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Description: This is the first of two papers in which the low-temperature properties of liquid He{sup 3} are to be calculated in the thermodynamically consistent 'T-matrix' approximation. The set of coupled integral equations which are to be solved is exhibited in Part A of this paper. Part B of this paper is devoted to a preliminary, zero-temperature calculation which employs the additional approximations of using separable potentials and a noninteracting spectral function to define the interaction of two particles in the medium: the <T>{sub 0} approximation. In this approximation they obtain a spectral function for the quasi particles which they expect to display general features in common with those of the actual spectral function. Using this spectral function, they calculate the thermodynamic properties of the system and find that they compare favorably to those obtained in other calculations.
Date: November 17, 1965
Creator: Beck, Donald E. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Abrupt onset of a second energy gap at the superconducting transition of underdoped Bi2212

Description: he superconducting gap--an energy scale tied to the superconducting phenomena--opens on the Fermi surface at the superconducting transition temperature (Tc) in conventional BCS superconductors. In underdoped high-Tc superconducting copper oxides, a pseudogap (whose relation to the superconducting gap remains a mystery) develops well above Tc (refs 1, 2). Whether the pseudogap is a distinct phenomenon or the incoherent continuation of the superconducting gap above Tc is one of the central questions in high-Tc research3, 4, 5, 6, 7, 8. Although some experimental evidence suggests that the two gaps are distinct9, 10, 11, 12, 13, 14, 15, 16, 17, 18, this issue is still under intense debate. A crucial piece of evidence to firmly establish this two-gap picture is still missing: a direct and unambiguous observation of a single-particle gap tied to the superconducting transition as function of temperature. Here we report the discovery of such an energy gap in underdoped Bi2Sr2CaCu2O8+delta in the momentum space region overlooked in previous measurements. Near the diagonal of Cu?O bond direction (nodal direction), we found a gap that opens at Tc and has a canonical (BCS-like) temperature dependence accompanied by the appearance of the so-called Bogoliubov quasi-particles, a classical signature of superconductivity. This is in sharp contrast to the pseudogap near the Cu?O bond direction (antinodal region) measured in earlier experiments19, 20, 21.
Date: May 26, 2007
Creator: Hussain, Zahid; Lee, W.S.; Vishik, I.M.; Tanaka, K.; Lu, D.H.; Sasagawa, T. et al.
Partner: UNT Libraries Government Documents Department

Cyclotron resonance and quasiparticles

Description: This introductory paper contains personal perspectives about the importance of cyclotron resonance in forming our modern view of solids. The papers following this one will discuss the discovery, refinements, and some of the latest developments. Although I will touch on some of these subjects, I leave the details to the other authors and in the main focus on the conceptual impact of the work. I propose that it was experiments based on cyclotron resonance which established the quasiparticle concept.
Date: January 15, 2005
Creator: Cohen, Marvin L.
Partner: UNT Libraries Government Documents Department

Composite fermion excitations in fractional quantum Hall systems

Description: In two dimensional systems in a strong magnetic field, electrons can be transformed into composite Fermions (CF) by attaching to each a fictitious flux tube (carrying flux {Phi}) and fictitious charge q, where the product q{sup {Phi}} is a multiple of 2 {Pi}. In the mean field approximation, this transformation converts a fractionally filled electron Landau level into an integrally filled CF Landau level. This integrally filled CF Landau level corresponds to the ground state of a Laughlin incompressible fluid. Excited states are described by the n{sub QE} and n{sub QH}, the numbers of quasielectron and quasihole CF excitations. For N electrons on the surface of a sphere the energy and angular momentum of a quasihole (or quasielectron) are {var_epsilon}{sub QH} and l{sub QH}=1/2(N+n{sub QH}-n{sub QE}-1) (or {var_epsilon}{sub QE} and l{sub QE}=l{sub QH}+1). The lowest energy sector of the energy spectrum contains the minimum number of CF excitations consistent with the value of N and the degeneracy of the lowest Landau level, 2S+1. The first excited sector contains one additional QE-QH pair. The total angular momentum L is obtained by adding the angular momenta of QE excitations and QH excitations treated as distinguished sets of Fermions. In the absence of CF interactions, all states containing n{sub QE} quasielectrons and n{sub QH} quasiholes are degenerate. The interaction between CF excitations partially removes this degeneracy. The interactions between CF excitations can be determined by comparing exact numerical results for N electrons with the CF picture. This amounts to constructing a Fermi liquid theory of CF excitations, and should allow the study of low lying excitations of systems with much larger values of N than can be treated numerically.
Date: April 1, 1995
Creator: Quinn, J.J.
Partner: UNT Libraries Government Documents Department

