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in publisher: "Stanford Linear Accelerator Center"

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AdS/QCD and Light Front Holography: A New Approximation to QCD

The combination of Anti-de Sitter space (AdS) methods with light-front holography leads to a semi-classical first approximation to the spectrum and wavefunctions of meson and baryon light-quark bound states. Starting from the bound-state Hamiltonian equation of motion in QCD, we derive relativistic light-front wave equations in terms of an invariant impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. These equat… more

Date: February 15, 2010

Creator: Brodsky, Stanley J. & de Teramond, Guy

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Angle-resolved photoemission study of the evolution of band structure and charge density wave properties in RTe3 (R= Y, La, Ce, Sm, Gd, Tb and Dy)

We present a detailed ARPES investigation of the RTe{sub 3} family, which sets this system as an ideal 'textbook' example for the formation of a nesting driven Charge Density Wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDW instabilities, from the opening of large gaps on the best nested parts of Fermi Surface (FS) (up to 0.4eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, than… more

Date: February 15, 2010

Creator: Brouet, V.; Yang, W. L.; Zhou, X. J.; Hussain, Z.; Moore, R. G.; He, R. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Bulk Superconductivity and Disorder in Single Crystals of LaFePO

We have studied the intrinsic normal and superconducting properties of the oxypnictide LaFePO. These samples exhibit bulk superconductivity and the evidence suggests that stoichiometric LaFePO is indeed superconducting, in contrast to other reports. We find that superconductivity is independent of the interplane residual resistivity {rho}{sub 0} and discuss the implications of this on the nature of the superconducting order parameter. Finally we find that, unlike T{sub c}, other properties in s… more

Date: February 15, 2010

Creator: Analytis, James G.; Chu, Jiun-Haw; Erickson, Ann S.; Kucharczyk, Chris; /Stanford U., Appl. Phys. Dept.; Serafin, Alessandro et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Determination of the phase diagram of the electron doped superconductor Ba(Fe1-xCox)2As2

Systematic measurements of the resistivity, heat capacity, susceptibility and Hall coefficient are presented for single crystal samples of the electron-doped superconductor Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2}. These data delineate an x-T phase diagram in which the single magnetic/structural phase transition that is observed for undoped BaFe{sub 2}As{sub 2} at 134 K apparently splits into two distinct phase transitions, both of which are rapidly suppressed with increasing Co concentration. … more

Date: February 15, 2010

Creator: Chu, Jiun-Haw; Analytis, James G.; Kucharczyk, Chris; Fisher, Ian R. & /Stanford U., Geballe Lab.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Electronic structure of the iron-based superconductor LaOFeP

The recent discovery of superconductivity in the so-called iron-oxypnictide family of compounds has generated intense interest. The layered crystal structure with transition metal ions in planar square lattice form and the discovery of spin-density-wave order near 130K seem to hint at a strong similarity with the copper oxide superconductors. A burning current issue is the nature of the ground state of the parent compounds. Two distinct classes of theories have been put forward depending on the… more

Date: February 15, 2010

Creator: Lu, D. H.; Yi, M.; /Stanford U., Phys. Dept. /SLAC, SSRL; Mo1, S.-K.; /Stanford U., Phys. Dept. /SLAC, SSRL /LBNL, ALS; Erickson, A. S. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Enhanced superconducting pairing interaction in indium-doped tin telluride

The ferroelectric degenerate semiconductor Sn{sub 1-{delta}}Te exhibits superconductivity with critical temperatures, T{sub c}, of up to 0.3 K for hole densities of order 10{sup 21} cm{sup -3}. When doped on the tin site with greater than x{sub c} = 1.7(3)% indium atoms, however, superconductivity is observed up to 2 K, though the carrier density does not change significantly. We present specific heat data showing that a stronger pairing interaction is present for x > x{sub c} than for x &lt… more

Date: February 15, 2010

Creator: Erickson, A.S.; Chu, J.-H.; /Stanford U., Appl. Phys. Dept. /Stanford U., Geballe Lab.; Toney, M.F.; Geballe, T.H.; Fisher, I.R. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Evidence for coupling between collective state and phonons in two-dimensional charge-density-wave systems

