Showing papers by "Douglas J. Scalapino published in 1998"

Density Matrix Renormalization Group Study of the Striped Phase in the 2D t − J Model

Abstract: Using the density matrix renormalization group, we study the 2D $t\ensuremath{-}J$ model at a hole doping of $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\frac{1}{8}$ on clusters as large as $19\ifmmode\times\else\texttimes\fi{}8$. We find a striped phase consistent with recent neutron scattering experiments. We find that bond-centered and site-centered stripes have nearly the same energy, suggesting that in the absence of pinning effects the domain walls can fluctuate.

Energetics of Domain Walls in the 2D t-J Model

Abstract: Using the density matrix renormalization group, we calculate the energy of a domain wall in the 2D t-J model as a function of the linear hole density \rho_\ell, as well as the interaction energy between walls, for J/t=0.35. Based on these results, we conclude that the ground state always has domain walls for dopings 0 0.17, there are only walls with \rho_\ell =1. For \rho_\ell = 1, diagonal (1,1) domain walls have very nearly the same energy as (1,0) domain walls.

Superconducting condensation energy and an antiferromagnetic exchange-based pairing mechanism

Abstract: For the traditional low-${T}_{c}$ superconductors, the superconducting condensation energy is proportional to the change in energy of the ionic lattice between the normal and superconducting state, providing a clear link between pairing and the electron-ion interaction. Here, for the $t\ensuremath{-}J$ model, we discuss an analogous relationship between the superconducting condensation energy and the change in the exchange energy between the normal and superconducting states. We point out the possibility of measuring this using neutron scattering and note that such a measurement, while certainly difficult, could provide important evidence for an exchange interaction-based pairing mechanism.

SO(5) symmetric ladder

Abstract: We construct an SO(5) symmetric electron model on a two-chain ladder with purely local interactions on a rung. The ground state phase diagram of this model is determined in the strong-coupling limit. The relationship between the spin-gap magnon mode of the spin-gap insulator and the $\ensuremath{\pi}$ resonance mode of the $d$-wave pairing phase is discussed. We also present the exact ground state for an SO(5) superspin model.

Intrinsic limits on the Q and intermodulation of low power high temperature superconducting microstrip resonators

Abstract: Cuprate superconducting thin films are being used to make compact low power microwave devices. In recent years, with improved materials and designs, there has been a steady improvement in device performance, notably an increase in resonator Q and a decrease in the nonlinear intermodulation. It is important to understand how much improvement can be expected. Here we discuss the intrinsic limiting behavior that one might achieve with a perfect film, review the present status, and discuss what the limiting behavior implies for high temperature superconducting filters. Our analysis indicates that increases in unloaded Q to ∼106 and decreases in intermodulation by a factor of ∼104, compared with today’s values, might be achieved.

Comparison of different ladder models

Abstract: Using density matrix renormalization group calculations, we compare results obtained for the $t\ensuremath{-}J,$ one-band Hubbard, and three-band Hubbard models of a two-leg CuO ladder. Spin and charge gaps, pair binding energies, and effective pair hoppings are calculated for a wide range of parameters. All three models have an insulating state at a filling corresponding to one hole per Cu site. For physically relevant parameters their spin gaps are similar in size but they exhibit quite different charge gaps. We find that the binding energy of a pair of doped holes is of the order of the undoped ladder spin gap for all three models. The main difference between the models is the size of the effective pair hopping, which is significantly larger in the three-band model with parameters appropriate for CuO materials than in the other two models.

Microwave loss and intermodulation in Tl(2)Ba(2)CaCu(2)O(y) thin films

Abstract: A superconducting microstrip hairpin resonator is used as a tool to study the linear and nonlinear microwave response of TBCCO thin films. We extract the surface resistance R(S)(T), penetration depth lambda(T), and intermodulation critical current J(IMD)(T) for such a resonator at 4.2 GHz. The surface impedance results compare well with cavity perturbation measurements on portions of the same wafer. J(IMD)(T) is compared against theoretical models for the intrinsic nonlinear response of s- and d-wave superconductors. We demonstrate that the de critical current J(c) and J(IMD) are distinct material parameters, describing different physical regimes.

Ground-state properties of the doped three-leg t-j ladder

Abstract: Results for a doped three-leg $t$-$J$ ladder obtained using the density-matrix renormalization group are reported. At low hole doping, the holes form a dilute gas with a uniform density. The momentum occupation of the odd band shows a sharp decrease at a large value of ${k}_{F}$ similar to the behavior of a lightly doped $t$-$J$ chain, while the even modes appear gapped. The spin-spin correlations decay as a power law consistent with the absence of a spin gap, but the pair-field correlations are negligible. At larger doping we find evidence for a spin gap and as $x$ increases further we find three-hole diagonal domain walls. In this regime there are significant pair-field correlations and the internal pair orbital has ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-like symmetry.