UScholar Works
 
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101 - 125 of 924
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CreatorTitleDescriptionSubjectDate
101 Symko, Orest GeorgeEffect of RKKY interactions on the magnetization of dilute magnetic alloys with hcp hostsThe magnetization due to the presence of magnetic impurities dissolved dilutely in nonmagnetic H.C.P. host metals has been calculated assuming a fine structure splitting by an axially symmetric crystal field and an RKKY interaction between the impurities. To compute the RKKY contribution, the inte...RKKY interactions; Dilute magnetic alloys; HCP hosts; MgMn; ZnMn1981
102 Vardeny, Zeev ValentineRelaxation of photoinduced sub-bandgap absorption in a-Si:HThe decay of photoinduced sub-bandgap absorption (PA) following pulsed excitation was studied in the temperature range 80 - 305K, in a-Si:H samples prepared by glow discharge and sputtering. The decay was interpreted in terms of bimolecular diffusion limited recombination involving dispersive trans...Photoinduced absorption; Sub-bandgap absorption; Glow discharge; Sputtering; Decay1981
103 Ailion, David CharlesEvidence for elastic disorder in the elastically ordered phase of KCNWe have obtained evidence from 1 3C NMR measurements that the CN~ ion in the elastically ordered phase of KCN is misoriented slightly with respect to the orthorhombic b axis. This misorientation varies randomly over the lattice, averaging to zero on a macroscopic scale. The misorientations are mani...Potassium cyanide; Anisotropy; Orthorhombic crystal; NMR; Nuclear magnetic resonance1981
104 Mattis, Daniel C.Eigenfunction localization in dilute lattices of various dimensionalitiesAs a fraction of bonds p is removed from a lattice, we find a threshold PQ above which all eigenstates are nonpropagating (Anderson localized). This occurs well before the classical percolation threshold. For example, in two dimensions where the classical threshold is pc = 1/2 , we find PQ = 0.Eigenstates; Dilute lattices1981-05
105 Vardeny, Zeev ValentineHot-carrier thermalization in amorphous siliconThermalization of photoinduced carriers in a-Si and α-Si:H was studied with use of sub-picosecond-pump and probe techniques with parallel and perpendicular polarizations. The underlying process was identified as hot-carrier absorption whose cross section increases with the carrier excess energy. T...Amorphous silicon; Thermalization; Photoinduced carriers; Frohlich interaction1981-05
106 Vardeny, Zeev ValentinePhonon polariton study of CuCl1-x BrxThe optical-phonon spectrum of CuCI-x Brx at low temperature is very unusual in regard to many of its properties. Despite the apparent two-mode behavior our measurements illustrate anomalies in the Raman intensity and temperature-induced frequency shift, as well as in the oscillator strengths yiel...Cuprous halides; CuCl1-x Brx1981-08
107 DeTar, CarletonQuark-bag model with low-energy pion interactions. II. ApplicationThe hybrid pion-quark-bag model discussed in I is applied to a calculation of masses, pion couplings, and other parameters of various light hadrons in an effort to determine the extent to which the bag parameters must be modified in the presence of pion interactions. Corrections for the finite spr...Bag models; Quark bag; Chiral symmetry; Pion field; Nucleons1981-08
108 DeTar, CarletonQuark-bag model with low-energy pion interactions. I. TheoryA standard method for restoring chiral symmetry in the bag model is to introduce an explicit external pion field. Questions of the consistency and compatibility of this method with the assumptions of the static-cavity approximation of the bag model are discussed. An approximate version of the mode...Bag models; Quark bag; Chiral symmetry; Pion bag; Pion field1981-08
109 Sokolsky, PierreMeasurement of elastic νμ and ν̄μ scattering on protonsWe have measured elastic vµ and vµ scattering on protons at the Brookhaven National Laboratory Alternating Gradient Synchrotron. We find RNC = σ (νµp → vµp)/σ (vµp -* vµp) = 0.44 ±0.12 and Rvµ = σ (vµp → vµp)/σ (vµn → µ-p) =0.11 ±0.03. The elastic Q2 distribution is in good a...1981-09
110 Mattis, Daniel C.; Sutherland, BillAmbiguities with the relativistic δ-function potentialIn many cases of physical interest, the 6-function potential is a very convenient approximation to more structured, and more difficult, short-ranged potentials. In relativistic theories, its use is often mandated because only a mathematical point has a relativistically invariant shape. Neverthele...Delta function; Energy states1981-09
111 Vardeny, Zeev ValentineOptical picosecond studies of hot carriers in amorphous semiconductorsThermalization of photogenerated carriers in a-Si, a-Si:H, a-As2Se3 and a-Se was studied by measuring the photoinduced absorption with subpicosecond resolution. The thermalization process can be described by Frohlich interaction with polar phonons in a-Si:H and a-As2Se3 but not in a-Si. Using photo...Photogenerated carriers; Thermalization1981-10
112 Vardeny, Zeev ValentineTime resolved spectroscopy of photoinduced absorption in glow-discharge a-Si:HThe time and temperature dependence of the photoinduced absorption spectra was measured in glow-discharge a-Si:H in the energy range 0.7 to 1.4 eV, temperature interval 10 to 306K and time domain 2 ys to 2 ms. The results are consistent with a model based on thermalization of excess carriers in tra...Photoinduced absorption; Glow-discharge a-Si:H; Thermalization; Excess carriers; Trap states; Time dependence; Temperature dependence1981-10
113 Vardeny, Zeev ValentinePicosecond dynamics of carriers in amorphous semiconductorsUsing time resolved photoinduced absorption with subpicosecond resolution we studied hot carrier thermalization followed by deep trapping and recombination in a-Si, a-Si:H, a-Si:F, a-Si:H:F and a-As2Se3. In a-Se and a-As2S3_xSex (0.25 < x < 0.75) the observed relaxations were attributed to geminat...Excess carriers; Thermalization1981-10
