Local Antiferromagnetic Correlations and dx2−y2d_{x^2-y^2} Pairing

The high $T_c$ cuprate superconductors doped near half-filling have short range antiferromagnetic correlations. Here we describe an intuitive local picture of why, if pairing occurs in the presence of short-range antiferromagnetic correlations, the orbital state will have $d_{x^2-y^2}$ symmetry.Comment: 8 pages and one figur

Dynamical properties of the single--hole tt--JJ model on a 32--site square lattice

We present results of an exact diagonalization calculation of the spectral function $A(\bf k, \omega)$ for a single hole described by the $t$--$J$ model propagating on a 32--site square cluster. The minimum energy state is found at a crystal momentum ${\bf k} = ({\pi\over 2}, {\pi\over 2})$, consistent with theory, and our measured dispersion relation agrees well with that determined using the self--consistent Born approximation. In contrast to smaller cluster studies, our spectra show no evidence of string resonances. We also make a qualitative comparison of the variation of the spectral weight in various regions of the first Brillouin zone with recent ARPES data.Comment: 10 pages, 5 postscript figures include

Induced polarization at a paraelectric/superconducting interface

We examine the modified electronic states at the interface between superconducting and ferro(para)-electric heterostructures. We find that electric polarization $P$ and superconducting $\psi$ order parameters can be significantly modified due to coupling through linear terms brought about by explicit symmetry breaking at the interface. Using an effective action and a Ginzburg-Landau formalism, we show that an interaction term linear in the electric polarization will modify the superconducting order parameter $\psi$ at the interface. This also produces modulation of a ferroelectric polarization. It is shown that a paraelectric-superconductor interaction will produce an interface-induced ferroelectric polarization.Comment: 4 pages, 3 figures, Submitted to Phys. Rev.

Polaronic transport induced by competing interfacial magnetic order in a La0.7_{0.7}Ca0.3_{0.3}MnO3_{3}/BiFeO3_{3} heterostructure

Using ultrafast optical spectroscopy, we show that polaronic behavior associated with interfacial antiferromagnetic order is likely the origin of tunable magnetotransport upon switching the ferroelectric polarity in a La$_{0.7}$Ca$_{0.3}$MnO$_{3}$/BiFeO$_{3}$ (LCMO/BFO) heterostructure. This is revealed through the difference in dynamic spectral weight transfer between LCMO and LCMO/BFO at low temperatures, which indicates that transport in LCMO/BFO is polaronic in nature. This polaronic feature in LCMO/BFO decreases in relatively high magnetic fields due to the increased spin alignment, while no discernible change is found in the LCMO film at low temperatures. These results thus shed new light on the intrinsic mechanisms governing magnetoelectric coupling in this heterostructure, potentially offering a new route to enhancing multiferroic functionality

Validity of the rigid band picture for the t-J model

We present an exact diagonalization study of the doping dependence of the single particle Green's function in 16, 18 and 20 site clusters of t-J model. We find evidence for rigid-band behaviour starting from the half-filled case: upon doping, the topmost states of the quasiparticle band observed in the photoemisson spectrum at half-filling cross the chemical potential and reappear as the lowermost states of the inverse photoemission spectrum. Features in the inverse photoemission spectra which are inconsistent with rigid-band behaviour are shown to originate from the nontrivial point group symmetry of the ground state with two holes, which enforces different selection rules than at half-filling. Deviations from rigid band behaviour which lead to the formation of the `large Fermi surface' in the momentum distribution occur only at energies far from the chemical potential. A Luttinger Fermi surface and a nearest neighbor hopping band do not exist.Comment: Remarks: Revtex file + 7 figures attached as compressed postscript files Figures can also be obtained by ordinary mail on reques