Chizuko Murayama

Correlation between the pressure-induced changes in the Hall coefficient and Tc in superconducting cuprates

Abstract The pressure dependences of the superconducting transition temperature and the Hall coefficient have been studied for YBa 2 Cu 3 O 7 , YBa 2 Cu 4 O 8 , Bi 2 Sr 2 CaCu 2 O 8 , and Tl 2 Ba 2 CuO 6+ y . The pressure coefficient of T c changes from positive to negative as one goes from the underdoped to the overdoped side. The Hall coefficient has been found to decrease by ∼ 8–10%/GPa for these cuprates. Based on these results, the correlation between the pressure dependence of T c and the carrier density dependence of T c is discussed. The present results are also compared with our earlier result on La 2− x Sr x CuO 4 .

The mechanism of field-assisted silicon-glass Bonding

Abstract In order to evaluate the field-assisted bonding process, reactions during bonding are studied by measurements of current temperature surge and bonding front displacement. The current characteristics are simulated by Walliss equivalent circuit. From an emissivity calibrated temperature thermography, it is concluded that Joule heating at the interface is not the most important part of displacement of the bonding front. It is also shown that the displacement of the bonding front is a function of the square root of time. This suggests that the bonding is controlled by diffusion. A bonding mechanism is proposed.

The Strontium Content Dependence of Pressure Effect in (La1-xSrx)2CuO4

The enhancement of the superconducting transition temperature by pressure was studied up to ~1.5 GPa for samples of (La1-xSrx)2CuO4 with varying strontium content x. Simultaneously measured Hall coefficients were found to be independent of pressure in the present range, ruling out a pressure induced carrier density change as an origin of the Tc enhancement. The pressure coefficient of Tc was found roughly the same for the two regimes. i.e. for x<0.08, where Tc increases with x. and for 0.08<x<0.15 where it decreases with x. These results are discussed in the context of the current controversy over the nature of the electronic state in this class of materials.

Pressure dependence of superconducting transition temperature and of hall constant in high-Tc Cu-oxide superconductors

Abstract The pressure derivative of T c in the hole-doped superconductors having relatively lower carrier concentration is shown to change the sign from positive to negative at a certain pressure with a maximum of T c , while it is negative in the highly-doped ones, which is confirmed as a general feature in these compounds. The Hall constants of the samples YBa 2 Cu 3 O 7 , CaBaLaCu 3 O 7−y , YBa 2 Cu 4 O 8 , Bi 2 Sr 2 CaCu 2 O 8 and Tl 2 Ba 2 CuO 6+y is found to increase by about 10%/GPa which is almost the same amount that estimated by Yamada et al. from the Madelung energy calculation for YBa 2 Cu 4 O 8 .

High Pressure Study and the Critical Current of High Tc Superconductor (La0.9Sr0.1)2CuO4-y

The superconductivity of the multi-phased sample of (La0.9Sr0.1)2CuO4-y has been studied under hydrostatic pressure to 2.0 GPa and quasihydrostatic pressure to 4.2 GPa. The superconducting transition temperature (Tc) increases initially with increasing pressure. The results of the critical current and the diamagnetic susceptibility measurements, and the high sensitivity of Tc to the hydrostaticity of pressure suggest that the superconductivity of the high Tc phase in this multi-phased material is of bulk and highly anisotropic in nature, while that of the low Tc phase is of interfacial nature.

Pressure Effect on the Lattice Constant and Compressibility of a Superconductor (La0.9Sr0.1)2CuO4-y

(La0.9Sr0.1)2CuO4-y with K2NiF4-type layered structure shows a superconducting transition at 37 K. The pressure effect on the lattice constants along a- and c-axis was measured at room temperature up to 70 kbar. Compression coefficients of a- and c-axis are found to be almost of the same value of (2.5±0.4)×10-4kbar.-1

Is pressure dependence of Tc through change in carrier density

Abstract The pressure dependence of the Hall coefficient is studied for YBa 2 Cu 4 O 8 , YBa 2 Cu 3 O 7 , and Bi 2 Sr 2 CaCu 2 O 8 . The Hall coefficient decreases by ∼8–12%/GPa for these cuprates. The anomalous temperature dependence of the Hall coefficient is found to be intimately related with the occurrence of superconductivity.

Recent high pressure studies on the Cu-oxide superconductors at ISSP

The pressure derivative of Tc in some hole-doped Cu oxide compounds is shown to change the sign from positive to negative at a certain pressure with a maximum of Tc, which seems to be a general feature in these compounds.

Effect of magnetic field and high pressure on the superconductivity of the new high-Tc oxide Bi-Sr-Ca-Cu-O

The electrical resistances of the multiphase new high-Tc superconducting oxides Bi-Sr-Ca-Cu-O have been measured in the magnetic field and under hydrostatic pressure. The resistances decrease in two steps around 80 K and 110 K, which are believed to correspond to the presence of phases with different Tcs. The effect of the magnetic field on the superconductivity is similar to that in the Y-Ba-Cu-O and La-Ba(Sr)-Cu-O systems. However, the superconducting transition is not affected appreciably by the pressure. The results are deduced to be due to the anisotropic structure of the high-Tc phase.

Studies of Pressure-Induced Mott Metal-Insulator Transition of BaCoS2.

Transport, thermal and elastic properties under the hydrostatic pressure p up to 21.2 kbar have been studied on the layered compound BaCoS 2 , which exhibits the Mott insulator→metal transition wit...