UScholar Works
 
Filters: Department: "Physics" Collection: "ir_uspace"
126 - 150 of 924
Number of results to display per page
CreatorTitleDescriptionSubjectDate
126 Vardeny, Zeev ValentinePhotoinduced IR active vibrations in trans-(CD)x: a three-mode systemIn a recent Letter Blanchet et al.? have extended photoinduced absorption measurements of frYms-polyacetylene to lower energy than obtained before 2 for both isotopes, (CH)x and (CD)X. While in (CE)X three strong ir-active vibrations (IRAV) are photoinduced, only two IRAV were observed in (CD)X, at...Photoinduced absorption; IR active vibrations1983
127 Ailion, David CharlesFloating of the modulation wave and phase pinning in incommensurate Rb2ZnBr4Nuclear-magnetic-resonance measurements in incommensurate Rb2ZnBr4 show the existence of regions where the modulation wave is floating. The floating regions coexist with other regions where the modulation wave is static. Impurity phase pinning and a roughening of the modulation wave at higher temper...Floating; Incommensurate phase; Phason mode; Lattices1983
128 Mattis, Daniel C.Effect of spin variables and exciton motion on ground-state properties of the "trionWe solve a quantum three-body problem involving two holes and a single electron ("trion") in a two-band Hubbard model. The particles' spin and the exciton hopping matrix element are all included. We compare the results with those of a previous paper, in which these additional complications were abs...Three-body problem; Trion; Bond energies1983-03
129 Mattis, Daniel C.Odd-spin-cluster interactionsWe consider interactions of Ising spins three at a time, five at a time, etc., as distinguished from the conventional interactions (two at a time). To illustrate, we calculate the exact thermodynamics of three-spin-cluster interactions in one dimension with and without a magnetic field. We find regu...Ising spins; Binary clusters1983-03
130 Mattis, Daniel C.Nonlinear lattice dynamics in two dimensionsIn general, dynamical and quantum-mechanical properties of anharmonic lattices are best expressed in terms of bond variables. A transformation from atomic (site) to bond coordinates is generated in two dimensions, with the help of a number of subsidiary conditions expressed on plaquettes. It is sho...Phonons; Plaquettes; Harmonic oscillators; Ferromagnets1983-04
131 Mattis, Daniel C.Eigenstates of N excitons and one holeWe solve for the eigenstates and energy eigenvalues of N immobile Frenkel excitons (a relatively trivial proposition) and of N such excitons plus one hole (which for large N can only be done in one dimension). We also guess that a charged globule, consisting of N excitons and O(N) holes, can be stab...Eigenstates; Frenkel excitons; Many-body problem1983-04
132 Vardeny, Zeev ValentinePhotogenerated gap states in polyacetyleneWe have measured the optical absorption spectrum of photogenerated gap states in polyacetylene, (CH)X . From a comparison with electroabsorption spectra the charge state of the excitations is determined. In both isomers of (CH)X locally neutral (exciton-like) states are observed. In addition a charg...Gap state; Photoexcitation1983-06
133 Vardeny, Zeev ValentinePhoto induced infrared active phonons in trans polyacetyleneWe measured photogenerated ir active phonons in trans-(CH) by the photoinduced absorption technique. A correlation was found to exist with a photoinduced absorption band in which electronic transitions are involved. Our results show photoproduction of free charged defects with long lifetimes.Photoinduced phonons; Trans polyacetylene1983-06
134 Vardeny, Zeev ValentinePhotoinduced infrared activity in polyacetylenePhotoexcitation of trans - but not cis -polyacetylene, results in the appearance of strongly-ir-active local modes at 1370 and 1260 cm-1. This observation demonstrates that the photogeneration of self-localized charge carriers is unique to the trans isomer. In spite of their localization the kineti...Photoinduced infrared activity; Photoexcitation1983-06
135 Vardeny, Zeev ValentinePicosecond photoinduced optical anisotropy in trans-(CH)x : direct measurement of soliton diffusionPhotoinduced dichroism caused by bleaching of the interband transition in trans - (CH)X was observed in the picosecond time domain. The bleaching is induced instantaneously and decays with time as t - 1 / 2 , changing to a lower power after ~ 50 ps. Although the photoinduced bleaching persists to l...Trans-(CH)x; Soliton diffusion; Bleaching; Photoinduced dichroism1983-06
136 Vardeny, Zeev Valentine; Ehrenfreund, Eitan A.Resonant Raman scattering from amplitude modes in trans-(CH)x and -(CD)xThe three resonantly enhanced Raman vibrations in trans-(CK)x and ~(CD)X are described in terms of amplitude modes associated with the Peierls gap. The dispersion in the Raman-line profiles is explained by inhomogeneity. A narrow distribution of the effective electron-phonon coupling constant is re...Peierls gap1983-12
137 Williams, Clayton C.High resolution photothermal laser probeAt frequencies near 1 GHz, the acoustic wavelength in argon gas becomes half that of visible light, making possible collinear Bragg scattering of laser light by the sound. This acousto-optic interaction has been used to detect photothermally generated acoustic power at the surface of solids. This ne...Photothermal laser probe; Silicon wafer1984
