Failure of Scattering Interference in the Pseudogap State of Cuprate Superconductors

We calculate scattering interference patterns for various electronic states proposed for the pseudogap regime of the cuprate superconductors. The scattering interference models all produce patterns whose wavelength changes as a function of energy, in contradiction to the energy-independent wavelength seen by scanning tunneling microscopy (STM) experiments in the pseudogap state. This suggests that the patterns seen in STM local density of states measurements are not due to scattering interference, but are rather the result of some form of ordering.Comment: To be submitted to Phys. Rev.

Inhomogeneous states with checkerboard order in the t-J Model

We study inhomogeneous states in the t-J model using an unrestricted Gutzwiller approximation. We find that $pa\times pa$ checkerboard order, where $p$ is a doping dependent number, emerges from Fermi surface instabilities of both the staggered flux phase and the Fermi liquid state with realistic band parameters. In both cases, the checkerboard order develops at wave vectors $(\pm 2\pi/pa,0)$, $(0,\pm2\pi/pa)$ that are tied to the peaks of the wave-vector dependent susceptibility, and is of the Lomer-Rice-Scott type. The properties of such periodic, inhomogeneous states are discussed in connection to the checkerboard patterns observed by STM in underdoped cuprates.Comment: Published Versio

Surface pinning of fluctuating charge order: an "extraordinary" surface phase transition

We study the mean-field theory of charge-density wave (CDW) order in a layered system, including the effect of the long-range Coulomb interaction and of screening by uncondensed electrons. We particularly focus on the conditions necessary for an ``extraordinary'' transition, in which the surface orders at a higher temperature, and is more likely to be commensurate, than the bulk. We interpret recent experiments on NaCCOC as indicating the presence of commensurate CDW at the surface that is not present in the bulk. More generally, we show that poor screening of the Coulomb interaction tends to stabilize incommensurate order, possibly explaining why the CDW order in LSCO and NbSe2 remains incommensurate to T -> 0, despite the small magnitude of the incommensurability.Comment: 9 pages, no figures, 31 references; 1 new figure and minor editing of the tex

Many-Impurity Effects in Fourier Transform Scanning Tunneling Spectroscopy

Fourier transform scanning tunneling spectroscopy (FTSTS) is a useful technique for extracting details of the momentum-resolved electronic band structure from inhomogeneities in the local density of states due to disorder-related quasiparticle scattering. To a large extent, current understanding of FTSTS is based on models of Friedel oscillations near isolated impurities. Here, a framework for understanding many-impurity effects is developed based on a systematic treatment of the variance Delta rho^2(q,omega) of the Fourier transformed local density of states rho(q,\omega). One important consequence of this work is a demonstration that the poor signal-to-noise ratio inherent in rho(q,omega) due to randomness in impurity positions can be eliminated by configuration averaging Delta rho^2(q,omega). Furthermore, we develop a diagrammatic perturbation theory for Delta rho^2(q,omega) and show that an important bulk quantity, the mean-free-path, can be extracted from FTSTS experiments.Comment: 7 pages, 5 figures. A version of the paper with high resolution, colour figures is available at http://www.trentu.ca/physics/batkinson/FTSTS.ps.gz minor revisions in response to refree report + figure 5 is modifie

Modeling of fluid flow in pipeline and the difference scheme stability investigation