We report on a Raman scattering investigation of the charge-density-wave (CDW), quasi two-dimensional rare-earth tri-tellurides RTe{sub 3} (R = La, Ce, Pr, Nd, Sm, Gd and Dy) at ambient pressure, and of LaTe{sub 3} and CeTe{sub 3} under externally applied pressure. The observed phonon peaks can be ascribed to the Raman active modes for both the undistorted as well as the distorted lattice in the CDW state by means of a first principles calculation. The latter also predicts the Kohn anomaly in t… more

Date: February 15, 2010

Creator: Lavagnini, M.; Baldini, M.; Sacchetti, A.; Castro, D. Di; Delley, B.; Monnier, R. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Fermi Surface Evolution Across Multiple Charge Density Wave Transitions in ErTe3

The Fermi surface (FS) of ErTe{sub 3} is investigated using angle-resolved photoemission spectroscopy (ARPES). Low temperature measurements reveal two incommensurate charge density wave (CDW) gaps created by perpendicular FS nesting vectors. A large {Delta}{sub 1} = 175 meV gap arising from a CDW with c* - q{sub CDW1} {approx} 0.70(0)c* is in good agreement with the expected value. A second, smaller {Delta}{sub 2} = 50 meV gap is due to a second CDW with a* - q{sub CDW2} {approx} 0.68(5)a*. The… more

Date: February 15, 2010

Creator: Moore, R. G.; /SLAC, SSRL /Stanford U., Geballe Lab.; Brouet, V.; /Orsay, LPS; He, R.; /SLAC, SSRL /Stanford U., Geballe Lab. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Field-induced Gap and Quantized Charge Pumping in Nano-helix

We propose several novel physical phenomena based on nano-scale helical wires. Applying a static electric field transverse to the helical wire induces a metal to insulator transition, with the band gap determined by the applied voltage. Similar idea can be applied to 'geometrically' constructing one-dimensional systems with arbitrary external potential. With a quadrupolar electrode configuration, the electric field could rotate in the transverse plane, leading to a quantized dc charge current p… more

Date: February 15, 2010

Creator: Qi, Xiao-Liang; /Stanford U., Phys. Dept. /Tsinghua U., Beijing; Zhang, Shou-Cheng & /Stanford U., Phys. Dept.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Material and Doping Dependence of the Nodal and Anti-Nodal Dispersion Renormalizations in Single- and Multi-Layer Cuprates

In this paper we present a review of bosonic renormalization effects on electronic carriers observed from angle-resolved photoemission spectra in the cuprates. Specifically, we discuss the viewpoint that these renormalizations represent coupling of the electrons to the lattice and review how materials dependence, such as the number of CuO{sub 2} layers, and doping dependence can be understood straightforwardly in terms of several aspects of electron-phonon coupling in layered correlated materia… more

Date: February 15, 2010

Creator: Johnston, S.; /SLAC, /Waterloo U.; Lee, W. S.; /Stanford U., Geballe Lab. /SLAC; Nowadnick, E. A.; /SLAC /Stanford U., Phys. Dept. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Multiple charge density wave transitions in Gd2Te5

Diffraction measurements performed via transmission electron microscopy and high resolution X-ray scattering reveal two distinct charge density wave transitions in Gd{sub 2}Te{sub 5} at T{sub c1} = 410(3) and T{sub c2} = 532(3) K, associated with the on-axis incommensurate lattice modulation and off-axis commensurate lattice modulation respectively. Analysis of the temperature dependence of the order parameters indicates a non-vanishing coupling between these two distinct CDW states.

Date: February 15, 2010

Creator: Shin, K. Y.; Ru, N.; Condron, C. L.; Wu, Y. Q.; Kramer, M. J.; Toney, M. F. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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NLO Jet Physics with BlackHat

We present several results obtained using the BLACKHAT next-to-leading order QCD program library, in conjunction with SHERPA. In particular, we present distributions for vector boson plus 1,2,3-jet production at the Tevatron and at the asymptotic running energy of the Large Hadron Collider, including new Z + 3-jet distributions. The Z + 2-jet predictions for the second-jet P{sub T} distribution are compared to CDF data. We present the jet-emission probability at NLO in W + 2-jet events at the L… more

