Title: Inhomogeneous Charge Textures Stabilized by Electron-Phonon Interactions in the t-J Model

We study the effect of diagonal and off-diagonal electron-phonon coupling in the ground state properties of the t-J model. Adiabatic and quantum phonons are considered using Lanczos techniques. Charge tiles and stripe phases with mobile holes (localized holes) are observed at intermediate (large) values of the diagonal electron-phonon coupling. The stripes are stabilized by half-breathing modes, while the tiles arise due to the development of extended breathing modes. Off-diagonal terms destabilize the charge inhomogeneous structures with mobile holes by renormalizing the diagonal coupling but do not produce new phases. Buckling modes are also studied and they seem to induce amore » gradual phase separation between hole rich and hole poor regions. The pairing correlations are strongly suppressed when the holes are localized. However, in charge inhomogeneous states with mobile holes no dramatic changes, compared with the uniform state, are observed in the pairing correlations indicating that D-wave pairing and moderate electron-phonon interactions can coexist.« less

We present the zero-temperature phase diagram of the one-dimensional t{sub 2g}-orbital Hubbard model, obtained using the density-matrix renormalization group and Lanczos techniques. Emphasis is given to the case of the electron density n=5 corresponding to five electrons per site, while several other cases for electron densities between n=3 and 6 are also studied. At n=5, our results indicate a first-order transition between a paramagnetic (PM) insulator phase, with power-law slowly decaying correlations, and a fully polarized ferromagnetic (FM) state by tuning the Hund's coupling. The results also suggest a transition from the n=5 PM insulator phase to a metallic regimemore » by changing the electron density, either via hole or electron doping. The behavior of the spin, charge, and orbital correlation functions in the FM and PM states are also described in the text and discussed. The robustness of these two states against varying parameters suggests that they may be of relevance in quasi-one-dimensional Co-oxide materials, or even in higher dimensional cobaltite systems as well.« less

We present an exact diagonalization study of the dynamical spin and density correlation functions in small clusters of the {ital t}-{ital J} model, focusing on the regime of intermediate and low electron densities, {rho}{sub {ital e}}{lt}0.5. In two dimensions (2D) both correlation functions agree remarkably well with the convolution of the single-particle spectral function, i.e., the simplest estimate possible within a Fermi-liquid picture. Deviations from the convolution are shown to originate from symmetry-related selection rules, which are unaccounted for in the convolution estimate. For all fillngs under consideration, we show that the low-energy peaks originate from particle-hole excitations between themore » Fermi momenta, as expected for a Fermi liquid. We contrast this with the behavior in 1D, where spin and density correlation function show the differences characteristic of spin-charge separation and where neither correlation function is approximated well by the convolution.« less

We study the properties of A-italic/sub F-italic//sub B-italic//sup b-italic//sup ,//sup t-italic/, the forward-backward asymmetry, and of A-italic/sub pol//sub F-italic//sub B-italic//sup b-italic//sup ,//sup t-italic/, the polarized forward-backward asymmetry, for the processes e-italic/sup +/e/sup -/..-->..Z/sup 0/..-->..b-barb,t-italic t-italic-bar in the presence of new gauge interactions. It turns out that a measurement of A-italic/sub pol//sub F-italic//sub B-italic//sup b-italic/ can determine the strength of B-italic/sup 0/-B-bar /sup 0/ mixing without any appreciable impact from new gauge interactions. A measurement of A-italic/sub F-italic//sub B-italic//sup b-italic/ has the potential to reveal such new forces, however only in a semiquantitative fashion unless B-italic/sup 0/-B-bar /sup 0/ mixing ismore » well determined in an independent way. On the other hand A-italic/sub F-italic//sub B-italic//sup t-italic/ can quantitatively measure the effects of new currents, because T-italic/sup 0/-T-bar /sup 0/ mixing is expected to be very small. We show that the additional kinematic factors which appear in expression for A-italic/sub F-italic//sub B-italic//sup t-italic/ do not suppress the effects of new gauge structures.« less

Single rotational states were populated in vibrationally excited hydrogen by stimulated Raman pumping. The population in H/sub 2/ X-italic /sup 1/summation/sup +//sub g-italic/(v-italic'' = 0,1) and D/sub 2/ X-italic /sup 1/summation/sup +//sub g-italic/(v-italic'' = 0,1) was probed state selectively by tunable vacuum ultraviolet (VUV) laser radiation around lambda = 110 nm, and the fluorescence induced when exciting the hydrogen molecules in the (0--0), (1--0), (2--0), (3--1), and (4--1) Lyman bands of the (B-italic /sup 1/summation/sup +//sub u-italic/X-italic /sup 1/summation/sup +//sub g-italic/) transition monitored. From a comparison of line heights, the stimulated Raman pumping efficiency is estimated to be 30%--50% inmore » the focal volume. Rotational transitions in X-italic /sup 1/summation/sup +//sub g-italic/(v-italic'' = 1) were induced in collisions with H/sub 2/, D/sub 2/, and He. State-to-state rotational relaxation rates were measured for the (J-italic'' = 1..-->..J-italic'' = 3) transition in H/sub 2/(v-italic'' = 1) and for the (J-italic'' = 2..-->..J-italic'' = 0,4) transitions in D/sub 2/(v-italic'' = 1). These rates were found to be generally higher than the corresponding previously determined ones in ground state hydrogen, in qualitative accord with recent theoretical calculations. A comparison with available theoretical state-to-state cross sections shows that the rates obtained with these cross sections are generally lower than the relaxation rates directly measured in this work.« less