Coexistence of magnetism and superconductivity in a t-J bilayer

We investigate coexistence of antiferromagnetic and superconducting correlations in bilayered materials using a two-dimensional t-J model with couplings across the layers using variational Monte Carlo calculations. It is found that the underdoped regime supports a coexisting phase, beyond which the (d-wave) superconducting state becomes stable. Further, the effects of interplanar coupling parameters on the magnetic and superconducting correlations as a function of hole doping are studied in details. The magnetic correlations are found to diminish with increasing interplanar hopping away from half filling, while the exchange across the layers strengthens interplanar antiferromagnetic correlations both at and away from half filling. The superconducting correlations show more interesting features where larger interplanar hopping considerably reduces planar correlations at optimal doping, while an opposite behaviour, i.e. stabilisation of the superconducting state is realised in the overdoped regime, with the interplanar exchange all the while playing a dormant role.Comment: 8 pages, 9 figures, RevTex4, Submitted to Phys. Rev.

Enhancement of Aluminum Alloy Forgings through Rapid Billet Heating

Forging is a manufacturing process in which metal is pressed, pounded or squeezed under great pressure and, often, under high strain rates into high-strength parts known as forgings. The process is typically performed hot by preheating the metal to a desired temperature before it is worked. The forging process can create parts that are stronger than those manufactured by any other metal working process. Forgings are almost always used where reliability and human safety are critical. Forgings are normally component parts contained inside assembled items such airplanes, automobiles, tractors, ships, oil drilling equipment, engines missiles, and all kinds of capital equipment Forgings are stronger than castings and surpass them in predictable strength properties, producing superior strength that is assured, part to part

A SCHEME FOR REPRESENTATION-MATRICES OF A PERMUTATION GROUP USING SPIN-PAIRED FUNCTIONS

In the present note, a linked form of spin-paired functions for an N-electron system in spin state S is suggested. This is found to lead to a simple scheme for generating the representation matrices of the elements of permutation group without searching for linkages in the superposition diagrams. The program based on this is found to generate the representation matrices more efficiently than do currently available procedures

CONFIGURATION-INTERACTION STUDIES USING BIORTHOGONAL APPROACH TO VB BASIS

In the present article, we have attempted a systematic procedure for use of biorthogonal techniques to the configuration interaction studies in molecules using nonorthogonal valence bond (VB) orbitals. The procedure developed is integral-driven and a program based on this has been developed. Test runs of the program have been carried out in case of full and truncated configuration spaces. (C) 1995 John Wiley and Sons, Inc

Schottky defect enthalpies of alkaline earth oxides

306-312<span style="font-size:14.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:black;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">The Schottky defect formation process in MgO, CaO, SrO, and BaO is investigated using our recently introduced EPPI model3. We find that inclusion of quadrupolar interactions makes a substantial contribution to the formation energy by values ranging from 1.2 eV to 2.9 eV. The EPPI values of the enthalpies (hfs) are 5.9, 5.8, 4.7 and 1.4 eV respectively for MgO, CaO, SrO, and BaO. The results of cation self diffusion experiments in MgO are reanalyzed to include the effects of impurity-vacancy association reaction. The analysis suggests the previous interpretation of the experimental data to be an oversimplification. Since the binding energy of an impurity - defect complex in MgO could be quite large, the effects of the association reaction on the defect densities are appreciable. On the basis of near complete association of the dominant tetravalent cation impurity, hfs in MgO is found to be 5.8 eV which is in good agreement with the theoretical value of the present work.</span

Phase diagram for a t-J bilayer: role of interlayer couplings

The phase diagram for a t-J bilayer as a function of interplanar hopping, t⊥ and hole concentration, x is presented for a few different values of interplanar exchange, J⊥ using variational Monte Carlo calculations. The phase diagram shows rich features, such as a coexistence of antiferromagnetism and superconductivity at underdoping, planar (d-wave) and interplanar (dz-wave) superconducting correlations for small and large J⊥, respectively at optimal and overdoping. Another unusual feature appears in the form of a dome shaped structure in the phase diagram where the superconducting correlations are initially assisted as interplanar hopping is enhanced for small t⊥, while larger t⊥ is found to be detrimental to superconductivity