Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session X37: Semiconductors IV: Electronic and Optical Properties II |
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Sponsoring Units: FIAP Chair: Udo Pernisz, Dow Corning Corp. Room: Morial Convention Center 229 |
Friday, March 14, 2008 8:00AM - 8:12AM |
X37.00001: Electronic Structure of Silicon Phases Resulting from Decompression from $\beta$-Sn Brad Malone, Jay Sau, Marvin Cohen We present an \textit{ab initio} study of the electronic structure of the silicon phases that result from decompression from the metallic $\beta$-Sn phase, namely the BC8 (Si III), the hexagonal diamond (Si IV), the R8 (Si XII), and the yet unobserved ST12 phases. To correct for the inadequacies in the DFT-LDA quasiparticle energy spectra we employ quasiparticle corrections with the framework of the GW approximation. In doing so we find that the R8 phase should be semiconducting at lower pressures We also analyze the effect of strain and doping on these materials in an attempt to find novel applications for these phases, from high-mobility semiconductors to superconductivity. [Preview Abstract] |
Friday, March 14, 2008 8:12AM - 8:24AM |
X37.00002: First principles calculations of optical and x-ray spectra from atomic coordinates alone J.J. Kas, M. Prange, F.D. Vila, Y. Takimoto, J.J. Rehr Theoretical calculations of various x-ray and optical spectroscopies often rely on semi-empirical or phenomenological models to account for many-body effects and thermal vibrations. Typically such models include a number of parameters which complicate fitting schemes that extract physical quantities from experimental spectra. Here we present an approach for {\it {ab initio} } calculations of these spectra starting from structure alone. A many-pole model of the dielectric function is introduced to calculate the self-energy and spectral function,\footnote{J. J. Kas et al., Phys. Rev. B {\bf76} 195116 (2007).} while a density functional theory calculation of the dynamical matrix is used to calculate effects of thermal vibrations. \footnote{Fernando D. Vila et al., Phys. Rev. B {\bf 76}, 014301 (2007).} In addition, core-hole effects are incorporated with RPA screening. \footnote{A. L. Ankudinov et al., Phys. Rev. B {\bf 71}, 165110 (2005).} This approach has been incorporated into FEFF9, a new version of the real-space multiple-scattering FEFF code for broad spectrum calculations of various optical and x-ray spectra. [Preview Abstract] |
Friday, March 14, 2008 8:24AM - 8:36AM |
X37.00003: Surface states of the Topological Insulator Bi$_{1-x}$ Sb$_x$ Jeffrey Teo, Liang Fu, Charles Kane The alloy Bi$_{1-x}$Sb$_x$ is a narrow gap semiconductor for
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Friday, March 14, 2008 8:36AM - 8:48AM |
X37.00004: Optical, Electronic and Structural Properties of Y$_{x}$Sc$_{1-x}$N Robert Bruce vanDover, John Gregoire, Steve Kirby Semiconducting Y$_{x}$Sc$_{1-x}$N thin films are reactively sputtered onto a variety of surfaces, resulting in films varying from nanocrystalline to epitaxial (single crystalline). As a function of composition, we investigate the variations in the crystalline lattice, Hall mobility, absorptivity and direct and indirect band gaps. We find this material to be a solid solution semiconductor across the entire composition range. The tunable band gap and high absorptivity of this semiconductor make it an interesting photovoltaic material. Details on this application will be presented as well as prospects of this material's use as the host for ferromagnetic transition metals. [Preview Abstract] |
Friday, March 14, 2008 8:48AM - 9:00AM |
X37.00005: Free-electron induced mode mixing and surface-polariton enhanced reflected THz-field Danhong Huang, Godfrey Gumbs, Plau Alsing, Dave Cardimona The main result of this talk is the prediction of large enhancements at the band edges of a coupled Bloch-surface-plasmon-polariton band in the spectrum of the reflected far electromagnetic field due to anti-crossing gaps induced by the strong coupling between the continuous surface-plasmon-polariton mode and the discrete Bloch-like modes. The existence of these Bloch-like modes is a direct consequence of the nonlocal mixing of specular and diffraction modes of the reflected electromagnetic field by free-electron induced optical polarization and the interference of a pair of surface optical-polarization waves with opposite Bragg order numbers in the presence of a grating. The interference of these two counter-propagating surface waves leads to the formation of a Wannier-like state with associated electromagnetic fields localized within the grating-gap regions. The effects of the sheet density, grating period and absorption loss on the optical enhancements of both transmitted and reflected electromagnetic fields are investigated. [Preview Abstract] |
Friday, March 14, 2008 9:00AM - 9:12AM |
