UScholar Works
 
Filters: School Or College: "College of Science" Department: "Physics" Collection: "ir_uspace"
226 - 250 of 924
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CreatorTitleDescriptionSubjectDate
226 Mattis, Daniel C.Exactly soluble model of interacting electronsWe diagonalize a many-fermion Hamiltonian consisting of terms quadratic as well as quartic in the field operators. A dual spectrum of eigenstates is an interesting result. We also derive a formula for obtaining the free energy at finite temperature.Eigenstates; Free energy; Excitation spectrum1972
227 Mattis, Daniel C.Exactly solvable model of a magnetic impurityA slight modification of the "mixing" term in Anderson's model of a magnetic impurity produces an exactly solvable model. Results of some preliminary calculations are given, and upper and lower bounds on Anderson's model are obtained by means of the exact solutions. .Magnetic impurity; Ground-state energy; Free energy1971-11
228 Symko, Orest GeorgeExchange interactions and magnetic dimension in Cu(L-alanine)2A study of the magnetic properties of the copper (II) complex of the amino acid L-alanine [CU(Lalanine) 2] is reported. The susceptibility of a powder sample has been measured between 0.013 and 240 K. A linear-spin-chain model with antiferromagnetic exchange coupling J = -0.52 K fits well the susce...Cu(L-alanine)2; Exchange interactions; Magnetic dimension1991-01
229 Vardeny, Zeev Valentine; Ehrenfreund, Eitan A.Excitation dynamics in disubstituted polyacetyleneWe studied the excitation dynamics in films of disubstituted polyacetylene, a degenerate ground-state conjugated polymer, using psec transient and steady-state spectroscopies. The polymer is found to support charged and neutral topological soliton excitations concurrent with a strong intrinsic p...Excitation dynamics; Disubstituted polyacetylene; Laser action1999-05
230 Vardeny, Zeev ValentineExcitation dynamics in single molecular crystals of α-hexathiophene from femtosecond to millisecondWe identify odd- and even-parity states and measure transient photomodulation spectra of Frenkel excitons in a-hexathiophene single crystals. The lowest Frenkel excitons are characterized by a stimulated emission band at ~2 eV and an absorption band at 1.3 eV. Intramolecular internal conversion go...Excitation dynamics; alpha-hexathiophene; Frenkel excitons; pi-conjugated polymers; Photoexcitation2001-04
231 Vardeny, Zeev Valentine; Taylor, P. CraigExcitation energy dependence of photoinduced absorption in intrinsic a-Si:HWe have studied subgap absorption of intrinsic a-Si:H induced by below- and above-gap photoexcitation. We find very similar photoinduced subgap absorption spectra when excited with 2.4 eV or 1.2 eV light. Both spectra exhibit a power-law dependence on laser intensity ?T ~ 1a, where a is 0.5 and 0.7...Intrinsic a-Si:H; Subgap absorption; Photoinduced absorption; Gap photoexcitation; Photomodulation; Electronic states1998
232 Vardeny, Zeev Valentine; Raikh, Mikhail E.Excitations in opal photonic crystals infiltrated with polarizable mediaPhotonic crystals (PC) are a class of artificial structures with a periodic dielectric function. PCs can be a laboratory for testing fundamental processes involving interactions of radiation with matter in novel conditions. We have studied the optical properties of opal PCs that are infiltrated with...Opal photonic crystals; Polarizable media; Bragg gap; Polaritonic gap; Photonic stop band2002
233 Vardeny, Zeev Valentine; Raikh, Mikhail E.Excitations in photonic crystals infiltrated with polarizable mediaLight propagation in a photonic crystal with incomplete band gap, infiltrated with polarizable molecules is considered. We demonstrate that the interplay between the spatial dispersion caused by Bragg diffraction and polaritonic frequency dispersion gives rise to alternative propagating excitation...Polarizable media; Light propagation; Bragg diffraction; Excitations2001-06
234 DeTar, CarletonExcited states in staggered meson propagatorsWe report on preliminary results from multi-particle fits to meson propagators with three flavors of light dynamical quarks. We are able to measure excited states in propagators with pion quantum numbers, which we interpret as the pion 2S state, and argue is evidence of locality of the action. In t...Excited states; Meson propagators2004-03
235 Vardeny, Zeev ValentineExcited-state relaxation in ∏-conjugated polymersWe study ultrafast relaxation processes of odd- (Bu) and even-parity (Ag) exciton states in poly(p-phenylene vinylene) derivatives. The Bu states are studied using a regular two-beam pump-and-probe spectroscopy, which can monitor vibronic relaxation and exciton diffusion. In order to observe the A...Ultrafast relaxation; Excited-state relaxation; pi-conjugated polymers; PPV2002-05
236 Lupton, John MarkExciton confinement in organic dendrimer quantum wells for opto-electronic applicationsOrganic dendrimers are a fascinating new class of materials for opto-electronic applications. We present coupled electronic oscillator calculations on novel nanoscale conjugated dendrimers for use in organic light-emitting diodes. Strong confinement of excitations at the center of the dendrimers is ...Exciton confinement; Opto-electronic applications; Coupled electronic oscillator2002
237 Vardeny, Zeev ValentineExciton dynamics in single-walled nanotubes: transient photoinduced dichroism and polarized emissionUltrafast relaxation of photoexcitations in semiconducting single-walled carbon nanotubes (S-NTs) were investigated using polarized pump-probe photomodulation (with 150 fs time resolution) and cw polarized photoluminescence (PL). Both annealed and unannealed thin NT films and D2O solutions of isola...Exciton dynamics; Single-walled carbon nanotubes; SWNT; Transient photoinduced dichroism; Polarized emission; Ultrafast relaxation; Photoexcitations2005-03