Date: February 15, 2010

Creator: Berger, C. F.; Bern, Z.; Dixon, L. J.; Cordero, F. Febres; Forde, D.; Gleisberg, T. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Optical properties of the Ce and La ditelluride charge density wave compounds

The La and Ce di-tellurides LaTe{sub 2} and CeTe{sub 2} are deep in the charge-density-wave (CDW) ground state even at 300 K. We have collected their electrodynamic response over a broad spectral range from the far infrared up to the ultraviolet. We establish the energy scale of the single particle excitation across the CDW gap. Moreover, we find that the CDW collective state gaps a very large portion of the Fermi surface. Similarly to the related rare earth tri-tellurides, we envisage that int… more

Date: February 15, 2010

Creator: Lavagnini, M.; Sacchetti, A.; Degiorgi, L.; Shin, K. Y. & Fisher, I. R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Optical Properties of the Charge-Density-Wave Polychalcogenide Compounds R2Te5 (R=Nd, Sm and Gd)

We investigate the rare-earth polychalcogenide R{sub 2}Te{sub 5} (R = Nd, Sm and Gd) charge-density-wave (CDW) compounds by optical methods. From the absorption spectrum we extract the excitation energy of the CDW gap and estimate the fraction of the Fermi surface which is gapped by the formation of the CDW condensate. In analogy to previous findings on the related RTe{sub n} (n = 2 and 3) families, we establish the progressive closing of the CDW gap and the moderate enhancement of the metallic… more

Date: February 15, 2010

Creator: Pfuner, F.; Degiorgi, L.; /Zurich, ETH; Shin, K.Y.; Fisher, I.R. & /Stanford U., Geballe Lab.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Outflow Feedback Regulated Massive Star Formation in Parsec-Scale Cluster Forming Clumps

We investigate massive star formation in turbulent, magnetized, parsec-scale clumps of molecular clouds including protostellar outflow feedback using three dimensional numerical simulations of effective resolution 2048{sup 3}. The calculations are carried out using a block structured adaptive mesh refinement code that solves the ideal MHD equations including self-gravity and implements accreting sink particles. We find that, in the absence of regulation by magnetic fields and outflow feedback, … more

Date: February 15, 2010

Creator: Wang, Peng; /KIPAC, Menlo Park /Stanford U., Phys.Dept.; Li, Zhi-Yun; /Virginia U., Astron. Dept.; Abel, Tom; /KIPAC, Menlo Park /Stanford U., Phys.Dept. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Phases of Augmented Hadronic Light-Front Wave Functions

It is an important question whether the final/initial state gluonic interactions which lead to naive-time-reversal-odd single-spin asymmetries and diffraction at leading twist can be associated in a definite way with the light-front wave function hadronic eigensolutions of QCD. We use light-front time-ordered perturbation theory to obtain augmented light-front wave functions which contain an imaginary phase which depends on the choice of advanced or retarded boundary condition for the gauge pot… more

Date: February 15, 2010

Creator: Brodsky, Stanley J.; Pasquini, Barbara; Xiao, Bo-Wen & Yuan, Feng

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Pressure induced Superconductivity in the Charge Density Wave Compound Tritelluride

A series of high-pressure electrical resistivity measurements on single crystals of TbTe{sub 3} reveal a complex phase diagram involving the interplay of superconducting, antiferromagnetic and charge density wave order. The onset of superconductivity reaches a maximum of almost 4 K (onset) near {approx} 12.4 GPa.

Date: February 15, 2010

Creator: Hamlin, J.J.; Zocco, D. A.; Sayles, T. A.; Maple, M. B.; Chu, J.-H.; Fisher, I.R. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Semiclassical Time Evolution of the Holes from Luttinger Hamiltonian

We study the semi-classical motion of holes by exact numerical solution of the Luttinger model. The trajectories obtained for the heavy and light holes agree well with the higher order corrections to the abelian and the non-abelian adiabatic theories in Ref. [1] [S. Murakami et al., Science 301, 1378 (2003)], respectively. It is found that the hole trajectories contain rapid oscillations reminiscent of the 'Zitterbewegung' of relativistic electrons. We also comment on the non-conservation of he… more

