[en] The one-dimensional electron gas exhibits spin-charge separation and power-law spectral responses to many experimentally relevant probes. Ordering in a quasi-one-dimensional system is necessarily associated with a dimensional crossover, at which sharp quasiparticle peaks, with small spectral weight, emerge from the incoherent background. Using methods of Abelian bosonization, we derive asymptotically correct expressions for the spectral changes induced by this crossover. Comparison is made with experiments on the high-temperature superconductors, which are electronically quasi-one-dimensional on a local scale. (c) 2000 The American Physical Society

[en] We have carried out extensive first-principles angle-resolved photointensity (ARPES) simulations in Bi2212 wherein the photoemission process is modeled realistically by taking into account the full crystal wave functions of the initial and final states in the presence of the surface. The spectral weight of the ARPES feature associated with the CuO₂ plane bands is found to undergo large and systematic variations with k_{(parallelsign)} as well as the energy and polarization of the incident photons. These theoretical predictions are in good accord with the corresponding measurements, indicating that the remarkable observed changes in the spectral weights in Bi2212 are essentially a matrix element effect and that the importance of matrix elements should be kept in mind in analyzing the ARPES spectra in the high T_c 's. (c) 1999 The American Physical Society

[en] It is shown that the complex d_xy component is generated in a d-wave superconductor in the magnetic field. As one enters a superconducting state at the finite field the normal to superconducting transition occurs into the bulk d_x²-y²+id_xy state. The driving force for the transition is the linear coupling between the magnetic field and the nonzero magnetization of the d_x²-y²+id_xy condensate. The external magnetic field violates parity and time-reversal symmetries and the nodal quasiparticle states respond by generating the id_xy component of the order parameter, with the magnitude estimated to be on the order of a few kelvin. Parity (P) and time-reversal (T) symmetries are violated in this state. (c) 2000 The American Physical Society

[en] We calculate the dependence of the interlayer quasiparticle conductivity, σ_q , in a Josephson coupled d -wave superconductor on the magnetic field B (parallel sign) c and the temperature T . We consider a clean superconductor with resonant impurity scattering and a dominant coherent interlayer tunneling. When pancake vortices in adjacent layers are weakly correlated, at low T the conductivity increases sharply with B over a field scale determined by the impurity scattering, before reaching an extended region of slow linear growth. At high T the conductivity initially decreases and then reaches the same linear regime. For correlated pancakes, σ_q increases much more strongly with the applied field. (c) 2000 The American Physical Society

[en] We demonstrate that pinning strongly renormalizes both longitudinal and Hall resistivity in the flux flow regime. Using a simple model for the pinning potential we show that the magnitude of the vortex contribution to the Hall voltage decreases with increase in the pinning strength. The Hall resistivity ρ_xy scales as ρ²_xx only for a weak pinning. On the contrary, a strong pinning breaks the scaling relation and can even result in a sign reversal of ρ_xy . (c) 1999 The American Physical Society

[en] A spectrometer incorporating a high transition temperature dc superconducting quantum interference device (SQUID) is used to obtain nuclear magnetic resonance signals from protons in mineral oil at room temperature in fields up to 3 mT. The spatial separation between the SQUID magnetometer at 77 K and the sample at room temperature is less than 1 mm. At 2 mT, the signal is easily resolved in a single scan. Two-dimensional images of samples consisting of pieces of lucite or glass immersed in mineral oil are obtained at 2 mT. (c) 1999 American Institute of Physics

[en] In this letter, we present results of experiments in which nuclear magnetic resonance (NMR) signals were detected using an untuned pickup coil coupled to a high temperature superconductor (HTS) based superconducting quantum interference device (SQUID). We were able to operate the HTS SQUID in the presence of static fields of up to 500 Gauss and radio frequency fields of up to 6 Gauss. The ability of a HTS SQUID to detect NMR signals opens up the possibility of using a sensitive detector for practical applications involving NMR that require a broad detection bandwidth. copyright 1997 American Institute of Physics

[en] We propose two new geometries for Josephson junction experiments between the edge of an orthorhombic, untwinned single-crystal high-T_c superconductor, assumed to have an order parameter of the mixed s±d_x²-y² variety, and a conventional, s-wave superconductor. The first geometry is a straight-edge Josephson junction cut at an angle φ₀ with respect to the a-axis edge of a high-T_c crystal. We studied the effects of a regular array of a/b steps comprising the edge upon the I_c(B) pattern for different φ₀ values. Varying φ₀ can elucidate the locations of any purported order-parameter nodes. The second geometry is a disk cut from a high-T_c single crystal, with a Josephson junction formed on the edge, centered at φ₀, with an angular width of Δφ. The case Δφ=π is nearly free of systematic flux trapping problems, and is shown to be particularly important in quantifying the precise amount of s/d order-parameter mixing. Smaller Δφ values can also be useful in locating the purported order-parameter nodes. copyright 1997 The American Physical Society

[en] Little is known about the impact of the electron-photon matrix element on angle-resolved photoelectron spectra of layered cuprate compounds. Using the example of the model layered cuprate Sr₂CuO₂Cl₂, we demonstrate that the electron-photon matrix element has a significant influence on energy distribution curves, rendering their interpretation as images of the spectral function nontrivial. (c) 2000 The American Physical Society

[en] The stability of a vortex glass phase with quasi-long-range positional order is examined for a disordered layered superconductor. The role of topological defects is investigated using a scaling argument supplemented by a variational calculation. The results indicate that topological order is preserved for some range of parameters in the vortex glass phase. The stability regime is given in terms of a simple Lindemann-like criterion and is consistent with recent experiments. copyright 1997 The American Physical Society