138 Vardeny, Zeev ValentinePhotoinduced absorption spectra in amorphous Si:H and Ge:H and microcrystalline Si:HThe steady state subgap photoinduced absorpotion bands in a-Ge:H and a-Si:H are interpreted in terms of two kinds of optical transitions of photoexcited carriers from traps in the gap into the bands of which one produces absorption and the other produces bleaching. The photoinduced absorption in mic...Photoinduced absorption; Si:H; Ge:H; Amorphous silicon; Amorphous germanium; Microcrystalline silicon1984
139 Vardeny, Zeev ValentinePhotoconductivity and photoinduced absorption in a-Si:F and a-Si:HThe photoconductivity (PC) and photoinduced absorption (PA) of RF glow discharge a-Si:F and a-Si:H samples is reported. The value of the room temperature PC of a-Si:F is lower by some four orders of magnitude relative to that of a-Si:H, but the PA of a-Si:F is found to be significantly higher than t...Photoinduced absorption; a-Si:F; a-Si:H; RF glow discharge; Spin densities1984
140 Vardeny, Zeev ValentinePicosecond optical generation and detection of phonon waves in a-As2Te3Using the pump and probe technique we have observed oscillations of photoinduced transmission in thin films of a-As2Te3. The oscillations have periods of 70-240 ps, depending on sample thickness. We ascribe these to phonon propagation in the films. Thermal expansion and carrier deformation potenti...Picosecond optical generation; a-As2Te3; Pump and probe technique1984
141 Mattis, Daniel C.What is the effective mass of an exciton?In the effective-mass approximation, the mass M* of an exciton is just the sum of the electron and hole masses, me*+ mh*. However, the effective-mass approximation is invalid if the forces are strong. Here we derive a plausible formula for the n th bound state of the exciton: Mn*= (me* + mh*) / (...Kinetic; Energy; Electron1984
142 Wu, Yong-ShiMassless fermions and Kaluza-Klein theory with torsionA pure Kaluza-Klein theory contains no massless fermion in four-dimensional theory. We investigate the effect of introducing torsion on the internal manifold and find that there are massless fermions. The hope is that given an isometry group the representation to which these fermions belong is fixe...Massless fermions; Four-dimensional theory; Torsion1984
143 Mattis, Daniel C.Three-body bound states on a latticeThe theory of three-body bound states for particles moving on a lattice and interacting with attractive two-body pointlike potentials is presented. The applications are to bosons, fermions (no three-body bound states are found), and magnons. When a three-body bound state forms in three dimensions, i...Particle; Fermions; Ferromagnet1984
144 Ailion, David CharlesMolecular reorientations in the ordered phases of KCN and NaCN studied by NMRWe have measured 13C and 23Na NMR spin-lattice relaxation times as a function of temperature in KCN and NaCN in order to study the head-to-tail reorientations of the CN- molecules in the two low-temperature ordered phases. We have combined our data with those of dielectric-response and ionic-thermal...Spin; Interactions; Fluctuations1984
145 Mattis, Daniel C.Phonon model of vacancy-interstitial pair formation in solidsBonds between neighboring atoms in a solid are imperfect harmonic oscillators. Through consideration of the nonlinearities, it is shown that vacancy-interstitial defect pairs can be described in terms of phonon dynamical variables. The effective spring constants are determined by self-consistency...Harmonic; Potential; Homogeneous1984
146 Vardeny, Zeev ValentineOptical bias control of dispersive relaxations in α-Si:HRelaxation of the photoinduced ir absorption band in α-Si:H was studied in the microsecond time domain as a function of cw bias illumination. The decays follow a power law t-α where the dispersion parameter a increases with bias illumination. At low temperatures, a increases linearly with the st...Optical bias control; Dispersive relaxations; a-Si:H; Amorphous silicon1984-01
147 Vardeny, Zeev ValentineOptical bias control of dispersive relaxations in α-SI:HRelaxation of the photoinduced ir absorption band in a-Si:H was studied in the microsecond time domain as a function of cw bias illumination. The decays follow a power law t-a where the dispersion parameter a increases with bias illumination. At low temperatures, a increases linearly with the stead...Optical bias; Dispersive relaxations; Amorphous silicon; a-Si:H; Photoinduced absorption; Bias-controlled tunneling; Multiple trapping1984-01
148 Sokolsky, PierreTotal proton-proton cross section at s1/2=30 TeVWe have measured the proton-air inelastic cross section at s 1/2 = 30 TeV by observing the distribution of extensive-air-shower maxima as a function of atmospheric depth. This distribution has an exponential tail whose slope is λ = 72 ±9 g c m - 2 which implies that σ inel p-air = 530 ± 66 mb. U...1984-04
149 Wu, Yong-ShiGeneral theory for quantum statistics in two dimensionsBecause of complicated topology of the configuration space for indistinguishable particles in two dimensions, Feynman's path-integral formulation allows exotic statistics. All possible quantum statistics in two-space are characterized by an angle parameter 9 which interpolates between bosons and fe...Homotopy classes1984-06
150 Mattis, Daniel C.Application of tridiagonalization to the many-body problem. II. Finite TIn a previous paper of the same title, we obtained the ground-state energy of a magnetic (Wolff-model) impurity in a nonmagnetic metal. In the present Brief Report, we calculate the impurity's contribution to the density of states and heat capacity of the metal at low temperatures. Here, the Lancz...Ground-state energy; Tridiagonalization; Magnetic impurity; Nonmagnetic metals; Heat capacity1984-06
126 - 150 of 924