The Higgs as a Portal to Plasmon-like Unparticle Excitations

A renormalizable coupling between the Higgs and a scalar unparticle operator O_U of non-integer dimension d_U<2 triggers, after electroweak symmetry breaking, an infrared divergent vacuum expectation value for O_U. Such IR divergence should be tamed before any phenomenological implications of the Higgs-unparticle interplay can be drawn. In this paper we present a novel mechanism to cure that IR divergence through (scale-invariant) unparticle self-interactions, which has properties qualitatively different from the mechanism considered previously. Besides finding a mass gap in the unparticle continuum we also find an unparticle pole reminiscent of a plasmon resonance. Such unparticle features could be explored experimentally through their mixing with the Higgs boson.Comment: 12 LaTeX pages, 2 figure

Donor-photoluminescence Line Shapes From Gaas-(ga,al)as Quantum Wells

The D°-h impurity-related photoluminescence spectra of confined donors in GaAs-(Ga,Al)As quantum wells is theoretically investigated within the effective-mass approximation. The impurity wave functions and binding energies are evaluated via a variational procedure. Calculations are performed for different well widths, temperatures, and impurity doping profiles. Typical D-h theoretical photoluminescence line shapes show peaked structures corresponding to on-center and on-edge donors in good agreement with experimental results. © 1993 The American Physical Society.4742406240

Momentum conservation and local field corrections for the response of interacting Fermi gases

We reanalyze the recently derived response function for interacting systems in relaxation time approximation respecting density, momentum and energy conservation. We find that momentum conservation leads exactly to the local field corrections for both cases respecting only density conservation and respecting density and energy conservation. This rewriting simplifies the former formulae dramatically. We discuss the small wave vector expansion and find that the response function shows a high frequency dependence of $\omega^{-5}$ which allows to fulfill higher order sum rules. The momentum conservation also resolves a puzzle about the conductivity which should only be finite in multicomponent systems

Resonant thermal transport in semiconductor barrier structures

I report that thermal single-barrier (TSB) and thermal double-barrier (TDB) structures (formed, for example, by inserting one or two regions of a few Ge monolayers in Si) provide both a suppression of the phonon transport as well as a resonant-thermal-transport effect. I show that high-frequency phonons can experience a traditional double-barrier resonant tunneling in the TDB structures while the formation of Fabry-Perot resonances (at lower frequencies) causes quantum oscillations in the temperature variation of both the TSB and TDB thermal conductances $\sigma_{\text{TSB}}$ and $\sigma_{\text{TDB}}$.Comment: 4 pages. 4 figure.

Thermoelectrics Near the Mott Localization-Delocalization Transition

We give an overview on current status of the theoretical research on Thermoelectricity for correlated materials. We derive the theoretical formulas which become exact at low and high temperature and discuss the intermediate temperature results. In particular, we show that within Dynamical Mean Field Theory the low temperature sign of the thermopower is not necessary the same as in LDA, and that significant non-universality is expected due to strong correlations.Comment: appeared in "Properties and Applications of Thermoelectric Materials", Edited by V. Zlatic and A.C. Hewson, Springe

Metal-insulator transition in Ca_{1-x}Li_xPd_3O_4

Metal-insulator transition in Ca_{1-x}Li_xPd_3O_4 has been studied through charge transport measurements. The resistivity, the Seebeck coefficient, and the Hall coefficient are consistently explained in terms of a simple one-band picture, where a hole with a moderately enhanced mass is itinerant three-dimensionally. Contrary to the theoretical prediction [Phys. Rev. B62, 13426 (2000)], CaPd_3O_4 is unlikely to be an excitonic insulator, and holds a finite carrier concentration down to 4.2 K. Thus the metal-insulator transition in this system is basically driven by localization effects.Comment: RevTeX4 format, 4 pages, 5 eps figure

Optimizing thermal transport in the Falicov-Kimball model: binary-alloy picture

We analyze the thermal transport properties of the Falicov-Kimball model concentrating on locating regions of parameter space where the thermoelectric figure-of-merit ZT is large. We focus on high temperature for power generation applications and low temperature for cooling applications. We constrain the static particles (ions) to have a fixed concentration, and vary the conduction electron concentration as in the binary-alloy picture of the Falicov-Kimball model. We find a large region of parameter space with ZT>1 at high temperature and we find a small region of parameter space with ZT>1 at low temperature for correlated systems, but we believe inclusion of the lattice thermal conductivity will greatly reduce the low-temperature figure-of-merit.Comment: 13 pages, 14 figures, typeset with ReVTe

Heat transport of electron-doped Cobaltates

Within the t-J model, the heat transport of electron-doped cobaltates is studied based on the fermion-spin theory. It is shown that the temperature dependent thermal conductivity is characterized by the low temperature peak located at a finite temperature. The thermal conductivity increases monotonously with increasing temperature at low temperatures T $<$ 0.1$J$, and then decreases with increasing temperature for higher temperatures T $>$ 0.1$J$, in qualitative agreement with experimental result observed from Na$_{x}$CoO$_{2}$ .Comment: 4 pages, 1 fig, corrected typos, accepted for publication in Commun. Theor. Phy

Auxiliary particle theory of threshold singularities in photoemission and X-ray absorption spectra: Test of a conserving T-matrix approximation

We calculate the exponents of the threshold singularities in the photoemission spectrum of a deep core hole and its X-ray absorption spectrum in the framework of a systematic many-body theory of slave bosons and pseudofermions (for the empty and occupied core level). In this representation, photoemission and X-ray absorption can be understood on the same footing; no distinction between orthogonality catastrophe and excitonic effects is necessary. We apply the conserving slave particle T-matrix approximation (CTMA), recently developed to describe both Fermi and non-Fermi liquid behavior systems with strong local correlations, to the X-ray problem as a test case. The numerical results for both photoemission and X-ray absorption are found to be in agreement with the exact infrared powerlaw behavior in the weak as well as in the strong coupling regions. We point out a close relation of the CTMA with the parquet equation approach of Nozi{\`e}res et al.Comment: 10 pages, 9 figures, published versio

Coherent Control for a Two-level System Coupled to Phonons

The interband polarizations induced by two phase-locked pulses in a semiconductor show strong interference effects depending on the time tau_1 separating the pulses. The four-wave mixing signal diffracted from a third pulse delayed by tau is coherently controlled by tuning tau_1. The four-wave mixing response is evaluated exactly for a two-level system coupled to a single LO phonon. In the weak coupling regime it shows oscillations with the phonon frequency which turn into sharp peaks at multiples of the phonon period for a larger coupling strength. Destructive interferences between the two phase-locked pulses produce a splitting of the phonon peaks into a doublet. For fixed tau but varying tau_1 the signal shows rapid oscillations at the interband-transition frequency, whose amplitude exhibits bursts at multiples of the phonon period.Comment: 4 pages, 4 figures, RevTex, content change