. can be understood within the same framework.

High temperature superconductors under pressure: Experimental review and test on the RVB model

Abstract An update is given of all published data on δTc/δp, extending our previous review. Implications of new data for the RVB model are discussed. Under particular assumptions a striking discrepancy is found.

Pressure dependence of Tc and Hc2 of CaLaBaCu3O7 up to 50 GPa

Abstract At ϖln T c ϖp =1.5×10 -3 GPa -1 , the relative change of the superconducting critical temperature T c with pressure p in CaLaBaCu 3 O 7 is found to be smaller than in any other high- T c compound. Even more remarkable is that this low value applies to the whole range from 0 to 50 GPa (with is the highest pressure ever reached in the investigation of T c for any compound). Using measurements of the upper critical field H c2 ( T, p ) to 40 GPa, we deduce that (1) the charge carrier concentration is virtually unaffected by pressure, in striking contrast with e.g. YBa 2 Cu 4 O 8 and (2) that the net effect on T c of the pressure induced changes of all other parameters is extremely small.

Electrical properties and Tc of Bi2CaSr2Cu2O8 up to pressures of 15 GPA

Abstract By means of four-point resistivity measurements the critical temperature of Bi 2 CaSr 2 Cu 2 O 8 was studied under high pressure. Evidence for three phases, one non-superconducting and two superconducting with T c s of 80 and 110 K is found. Both T c s are only weakly pressure dependent. The non-superconducting background increases with pressure and with measurement current indicating the presence of weak links and a “weakening” of these links with pressure.

High-Tc Superconductors Under Very High Pressure

High pressure has played a crucial role in the short history of high Tc superconductors. Soon after the discovery of superconductivity by Bednorz and Muller1 in La-Ba-Cu-O, Chu et al.2 showed that the critical temperature Tc could be significantly increased by pressure. This observation led to the discovery of YBa2Cu3O7 by Wu et al.3 with a Tc above 90 K. Incidentally, this high Tc is probably also due to the fact that YBa2Cu3O7 has two CuO2 layers per unit cell instead of a single one in La-Ba-Cu-O.

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.

Conventional and high T-c superconductors under high pressure

Abstract By means of a cryogenic diamond anvil cell the pressure dependence of the superconducting Tc of i) palladium hydrides and deuterides and ii) various high-Tc superconductors (YBa2Cu3O7, CaLaBaCu3O7 and Bi2CaSr2Cu2O8) has been determined. The results agree with the general trend of dln Tc/dp versus Tc observed previously. A possible explanation of this trend is given and exceptions discussed.

Electrical properties and Tc of CaLaBaCu3Ox at pressures up to 9 GPa

Abstract By means of a four-point resistivity method the critical temperature (Tc) of the tetragonal high temperature super-conductor CaLaBaCu3Ox was studied for pressures up to 9 GPa. The pressure dependence of Tc is small and negative, dTc/dp = - 0.77 K/GPa, and agrees with the general trend observed in previous data.