Out of plane effect on the superconductivity of Sr2-xBaxCuO3+y with Tc up to 98K

A series of new Sr2-xBaxCuO3+y (0 x 0.6) superconductors were prepared using high-pressure and high-temperature synthesis. A Rietveld refinement based on powder x-ray diffraction confirms that the superconductors crystallize in the K2NiF4-type structure of a space group I4/mmm similar to that of La2CuO4 but with partially occupied apical oxygen sites. It is found that the superconducting transition temperature Tc of this Ba substituted Sr2CuO3+y superconductor with constant carrier doping level, i.e., constant d, is controlled not only by order/disorder of apical-O atoms but also by Ba content. Tcmax =98 K is achieved in the material with x=0.6 that reaches the record value of Tc among the single-layer copper oxide superconductors, and is higher than Tc=95K of Sr2CuO3+y with optimally ordered apical-O atoms. There is Sr-site disorder in Sr2-xBaxCuO3+y which might lead to a reduction of Tc. The result indicates that another effect surpasses the disorder effect that is related either to the increased in-plane Cu-O bond length or to elongated apical-O distance due to Ba substitution with larger cation size. The present experiment demonstrates that the optimization of local geometry out of the Cu-O plane can dramatically enhance Tc in the cuprate superconductors.Comment: 23 Pages, 1 Table, 5 Figure

Enhancement of magnetoresistance in manganite multilayers

Magnanite multilayers have been fabricated using La0.67Ca0.33MnO3 as the ferromagnetic layer and Pr0.7Ca0.3MnO3 and Nd0.5Ca0.5MnO3 as the spacer layers. All the multilayers were grown on LaAlO3 (100) by pulse laser deposition. An enhanced magnetoresistnace (defined (RH- R0)/R0) of more than 98% is observed in these multilayers. Also a low field magnetoresistance of 41% at 5000 Oe is observed in these multilayer films. The enhanced MR is attributed to the induced double exchange in the spacer layer, which is giving rise to more number of conducting carriers. This is compared by replacing the spacer layer with LaMnO3 where Mn exists only in 3+ state and no enhancement is observed in the La0.67Ca0.33MnO3 / LaMnO3 multilayers as double exchange mechanism can not be induced by external magnetic fields.Comment: 13 pages, 5 Figure

Quantum Communication Through a Spin-Ring with Twisted Boundary Conditions

We investigate quantum communication between the sites of a spin-ring with twisted boundary conditions. Such boundary conditions can be achieved by a flux through the ring. We find that a non-zero twist can improve communication through finite odd numbered rings and enable high fidelity multi-party quantum communication through spin rings (working near perfectly for rings of 5 and 7 spins). We show that in certain cases, the twist results in the complete blockage of quantum information flow to a certain site of the ring. This effect can be exploited to interface and entangle a flux qubit and a spin qubit without embedding the latter in a magnetic field.Comment: four pages two figure

Hawking radiation from the Schwarzschild black hole with a global monopole via gravitational anomaly

Hawking flux from the Schwarzschild black hole with a global monopole is obtained by using Robinson and Wilczek's method. Adopting a dimension reduction technique, the effective quantum field in the (3+1)--dimensional global monopole background can be described by an infinite collection of the (1+1)--dimensional massless fields if neglecting the ingoing modes near the horizon, where the gravitational anomaly can be cancelled by the (1+1)--dimensional black body radiation at the Hawking temperature.Comment: 4 pages, no figure, 3nd revsion with one reference adde

Determination of Intrinsic Ferroelectric Polarization in Orthorhombic Manganites with E-type Spin Order

By directly measuring electrical hysteresis loops using the Positive-Up Negative-Down (PUND) method, we accurately determined the remanent ferroelectric polarization Pr of orthorhombic RMnO3 (R = Ho, Tm, Yb, and Lu) compounds below their E-type spin ordering temperatures. We found that LuMnO3 has the largest Pr of 0.17 uC/cm^2 at 6 K in the series, indicating that its single-crystal form can produce a Pr of at least 0.6 \muuC/cm^2 at 0 K. Furthermore, at a fixed temperature, Pr decreases systematically with increasing rare earth ion radius from R = Lu to Ho, exhibiting a strong correlation with the variations in the in-plane Mn-O-Mn bond angle and Mn-O distances. Our experimental results suggest that the contribution of the Mn t2g orbitals dominates the ferroelectric polarization.Comment: 16 pages, 4 figure