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.

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