A mathematical model of viscous fluid flow in the pipeline with the presence of flow across the surface and the narrowing of pipeline section, which is based on a system of Navier-Stokes equations in two-dimensional rectangular region with a special type of boundary conditions has been designed. The geometric configuration of the leakage zone is taken into the account. It is believed that the fluid motion is under the influence of constant length of pressure difference. For the solving of this system, the numerical method of finite differences was developed by which the finite differences scheme is realized – the first step is implicit in longitudinal coordinate, and the second – on the transversal. The study on the stability of the spectral features method, stability conditions are established for the case of flow calculation with specified parameters and for the given type of the pipeline geometry. The criterion of numerical stability is presented taking to account the model’s parameters.Побудовано математичну модель течії в’язкої рідини в трубопроводі за наявності перетікання рідини через поверхню та звуження поперечного перерізу, яка базується на системі рівнянь Нав’є – Стокса в двовимірній прямокутній системі координат зі спеціальним типом граничних умов. Враховано просторову конфігурацію зон перетікання. Рух рідини здійснюється під дією постійного перепаду тиску по довжині труби. Для розв’язання задачі використано метод скінчених різниць, розроблено чисельний метод його реалізації – перший крок ітераційного процесу здійснюється по повздовжній, другий – по поперечній координатах. Вивчення стійкості проводиться за спектральною ознакою, встановлено умови стійкості для розрахунку течії зі спеціальними параметрами і для заданого типу геометрії труби. Критерії стійкості розрахунків представлено з урахуванням параметрів моделі.Построено математическую модель течения вязкой жидкости в трубопроводе при наличии перетекания жидкости через поверхность и сужения поперечного сечения, основанная на использовании двухмерной системе уравнений Навье – Стокса в прямоугольной системе координат со специальным типом граничних условий. Учтена пространственная конфигурация зон перетекания. Движение жидкости обусловлено постоянным перепадом давления по длине трубы. Для решения задачи используется метод конечних різностей, создан численный метод его реализации – первуй шаг итерационного процесса осуществляется по продольной, второй – по поперечной координатах. Изучение устойчивости проводится с использованим спектрального признака устойчивости, установлены условия устойчивости для расч.та течений со специальными параметрами и для данного типа геометрии трубы. Критерии устойчивости представлены с уч.том параметров модели

Local edge modes in doped cuprates with checkerboard polaronic heterogeneity

We study a periodic polaronic system, which exhibits a nanoscale superlattice structure, as a model for hole-doped cuprates with checkerboard-like heterogeneity, as has been observed recently by scanning tunneling microscopy (STM). Within this model, the electronic and phononic excitations are investigated by applying an unrestricted Hartree-Fock and a random phase approximation (RPA) to a multiband Peierls-Hubbard Hamiltonian in two dimensions

STM/STS Study on 4a X 4a Electronic Charge Order of Superconducting Bi2Sr2CaCu2O8+d

We performed low-bias STM measurements on underdoped Bi2212 crystals, and confirmed that a two-dimensional (2D) superstructure with a periodicity of four lattice constants (4a) is formed within the Cu-O plane at T<Tc. This 4a X 4a superstructure, oriented along the Cu-O bonding direction, is nondispersive and more intense in lightly doped samples with a zero temperature pseudogap (ZTPG) than in samples with a d-wave gap. The nondispersive 4a X 4a superstructure was clearly observed within the ZTPG or d-wave gap, while it tended to fade out outside the gaps. The present results provide a useful test for various models proposed for an electronic order hidden in the underdoped region of high-Tc cuprates.Comment: 4 pages, submitted to J. Phys. Soc. Jp

Phenomenological lattice model for dynamic spin and charge fluctuations in the cuprates

Motivated by recent neutron scattering experiments on the cuprate superconductors, we present a phenomenological framework describing the dynamics of collective spin excitations coupled to charge/bond order fluctuations. Our quantum lattice model contains two order parameter fields, and can capture spin excitations both in broken-symmetry states with static lattice modulations, as well as in homogeneous states where the charge/bond order is fluctuating. We present results for different types of static charge/bond order, namely site- and bond-centered stripes, and plaquette modulation.Comment: 5 pages, 3 figures; Proceedings of SNS 2004, Sitges, Spai

Transport by molecular motors in the presence of static defects

The transport by molecular motors along cytoskeletal filaments is studied theoretically in the presence of static defects. The movements of single motors are described as biased random walks along the filament as well as binding to and unbinding from the filament. Three basic types of defects are distinguished, which differ from normal filament sites only in one of the motors' transition probabilities. Both stepping defects with a reduced probability for forward steps and unbinding defects with an increased probability for motor unbinding strongly reduce the velocities and the run lengths of the motors with increasing defect density. For transport by single motors, binding defects with a reduced probability for motor binding have a relatively small effect on the transport properties. For cargo transport by motors teams, binding defects also change the effective unbinding rate of the cargo particles and are expected to have a stronger effect.Comment: 20 pages, latex, 7 figures, 1 tabl

Anti-phase Modulation of Electron- and Hole-like States in Vortex Core of Bi2Sr2CaCu2Ox Probed by Scanning Tunneling Spectroscopy

In the vortex core of slightly overdoped Bi2Sr2CaCu2Ox, the electron-like and hole-like states have been found to exhibit spatial modulations in anti-phase with each other along the Cu-O bonding direction. Some kind of one-dimensionality has been observed in the vortex core, and it is more clearly seen in differential conductance maps at lower biases below +-9 mV