Temperature Dependence Of Brillouin Light Scattering Spectra Of Acoustic Phonons In Silicon

Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons. (C) 2015 AIP Publishing LLC.National Science Foundation (NSF) Thermal Transport Processes Program CBET-1336968PhysicsCenter for Complex Quantum SystemsMaterials Science and EngineeringTexas Materials InstituteMechanical Engineerin

Reduction of the QCD string to a time component vector potential

We demonstrate the equivalence of the relativistic flux tube model of mesons to a simple potential model in the regime of large radial excitation. We make no restriction on the quark masses; either quark may have a zero or finite mass. Our primary result shows that for fixed angular momentum and large radial excitation, the flux tube/QCD string meson with a short-range Coulomb interaction is described by a spinless Salpeter equation with a time component vector potential V(r) = ar - k/r.Comment: RevTeX4, 10 pages, 3 eps figure

Long-wavelength spin- and spin-isospin correlations in nucleon matter

We analyse the long-wavelength response of a normal Fermi liquid using Landau theory. We consider contributions from intermediate states containing one additional quasiparticle-quasihole pair as well as those from states containing two or more additional quasiparticle-quasihole pairs. For the response of an operator corresponding to a conserved quantity, we show that the behavior of matrix elements to states with more than one additional quasiparticle-quasihole pair at low excitation energies $\omega$ varies as $1/\omega$. It is shown how rates of processes involving transitions to two quasiparticle-quasihole states may be calculated in terms of the collision integral in the Landau transport equation for quasiparticles.Comment: 10 pages, 3 figure

Scanning tunneling microscopy and spectroscopy of sodium-chloride overlayers on the stepped Cu(311) surface: Experimental and theoretical study

The physical properties of ultrathin NaCl overlayers on the stepped Cu(311) surface have been characterized using scanning tunneling microscopy (STM) and spectroscopy, and density functional calculations. Simulations of STM images and differential conductance spectrum were based on the Tersoff-Hamann approximation for tunneling with corrections for the modified tunneling barrier at larger voltages and calculated Kohn-Sham states. Characteristic features observed in the STM images can be directly related to calculated electronic and geometric properties of the overlayers. The measured apparent barrier heights for the mono-, bi-, and trilayers of NaCl and the corresponding adsorption-induced changes in the work function, as obtained from the distance dependence of the tunneling current, are well reproduced by and understood from the calculated results. The measurements revealed a large reduction of the tunneling conductance in a wide voltage region, resembling a band gap. However, the simulated spectrum showed that only the onset at positive sample voltages may be viewed as a valence band edge, whereas the onset at negative voltages is caused by the drastic effect of the electric field from the tip on the tunneling barrier

Static response of Fermi liquids with tensor interactions

We use Landau's theory of a normal Fermi liquid to derive expressions for the static response of a system with a general tensor interaction that conserves the total spin and the total angular momentum of the quasiparticle-quasihole pair. The magnetic susceptibility is calculated in detail, with the inclusion of the center of mass tensor and cross vector terms in addition to the exchange tensor one. We also introduce a new parametrization of the tensor Landau parameters which significantly reduces the importance of high angular harmonic contributions. For nuclear matter and neutron matter we find that the two most important effects of the tensor interaction are to give a contribution from multipair states and to renormalize the magnetic moments. Response to a weak probe may be calculated using similar methods, replacing the magnetic moments with the matrix elements of the weak charges

Analytic Quantization of the QCD String

We perform an analytic semi-classical quantization of the straight QCD string with one end fixed and a massless quark on the other, in the limits of orbital and radial dominant motion. We compare our results to the exact numerical semi-classical quantization. We observe that the numerical semi-classical quantization agrees well with our exact numerical canonical quantization.Comment: RevTeX, 10 pages, 9 figure

Universal light quark mass dependence and heavy-light meson spectroscopy

Clean predictions are presented for all the spin-averaged heavy-light meson spectroscopies. A new symmetry is identified wherein the energy eigenstates have a universal dependence on both the light and heavy quark masses. This universality is used in an efficient analysis of these mesons within the QCD string/flux tube picture. Unique predictions for all the D, D_s, B, and B_s type mesons in terms of just four measured quantities.Comment: REVTeX4, 6 pages, 9 eps figure

Semi-leptonic B decays into higher charmed resonances

We apply HQET to semi-leptonic $B$ meson decays into a variety of excited charm states. Using three realistic meson models with fermionic light degrees of freedom, we examine the extent that the sum of exclusive single charmed states account for the inclusive semi-leptonic $B$ decay rate. The consistency of form factors with the Bjorken and Voloshin sum rules is also investigated.Comment: Latex, 27 pages. A few references and errors corrected, to appear in Phys. Rev.