Date: February 15, 2010

Creator: Jiang, Z. F.; Li, R. D.; Zhang, Shou-Cheng & Liu, W. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Simulation of the Focusing DIRC Optics with Mathematica

The Focusing DIRC is considered for the Barrel PID at a possible Super-B factory. To reduce sensitivity to background, it would be desirable to reduce a size of the present BaBar photon detector. One way to do it is to replace it with a focusing optics and use smaller photon detector pixels. We have simulated the focusing optics with simulation software based on a 3D calculation performed with the Mathematica program. The software does not use Optica package, instead, it uses its own 3D algorit… more

Date: February 15, 2010

Creator: Va'vra, J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Single-particle and collective mode couplings associated with 1- and 2-directional electronic ordering in metallic RTe3 (R = Ho, Dy, Tb)

The coupling of phonons with collective modes and single-particle gap excitations associated with one (1d) and two-directional (2d) electronically-driven charge-density wave (CDW) ordering in metallic RTe{sub 3} is investigated as a function of rare-earth ion chemical pressure (R = Tb, Dy, Ho) using femtosecond pump-probe spectroscopy. From the T-dependence of the CDW gap {Delta}{sub CDW} and the amplitude mode (AM) we find that while the transition to a 1d-CDW ordered state at Tc1 initially pr… more

Date: February 15, 2010

Creator: Yusupov, R. V.; Mertelj, T.; Chu, J.-H.; Fisher, I. R. & Mihailovic, D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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STM Studies of TbTe3: Evidence for a Fully Incommensurate Charge Density Wave

We observe unidirectional charge density wave ordering on the cleaved surface of TbTe{sub 3} with a Scanning Tunneling Microscope at {approx}6 K. The modulation wave-vector q{sub CDW} as determined by Fourier analysis is 0.71 {+-} 0.02 x2{pi}/c. Where c is one edge of the in-plane 3D unit cell. Images at different tip-sample voltages show the unit cell doubling effects of dimerization and the layer below. Our results agree with bulk X-ray measurements, with the addition of (1/3) x2{pi}/a orderi… more

Date: February 15, 2010

Creator: Fang, A.; Ru, N.; Fisher, I.R.; /Stanford U., Appl. Phys. Dept.; Kapitulnik, A. & /Stanford U., Appl. Phys. Dept. /Stanford U., Phys. Dept.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Time-Resolved Photoemission of Correlated Electrons Driven Out of Equilibrium

We describe the temporal evolution of the time-resolved photoemission response of the spinless Falicov-Kimball model driven out of equilibrium by strong, applied fields. The model is one of the few possessing a metal-insulator transition and admitting an exact solution in the time domain. The nonequilibrium dynamics, evaluated using an extension of dynamical mean-field theory, show how the driven system differs from two common viewpoints - a quasi-equilibrium system at an elevated, effective te… more

Date: February 15, 2010

Creator: Moritz, B.; /SLAC, SIMES; Devereaux, T.P.; /SLAC, SIMES /Stanford U., Geballe Lab.; Freericks, J.K. & U., /Georgetown

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Unraveling L_{n,k}: Grassmannian Kinematics

It was recently proposed that the leading singularities of the S-Matrix of N = 4 super Yang-Mills theory arise as the residues of a contour integral over a Grassmannian manifold, with space-time locality encoded through residue theorems generalizing Cauchy's theorem to more than one variable. We provide a method to identify the residue corresponding to any leading singularity, and we carry this out explicitly for all leading singularities at tree level and one-loop. We also give several example… more

Date: February 15, 2010

Creator: Kaplan, Jared

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Impedance Scaling for Small-angle Tapers and Collimators

In this note I will prove that the impedance calculated for a small-angle collimator or taper, of arbitrary 3D profile, has a scaling property that can greatly simplify numerical calculations. This proof is based on the parabolic equation approach to solving Maxwell's equation developed in Refs. [1, 2]. We start from the parabolic equation formulated in [3]. As discussed in [1], in general case this equation is valid for frequencies {omega} >> c/a where a is a characteristic dimension of … more

Date: February 11, 2010

Creator: Stupakov, G.

Item Type: Report

Partner: UNT Libraries Government Documents Department