X37.00006: Absorption and Photoluminescence Analysis of InAs/GaSb Superlattices Exhibiting Lateral Composition Modulation Julia Wickett, Jianhua Li, Donna Stokes The effects of lateral composition modulation (LCM) in (InAs)$_{13}$/(GaSb)$_{13}$ superlattices on the structure and optical response of the material have been investigated by double crystal x-ray diffraction (XRD), infrared absorption and photoluminescence (PL). Superlattices (SL) were grown by molecular beam epitaxy (MBE) on GaSb (001) substrates with InSb interfacial bonds. Various buffer/substrate combinations were employed to determine if strain manipulation could be used to improve the optical response of the system. Modeling of XRD data has been used to determine the strain state of the SL layers with respect to the growth template. Absorption and PL measurements indicate that strain significantly affects the optical responses of the samples and manipulation and control over the strain state of the system will be key in employing LCM superlattices for optical applications. [Preview Abstract] |
Friday, March 14, 2008 9:12AM - 9:24AM |
X37.00007: Probing ErAs nanoparticle density of states using capacitance-voltage Kasey Russell, Venkatesh Narayanamurti, Joshua Zide, Arthur Gossard Two asymmetric In$_{0.53}$Ga$_{0.47}$As/In$_{0.53}$Al$_{0.47}$As double-barrier samples are fabricated and compared using low-temperature capacitance-voltage measurements. The two samples are identical except for a layer of ErAs nanoparticles embedded within the quantum well layer of one of the samples. A clear difference in the capacitance-voltage profile is observed between the two samples, and the difference is attributed to additional available states associated with the ErAs nanoparticles. These results are compared with a charge-step simulation of the low-frequency capacitance of the device in order to estimate the density of states contributed by the ErAs nanoparticles. [Preview Abstract] |
Friday, March 14, 2008 9:24AM - 9:36AM |
X37.00008: Photon-like plasmon polariton in a nanocoaxial waveguide Yun Peng, Xiwen Wang, Krzysztof Kempa We study propagation of electromagnetic waves in a nano-coaxial waveguide for frequencies below the surface plasmon frequency. We show, that for sufficently low frequencies, the waveguide supports a plasmon polariton mode that resembles, and indeed reduces to the conventional TEM mode of the conventional coax, known in the radiotechnology. We consider also coupling of this mode to the external radiation, and show that it can be made very efficient with appropriate antenna-like arrangements. [Preview Abstract] |
Friday, March 14, 2008 9:36AM - 9:48AM |
X37.00009: X-ray Absorption Study of Amorphous Metal Semiconductor Alloys $M_x Si_{1-x} $ (M: Gd,Y) Near the Metal Insulator Transition Erik Helgren, F. Hellman, Li Zeng, J.W. Freeland, P. Ryan, D. Haskel, R. Winarski, M. van Veenendaal, R. Wu X-ray absorption structure (XAS) at both Si K edges and Gd M edges were measured at compositions close to the metal insulator transition (MIT) for amorphous $Gd_x Si_{1-x} $ (x = 0.11 - 0.21) and $Y_x Si_{1-x} $ (x=0.13) from 10-300K. Spectral lineshape is unchanged as a function of composition, despite the presence of the MIT at x = 0.14. Comparison with calculations indicates that Gd is in the 3+ state for all compositions and temperatures measured. An anomalous temperature dependent absorption is seen below approximately 70K; the energies of the absorption peaks are unaffected, indicating no change in valence, but the absolute magnitude of absorption is temperature dependent for both K and M edges, up to 40 eV from the edges. This temperature dependence is related to changes in the nature of the conduction band states, specifically a transfer of weight from Si p-states to more localized Gd p-states. However similar shifts in the magnitude of the Si K edge are found in the non-magnetic analog system $Y_x Si_{1-x} $. Thus this transfer cannot be solely related to the magnetically-dependent localization phenomena previously observed in $Gd_x Si_{1-x} $, and we argue that it is related to electronic correlation effects present in both systems. [Preview Abstract] |
Friday, March 14, 2008 9:48AM - 10:00AM |
X37.00010: Eu L3-edge Resonant Inelastic X-ray Scattering on EuB6 Jungho Kim, D. Ellis, B.K. Cho, E.J. Choi, A. Said, Y. Shvydko, Young-June Kim We present the frst Eu L$_{3}$-edge resonant inelastic x-ray scattering (RIXS) spectra on the cubic EuB$_{6}$ using vertical and horizontal scattering geometries. EuB$_{6}$ is an undistorted cubic compound being free from complications like lattice distortion. The valence of Eu is 2$^{+}$ (4$f^{7})$. Electronic states near the Fermi edge are formed by the hybridization of Eu 5$d_{x2-y2 }$and B 2$p$. According to optical spectroscopy studies, a number of excitations exist over a wide energy range up to 40 eV. In particular, optical spectrum below 10 eV consists of a number of narrow strong peaks. These peaks were assigned to 2$p$-5$d$ charge transfer or 4$f$-5$d$ on-site excitations. In the current Eu L$_{3}$-edge RIXS experiment, we found that resonant enhancements occur both near and above the Eu L$_{3}$ absorption peak. In both resonance features, we identify a number of narrow energy loss features and compare those features with the optical spectroscopy spectrum. Interestingly, we observed a drastic dependence on measurement geometry in a resonant enhancement above the Eu L3 absorption peak. We discuss the excitation symmetry based on the geometry dependence. This study demonstrates the utility of the rare-earth L$_{3}$-edge RIXS as a probe of excited states in rare-earth systems. [Preview Abstract] |
