Evidence of Electron Fractionalization from Photoemission Spectra in the High Temperature Superconductors

In the normal state of the high temperature superconductors Bi_2Sr_2CaCu_2O_{8+delta} and La_{2-x}Sr_{x}CuO_4, and in the related ``stripe ordered'' material La_1.25Nd_0.6Sr_0.15CuO_4, there is sharp structure in the measured single hole spectral function A(k,w) considered as a function of k at fixed small binding energy w. At the same time, as a function of w at fixed k on much of the putative Fermi surface, any structure in A(k,w), other than the Fermi cutoff, is very broad. This is characteristic of the situation in which there are no stable excitations with the quantum numbers of the electron, as is the case in the one dimensional electron gas.Comment: Published versio

Stein hypothesis and screening effect for covariances with compact support

In spatial statistics, the screening effect historically refers to the situation when the observations located far from the predictand receive a small (ideally, zero) kriging weight. Several factors play a crucial role in this phenomenon: among them, the spatial design, the dimension of the spatial domain where the observations are defined, the mean-square properties of the underlying random field and its covariance function or, equivalently, its spectral density. The tour de force by Michael L. Stein provides a formal definition of the screening effect and puts emphasis on the Matérn covariance function, advocated as a good covariance function to yield such an effect. Yet, it is often recommended not to use covariance functions with a compact support. This paper shows that some classes of covariance functions being compactly supported allow for a screening effect according to Stein’s definition, in both regular and irregular settings of the spatial design. Further, numerical experiments suggest that the screening effect under a class of compactly supported covariance functions is even stronger than the screening effect under a Matérn model

Finite temperature Drude weight of the one dimensional spin 1/2 Heisenberg model}

Using the Bethe ansatz method, the zero frequency contribution (Drude weight) to the spin current correlations is analyzed for the easy plane antiferromagnetic Heisenberg model. The Drude weight is a monotonically decreasing function of temperature for all 0<Delta< 1, it approaches the zero temperature value with a power law and it appears to vanish for all finite temperatures at the isotropic Delta=1 point.Comment: 5 pages, 2 Postscript figure

Time evolution of a quantum many-body system: transition from integrability to ergodicity in thermodynamic limit

Numerical evidence is given for non-ergodic (non-mixing) behavior, exhibiting ideal transport, of a simple non-integrable many-body quantum system in the thermodynamic limit, namely kicked $t-V$ model of spinless fermions on a ring. However, for sufficiently large kick parameters $t$ and $V$ we recover quantum ergodicity, and normal transport, which can be described by random matrix theory.Comment: 4 pages in RevTex (6 figures in PostScript included

Evaluation of the likelihood of establishing false codling moth (Thaumatotibia leucotreta) in Australia via the international cut flower market

Kenya and some other African countries are threatened by a serious pest Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), the false codling moth. The detection of T. leucotreta is quite difficult due to the cryptic nature of the larvae during transportation and is therefore a concern for Australia. This insect is a known pest of agriculturally important crops. Here, Maxent was used to assess the biosecurity threat of T. leucotreta to Australia. Habitat suitability and risk assessment of T. leucotreta in Australia were identified based on threatened areas under suitable climatic conditions and the presence of hosts in a given habitat. Modeling indicated that Australia is vulnerable to invasion and establishment by T. leucotreta in some states and territories, particularly areas of western and southern Australia. Within these locations, the risk is associated with specific cropping areas. As such, invasion and establishment by T. leucotreta may have serious implications for Australia’s agricultural and horticultural industries e.g., the fruit and vegetable industries. This study will be used to inform the government and industry of the threat posed by T. leucotreta imported via the cut flower industry. Targeted preventative measures and trade policy could be introduced to protect Australia from invasion by this pest

In vivo characterization of distinct modality-specific subsets of somatosensory neurons using GCaMP

