High-energy kink in high-temperature superconductors

In conventional metals, electron-phonon coupling, or the phonon-mediated interaction between electrons, has long been known to be the pairing interaction responsible for the superconductivity. The strength of this interaction essentially determines the superconducting transition temperature TC. One manifestation of electron-phonon coupling is a mass renormalization of the electronic dispersion at the energy scale associated with the phonons. This renormalization is directly observable in photoemission experiments. In contrast, there remains little consensus on the pairing mechanism in cuprate high temperature superconductors. The recent observation of similar renormalization effects in cuprates has raised the hope that the mechanism of high temperature superconductivity may finally be resolved. The focus has been on the low energy renormalization and associated "kink" in the dispersion at around 50 meV. However at that energy scale, there are multiple candidates including phonon branches, structure in the spin-fluctuation spectrum, and the superconducting gap itself, making the unique identification of the excitation responsible for the kink difficult. Here we show that the low-energy renormalization at ~50 meV is only a small component of the total renormalization, the majority of which occurs at an order of magnitude higher energy (~350 meV). This high energy kink poses a new challenge for the physics of the cuprates. Its role in superconductivity and relation to the low-energy kink remains to be determined.Comment: 13 pages, 4 figure

Doping of a One-Dimensional Mott Insulator: Photoemision and Optical Studies of Sr2_2CuO3+δ_{3+\delta}

The spectral properties of a one-dimensional (1D) single-chain Mott insulator Sr$_2$CuO$_{3}$ have been studied in angle-resolved photoemission and optical spectroscopy, at half filling and with small concentrations of extra charge doped into the chains via high oxygen pressure growth. The single- particle gap is reduced with oxygen doping, but the metallic state is not reached. The bandwidth of the charge-transfer band increases with doping, while the state becomes narrower, allowing unambiguous observation of separated spinon and holon branches in the doped system. The optical gap is not changed upon doping, indicating that a shift of chemical potential rather than decrease of corelation gap is responsible for the apparent reduction of the photoemission gap.Comment: 4 pages, 2 figure

Program of large high perveance ionizer studies

Large porous tungsten sources of cesium ions - ionizer performance at high current densities and relation of performance to physical propertie

Evaluation of selected chemical processes for production of low-cost silicon phase 2. silicon material task, low-cost silicon solar array project

Progress from October 1, 1977, through December 31, 1977, is reported in the design of the 50 MT/year experimental facility for the preparation of high purity silicon by the zinc vapor reduction of silicon tetrachloride in a fluidized bed of seed particles to form a free flowing granular product

Sex and the Cinema: What American Pie Teaches the Young

This paper focuses upon the wildly successful blockbuster American Pie teenpics, especially American Pie 3 – the Wedding. I argue that these films, which are sited so securely within the visual and pedagogical machinery of Hollywood culture, are specifically designed to appeal to teenage male audiences, and to provide lessons in sex and romance. Movies like this are especially important as they are experienced by far more teenagers than, for example, instructional films or other classroom materials; indeed, as Henry Giroux has observed, "teens and youth learn how to define themselves outside of the traditional sites of instruction, such as the home and the school… Learning in the postmodern age is located elsewhere – in popular spheres that shape their identities, through forms of knowledge and desires that appear absent from what is taught in schools" (Giroux, 1997, p.49). In this paper I discuss whether the American Pie series is actually a "new age" effort which, via insubordinate performances of gender, contests the hegemonic field of signification which regulates the production of sex, gender and desire, or whether it is more accurately described as a retrogressive hetero-conservative opus with a veneer of sexual radicalism. In short, I intend to probe whether this filmic vector for sex education is all about the shaping of responsible, caring, vulnerable men, or is it guiding them to become just like their heterosexual, middle-class fathers? And whether, despite its riotous and raunchy advertising, American Pie really dishes up something spicy or something terribly wholesome instead

Measurement of the half-life of the T=12\frac{1}{2} mirror decay of 19^{19}Ne and its implication on physics beyond the standard model

The $\frac{1}{2}^+ \rightarrow \frac{1}{2}^+$ superallowed mixed mirror decay of $^{19}$Ne to $^{19}$F is excellently suited for high precision studies of the weak interaction. However, there is some disagreement on the value of the half-life. In a new measurement we have determined this quantity to be $T_{1/2}$ = $17.2832 \pm 0.0051_{(stat)}$ $\pm 0.0066_{(sys)}$ s, which differs from the previous world average by 3 standard deviations. The impact of this measurement on limits for physics beyond the standard model such as the presence of tensor currents is discussed.Comment: 5 pages, 3 figures, 1 tabl

Coulomb-Driven Cluster-Glass Behavior in Mn-Intercalated Ti1+yS2

We have investigated the low-temperature spin-glasslike phase in the intercalated transition-metal dichalcogenide Mn0.09Ti1.1S2. A departure from Curie–Weiss behavior in the paramagnetic regime indicated the formation of small ferromagnetically correlated clusters. The Vogel–Fulcher law provided an excellent description of relaxation times in the vicinity of the transition, showing that the glasslike phase occurs due to interaction between the clusters. Cole–Cole plots for data close to the transition were linear, which is consistent with a simple exponential distribution of cluster sizes. A Monte Carlo simulation of the dichalcogenide system, including excess self-intercalated Ti ions, gave an exponential cluster-size distribution for a relatively narrow range of concentration values of Mn and Ti ions, values that were consistent with those of the Mn0.09Ti1.1S2 sample. Strong commonality in the relaxation behavior with certain ferroelectric relaxor systems suggests underlying similarity in the microscopic structure of the clusters in both systems, which may be chainlike or quasi-one-dimensional

Electronic Structure of the Cuprate Superconducting and Pseudogap Phases from Spectroscopic Imaging STM

We survey the use of spectroscopic imaging STM to probe the electronic structure of underdoped cuprates. Two distinct classes of electronic states are observed in both the d-wave superconducting (dSC) and the pseudogap (PG) phases. The first class consists of the dispersive Bogoliubov quasiparticle excitations of a homogeneous d-wave superconductor, existing below a lower energy scale E=Delta0. We find that the Bogoliubov quasiparticle interference signatures of delocalized Cooper pairing are restricted to a k-space arc which terminates near the lines connecting k=\pm(pi/a0,0) to k=\pm(pi/a0). This arc shrinks continuously with decreasing hole density such that Luttinger's theorem could be satisfied if it represents the front side of a hole-pocket which is bounded behind by the lines between k=\pm(pi/a0,0) and k=\pm(0,pi/a0). In both phases the only broken symmetries detected for the |E|<Delta0 states are those of a d-wave superconductor. The second class of states occurs proximate to the pseudogap energy scale E=Delta1. Here the non-dispersive electronic structure breaks the expected 90o-rotational symmetry of electronic structure within each unit cell, at least down to 180o-rotational symmetry. This Q=0 electronic symmetry breaking was first detected as an electronic inequivalence at the two oxygen sites within each unit cell by using a measure of nematic (C2) symmetry. Incommensurate non-dispersive conductance modulations, locally breaking both rotational and translational symmetries, coexist with this intra-unit-cell electronic symmetry breaking at E=Delta1. Their characteristic wavevector Q is determined by the k-space points where Bogoliubov quasiparticle interference terminates and therefore changes continuously with doping. The distinct broken electronic symmetry states (Q=0 and finite Q) coexisting at E~Delta1 are found to be indistinguishable in the dSC and PG phases.Comment: 32 pages with 10 figure