238 Vardeny, Zeev ValentineExciton dynamics in soluble poly(p-phenylene vinylene)We report studies of poly(2,5-dioctyloxy paraphenylene vinylene) thin films and solutions by a variety of transient, steady state, and nonlinear optical techniques. The energy states and optical absorption of the dominant even and odd parity excitons have been determined. Photogenerated singlet exci...Exciton dynamics; Poly(p-phenylene vinylene); PPV; Pi-conjugated polymers1997
239 Vardeny, Zeev Valentine; Gellermann, WernerExciton dynamics in soluble poly(p-phenylene-vinylene): toward an ultrafast excitonic switchWe have applied a variety of ps transient and cw optical techniques to elucidate the dynamics, absorption, and emission properties of excitons in soluble derivatives of poly(p-phenylene vinylene) neat films and dilute solutions. We found that the photogenerated singlet excitons in both films and sol...Exciton dynamics; Excitonic switch1997-06
240 Lupton, John MarkExciton storage in CdSe/CdS tetrapod semiconductor nanocrystals: electric field effects on exciton and multiexciton statesCdSe/CdS nanocrystal tetrapods are interesting building blocks for excitonic circuits, where the flow of excitation energy is gated by an external stimulus. The physical morphology of the nanoparticle, along with the electronic structure, which favors electron delocalization between the two semicond...2012-01-01
241 Vardeny, Zeev ValentineExcitons in poly(para-phenylenevinylene)We show that one-electron band theory fails to describe optical absorption in PPV and the absorption spectrum can be described only within a Coulomb-correlated model. The lowest optical state is an exciton, whose binding energy is estimated theoretically to be 0.90 ± 0 . 1 5 e V Measurements of the...Poly(para-phenylenevinylene); PPV1994-11
242 Vardeny, Zeev ValentineExcitons, polarons, and laser action in poly(p-phenylene vinylene) filmsWe have used a multitude of linear and nonlinear cw optical spectroscopies to study the optical properties of water precursor poly(p-phenylene vinylene) (PPV) thin films. These spectroscopies include absorption, photoluminescence, photoinduced absorption and their respective optically detected magne...PPV films; Excitons; Laser action; Poly(p-phenylene vinylene)2003
243 Mattis, Daniel C.Existence of two phase transitions in Hubbard modelWe solve the Hubbard model, for one electron per atom in a simple cubic structure, using one-particle Green's functions. We determine the accuracy of this calculation to be good by comparison with an exact solution by Lieb and Wu of a one-dimensional limiting case.Critical temperature1969-12
244 DeTar, CarletonExotic hybrid mesons from improved Kogut-Susskind fermionsWe summarize our measurement of the mass of the exotic 1−+ hybrid meson using an improved Kogut-Susskind action. We show results from both quenched and dynamical quark simulations and compare with results from Wilson quarks. Extrapolation of these results to the physical quark mass allows compar...Chromomagnetic field; Kogut-Susskind fermions; Wilson quarks2003-05
245 DeTar, CarletonExotic hybrid mesons with light quarksHybrid mesons, made from a quark, an antiquark and gluons, can have quantum numbers inaccessible to conventional quark-antiquark states. Confirmation of such states would give information on the role of "dynamical" color in low energy QCD. We present preliminary results for hybrid meson masses using...Hybrid mesons; Kogut-Susskind quarks; Wilson quarks1997-02
246 DeTar, CarletonExotic meson spectroscopy from the clover action at β = 5.85 and 6.15*We repeat our original simulations of the hybrid meson spectrum using the clover action, as a check on lattice artifacts. Our results for the 1−+ masses do not substantially change. We present preliminary results for the wave function of the 1−+ state in Coulomb gauge.Clover action; Quark spectroscopy1999-03
247 DeTar, CarletonExotic mesons in quenched lattice QCDSince gluons in QCD are interacting fundamental constituents just as quarks are, we expect that in addition to mesons made from a quark and an antiquark, there should also be glueballs and hybrids ~bound states of quarks, antiquarks, and gluons!. In general, these states would mix strongly with th...Hybrid mesons; Antiquarks1997-12
248 Vardeny, Zeev ValentineExperimental determination of the charge/neutral branching ratio η in the photoexcitation of ∏-conjugated polymers by broadband ultrafast spectroscopyWe demonstrate a long-sought reliable method for determining the important branching ratio η between photogenerated charged polarons and neutral excitons in ∏-conjugated polymer films and solutions, using femtosecond transient photomodulation spectroscopy with broad spectral range from 0.14 to ...pi-conjugated polymers; Charge/neutral branching ratio; Photoexcitation; nu value; Broadband ultrafast spectroscopy2007-02
249 Boehme, ChristophExperimental discrimination of geminate and non-geminate recombination in a-Si:HA study of charge-carrier recombination in intrinsic hydrogenated amorphous silicon (a-Si:H) is presented using pulsed electrically and pulsed optically detected magnetic-resonance spectroscopies in order to measure the influence of spin-dependent recombination on photoluminescence (PL) and photoc...Geminate recombination2009-05
250 Lupton, John MarkExperimental evidence for exciton scaling effects in self-assembled molecular wiresResonant Rayleigh scattering from self-assembled one-dimensional molecular J-aggregate wires reveals a distinct dependence of the exciton energy on the width of lateral extension. For the J aggregates used in this study, strong in-line dipole coupling leads to a delocalization of the exciton wave fu...Exciton scaling effects; Molecular wires; J-aggregate wires; Quantum wires2004-12
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