Mechanistic insights into pain pathways are essential for a rational approach to treating this vast and increasing clinical problem. Sensory neurons that respond to tissue damage (nociceptors) may evoke pain sensations and are typically classified on the basis of action potential velocity. Electrophysiological studies have suggested that most of the C-fiber nociceptors are polymodal, responding to a variety of insults. In contrast, gene deletion studies in the sensory neurons of transgenic mice have frequently resulted in modality-specific deficits. We have used an in vivo imaging approach using the genetically encoded fluorescent calcium indicator GCaMP to study the activity of dorsal root ganglion sensory neurons in live animals challenged with painful stimuli. Using this approach, we can visualize spatially distinct neuronal responses and find that >85% of responsive dorsal root ganglion neurons are modality-specific, responding to either noxious mechanical, cold, or heat stimuli. These observations are mirrored in behavioral studies of transgenic mice. For example, deleting sodium channel Nav1.8 silences mechanical- but not heat-sensing sensory neurons, consistent with behavioral deficits. In contrast, primary cultures of axotomized sensory neurons show high levels of polymodality. After intraplantar treatment with prostaglandin E2, neurons in vivo respond more intensely to noxious thermal and mechanical stimuli, and additional neurons (silent nociceptors) are unmasked. Together, these studies define polymodality as an infrequent feature of nociceptive neurons in normal animals

Inherent Inhomogeneities in Tunneling Spectra of BSCCO Crystals in the Superconducting State

Scanning Tunneling Spectroscopy on cleaved BSCCO(2212) single crystals reveal inhomogeneities on length-scales of $\sim$30 $\AA$. While most of the surface yields spectra consistent with a d-wave superconductor, small regions show a doubly gapped structure with both gaps lacking coherence peaks and the larger gap having a size typical of the respective pseudo-gap for the same sample.Comment: 4 pages, 4 figure

Luther-Emery Stripes, RVB Spin Liquid Background and High Tc Superconductivity

The stripe phase in high Tc cuprates is modeled as a single stripe coupled to the RVB spin liquid background by the single particle hopping process. In normal state, the strong pairing correlation inherent in RVB state is thus transfered into the Luttinger stripe and drives it toward spin-gap formation described by Luther-Emery Model. The establishment of global phase coherence in superconducting state contributes to a more relevant coupling to Luther-Emery Stripe and leads to gap opening in both spin and charge sectors. Physical consequences of the present picture are discussed, and emphasis is put on the unification of different energy scales relevant to cuprates, and good agreement is found with the available experimental results, especially in ARPES.Comment: 4 pages, RevTe

Reduction of three-band model for copper oxides to single-band generalized t~-~J model

A three-band model for copper oxides in the region of parameters where the second hole on the copper has energy close to the first hole on the oxygen is considered. The exact solution for one hole on a ferromagnetic background of the ordered copper spins is obtained. A general procedure for transformation of the primary Hamiltonian to the Hamiltonian of singlet and triplet excitations is proposed. Reduction of the singlet-triplet Hamiltonian to the single-band Hamiltonian of the generalized t~-~J model is performed. A comparison of the solution for the generalized t~-~J model on a ferromagnetic background with the exact solution shows a very good agreement.Comment: 20 pages (LATEX

The Roton Fermi Liquid

We introduce and analyze a novel metallic phase of two-dimensional (2d) electrons, the Roton Fermi Liquid (RFL), which, in contrast to the Landau Fermi liquid, supports both gapless fermionic and bosonic quasiparticle excitations. The RFL is accessed using a re-formulation of 2d electrons consisting of fermionic quasiparticles and $hc/2e$ vortices interacting with a mutual long-ranged statistical interaction. In the presence of a strong vortex-antivortex (i.e. roton) hopping term, the RFL phase emerges as an exotic yet eminently tractable new quantum ground state. The RFL phase exhibits a ``Bose surface'' of gapless roton excitations describing transverse current fluctuations, has off-diagonal quasi-long-ranged order (ODQLRO) at zero temperature (T=0), but is not superconducting, having zero superfluid density and no Meissner effect. The electrical resistance {\it vanishes} as $T \to 0$ with a power of temperature (and frequency), $R(T) \sim T^\gamma$ (with $\gamma >1$), independent of the impurity concentration. The RFL phase also has a full Fermi surface of quasiparticle excitations just as in a Landau Fermi liquid. Electrons can, however, scatter anomalously from rotonic "current fluctuations'' and "superconducting fluctuations'', leading to "hot" and "cold" spots. Fermionic quasiparticles dominate the Hall electrical transport. We also discuss instabilities of the RFL to a conventional Fermi liquid and a superconductor. Precisely {\it at} the instability into the Fermi liquid state, the exponent $\gamma =1$, so that $R(T) \sim T$. Upon entering the superconducting state the anomalous quasiparticle scattering is strongly suppressed. We discuss how the RFL phenomenology might apply to the cuprates.Comment: 43 page