114 Mattis, Daniel C.Theory of the magnetic polaronWe construct exact Green's functions for a single electron in a ferromagnetic semiconductor, including both spin-conserving and spin-flip processes at T = 0. We contrast two cases: ferromagnetic and antiferromagnetic coupling of the electron's spin to the lattice. In the former case, a small-k elect...Scattering states; Electric transport1981-11
115 Mattis, Daniel C.Phase transition of model interacting chainsThe partition function of n interacting chains having a phase transition at Tc(n) is reduced, by the transfer-matrix formalism, to the determination of an w-body bound state in one dimension. Subject to mild restrictions on the potentials, this w-body problem can be analyzed in terms of a two-body p...Phase transition; Interacting chains1981-12
116 Symko, Orest GeorgeTemperature dependence of the order parameter in a dilute AgMn spin glassThe magnetization of a dilute AgMn spin glass containing 150 ppm Mn has been measured over the temperature range from 20 mK to 2 K in an applied field of 0.9 Oe, using a SQUID magnetometer. A comparison of the measured magnetization with numerical calculations of the magnetization based on the Mean ...AgMn spin glass; Mean random field; MRF; Temperature dependence; Order parameter; RKKY interactions1982
117 Symko, Orest GeorgeSuperconducting microphone for photoacoustic spectroscopyA superconducting microphone has been developed for photoacoustic spectroscopy at low temperatures. The microphone consists of a thin mylar membrane coated with a film of lead whose motion is detected by SQUID magnetometer. For the simple set-up presented here, the limiting pressure sensitivity is ...Superconducting microphone; Photoacoustic spectroscopy; Low temperatures1982
118 Mattis, Daniel C.Decay of electron waves in a random mediumThis paper reports calculation of the time-correlation function of an electron wave of given wave vector k in a three-dimensional medium with weak scatterers randomly distributed. An initial parabolic decay is followed by the usual exponential law which, asymptotically, gives way to a 1/t3 law.Scattering; Potential; Coupling1982
119 Vardeny, Zeev ValentinePicosecond photoinduced transmission associated with deep traps in phosphorous doped α-Si:HPhotoinduced transmission was observed in the picosecond time domain in phosphorusdoped a-Si:H and connected with deep hole traps produced by doping. The hole transport was found to be dispersive starting before 5 ps and temperature dependent. This shows that the energy distribution of shallow traps...Photoinduced transmission; Deep traps; Amorphous silicon; Phosphorous doped a-Si:H; Electronic relaxation response1982-04
120 Symko, Orest GeorgeEffect of crystal field on the magnetization of dilute hcp alloysMagnetization measurements on very dilute single-crystal alloys of Mg-Mn, Zn-Mn, and Zn-Cr in the temperature range of 2-0.008 K show that the ground state of these systems is determined by fine-structure splitting. For Mg-Mn the fine-structure constant D is +0.006 K with an effective spin of f whil...HCP alloys; Crystal field; Magnetization; Mg-Mn; Zn-Mn; Zn-Cr1982-04
121 Symko, Orest GeorgeSpin-glass behavior in dilute magnetic alloys with hcp structureA simple physical model is presented for calculating the magnetization of dilute magnetic systems with hep hosts which incorporates elements of both crystal-field theory and the molecular-field theory of spin-glasses. To permit the computation of the Ruderman-Kittel-Kasuya-Yosida contribution, the i...Spin-glass behavior; HCP structure; HCP alloys; Dilute magnetic systems; Molecular-field theory; MgMn; ZnMn1982-05
122 Mattis, Daniel C.Bound exciton and hole: an exactly solvable three-body model in any number of dimensionsA three-body problem, concerning two holes in a nondegenerate valence band and a single electron in a conduction band, with strong short-range interactions, is solved exactly in any number of dimensions. The binding depends nontrivially on the ratio of the valence to conduction bandwidths (i.e., on ...Three-body problem; Trion; Bond energies1982-09
123 Vardeny, Zeev ValentinePicosecond photoinduced dichroism in trans-(CH)x: direct measurement of soliton diffusionPhotoinduced dichroism caused by bleaching of the interband transition in tran s-(CH)x was observed in the picosecond time domain,, The bleaching is induced instantaneously and decays with time as £~1 / / 2 , changing to a lower power after ~50 psec. Although the photoinduced bleaching persists to...Photoinduced dichroism; Trans-(CH)x1982-11
124 Vardeny, Zeev ValentinePicosecond trapping of photocarriers in amorphous siliconTrapping of photoexcited carriers in the picosecond and subnanosecond time domains was studied by measuring the decay of photoinduced absorption (PA) in a-Si, a-Si:F, a-Si:H, and a-Si:H:F. We found that when the midgap density of states decreases, both the trapping time and its temperature dependenc...Photocarriers; Amorphous silicon; Picosecond trapping; Photoinduced absorption1983
125 Mattis, Daniel C.Application of tridiagonalization to the many-body problemThe problem of a single magnetic, Wolff-model impurity in an otherwise ideal metallic host is investigated using the nonperturbative Lanczos method. Convergence is very rapid. The many-body ground-state energy is investigated and comparisons are made with Tomonaga operator theory and other weak-coup...Lattice; Electrons; Interaction; Ground-state energy; Tridiagonalization; Magnetic impurity; Nonmagnetic metals1983
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