Friday, March 14, 2008 10:00AM - 10:12AM |
X37.00011: Effect of Dielectric Response on the Magic Angle Mystery in EELS Adam Sorini, John Rehr, Zachary Levine The ``magic'' collection angle in electron energy-loss spectroscopy (EELS) is that angle at which the spectra from an anisotropic sample ``magically'' becomes orientation independent. The ``myster''" is that non-relativistic theory predicts a magic angle typically a factor of two too large in modern EELS experiments. Recently it has been shown that a relativistic treatment largely explains the discrepancy [1]. Here, we suggest that the dielectric response of the sample can lead to still larger magic angle corrections for low energy-loss spectra [2]. These dielectric effects are included in a relativistic, independent particle theory using the generalized Lorentz gauge. The effect is illustrated by a calculation of the magic angle including both relativistic and first principles dielectric corrections for graphite and for boron nitride. \newline [1] P. Schattschneider, C. Hebert, H. Franco, and B. Jouffrey, Phys. Rev. B, 72, 045142 (2005) \newline [2] A. P. Sorini, J. J. Rehr, and Z. H. Levine (UW Preprint, Nov. 2007) [Preview Abstract] |
Friday, March 14, 2008 10:12AM - 10:24AM |
X37.00012: Wave-front engineering by Huygens-Fresnel principle for nonlinear optical interactions in domain engineered structures Zhu Yongyuan The wave-front engineering for nonlinear optical interactions was discussed. Using Huygens-Fresnel principle we developed a general theory and technique for domain engineering with conventional quasi-phase-matching (QPM) structures being the special cases. We put forward the concept of local QPM, which suggests that the QPM is fulfilled only locally not globally. Experiments agreed well with the theoretical prediction. The proposed scheme integrates three optical functions: generating, focusing and beam splitting of second-harmonic wave, thus making the device more compact. This work was supported by the State Key Program for Basic Research of China (Grant No. 2004CB619003) and also by the NNSF of China (Grant Nos.10523001, 10504013 and 10674065). [Preview Abstract] |
Friday, March 14, 2008 10:24AM - 10:36AM |
X37.00013: Influence of Phonon dimensionality on Electron Energy Relaxation Ilari Maasilta, Jenni Karvonen We studied experimentally the role of phonon dimensionality on electron-phonon (e-p) interaction in thin copper wires evaporated either on suspended silicon nitride membranes or on bulk substrates, at sub-Kelvin temperatures. The power emitted from electrons to phonons was measured using sensitive normal metal-insulator-superconductor (NIS) tunnel junction thermometers. Membrane thicknesses ranging from 30 nm to 750 nm were used to clearly see the onset of the effects of two-dimensional (2D) phonon system. We observed for the first time that a 2D phonon spectrum clearly changes the temperature dependence and strength of the e-p scattering rate, with the interaction becoming stronger at the lowest temperatures below $\sim$ 0.5 K for the 30 nm membranes\footnote{J. T. Karvonen and I. J. Maasilta, Phys. Rev. Lett. {\bf 99}, 145503 (2007).}. [Preview Abstract] |
Friday, March 14, 2008 10:36AM - 10:48AM |
X37.00014: Hartree-Fock-Cluster Investigation of Nuclear Quadrupole Interactions in Solid Chalcogens, Selenium and Tellurium. M.M. Aryal, N.B. Maharjan, D.D. Paudyal, D.R. Mishra, S.R. Byahut, R.H. Scheicher, S.R. Badu, J. Jeong, Lee Chow, T.P. Das Using the first-principles Hartree-Fock Cluster Procedure, we have studied the electronic structures of pure chain like Selenium and Tellurium, pure ring structured Selenium, Tellurium impurity in chain and ring-structured Selenium and Selenium impurity in chain-structured Tellurium chain. For our investigations in all the systems we have carried out convergence studies with respect to variational basis set sizes,sizes of clusters and electron correlation effects using many-body perturbation theory. Using our calculated electronic field-gradient parameters q in the pure chain systems and employing the experimental quadrupole coupling constants (e$^{2}$qQ), the values Q($^{77}$Se)=(0.50$\pm $0.04) 10$^{-28}$ m$^{2}$ and Q($^{125}$Te)=-(0.2$\pm $0.02) 10$^{-28}$m$^{2}$. Results will also be presented for the asymmetry parameters $\eta $ for the pure chain systems and the e$^{2}$qQ and $\eta $ for $^{77}$Se in selenium ring. Our calculated values for e$^{2}$qQ and $\eta $ for the impurity systems will also be presented and compared with available experimental data and earlier theoretical results. [Preview Abstract] |
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