Theoretical studies of magnetic systems. Final report, August 1, 1994--November 30, 1997

Description: During the grant period the authors have studied five areas of research: (1) low dimensional ferrimagnets; (2) lattice effects in the mixed valence problem; (3) spin compensation in the one dimensional Kondo lattice; (4) the interaction of quasi particles in short coherence length superconductors; and (5) novel effects in angle resolved photoemission spectra from nearly antiferromagnetic materials. Progress in each area is summarized.
Date: December 31, 1997
Creator: Gor`kov, L.P.; Novotny, M.A. & Schrieffer, J.R.
Partner: UNT Libraries Government Documents Department

Non-Equilibrium Superconductivity and Quasiparticle Dynamics in YBaCuO

Description: The authors use optical pump, coherent terahertz probe spectroscopy to transiently excite nonequilibrium populations of quasiparticles in YBa{sub 2}Cu{sub 3}O{sub 7.{delta}} and monitor, with picosecond resolution, the superfluid and quasiparticle dynamics.
Date: May 21, 1999
Creator: Siders, J.L.W.; Jacobs, R.N.; Siders, C.W.; Trugman, S.A. & Taylor, A.J.
Partner: UNT Libraries Government Documents Department

Quasiparticle theory of electron excitations in solids

Description: A first-principles quasiparticle approach to electron excitation energies in solids is reviewed. The theory has been applied to explain and predict the spectroscopic properties of a variety of systems including bulk crystals, surfaces, interfaces, clusters, defects, and materials under pressure. Several illustrative applications are presented and some recent theoretical developments discussed.
Date: October 1, 1995
Creator: Louie, S. G.
Partner: UNT Libraries Government Documents Department

Nonlinear electrodynamics in cytoskeletal protein lattices

Description: Cytoskeletal lattice proteins including microtubules are particularly involved in dynamic regulation of intracellular movements and activities. This paper considers possibilities and implications of biological information processing due to coupling of Davydov solitons, Frohlich coherent oscillations and other nonlinear electrodynamic phenomena to conformational states of the grid-like polymer subunits of cytoskeletal microtubules. 39 references.
Date: January 1, 1983
Creator: Hameroff, S.R.; Smith, S.A. & Watt, R.C.
Partner: UNT Libraries Government Documents Department

Pion Contributions to the Electromagnetic Interaction with a Nucleus

Description: A theoretical approach to describing the electromagnetic interaction in hadronic field theories containing charged mesons at finite baryon density is presented. Path-integral methods and bilocal auxiliary fields are used to identify covariant, gauge-invariant levels of approximation, which sum infinite classes of Feynman diagrams. At the lowest level an isolated nucleon acquires a nontrivial electromagnetic structure, and the finite-density nucleus is described as a noninteracting system of quasi particles with that structure.
Date: January 1, 1992
Creator: Frank, Michael
Partner: UNT Libraries Government Documents Department

Spin Orbit Effects and Superconductivity in Oxide Materials

Description: In a variety of materials superconductivity is associated with the existence of a quantum critical point (QCP). In the case of the hole doped cuprates there is evidence which suggests that the important quantum degrees of freedom near the superconducting critical point are localized charge and spin density fluctuations. We argue that if these degrees of freedom are strongly coupled by spin-orbit interactions, a new type of quantum criticality arises with monopole-like quasi-particles as the important quantum degrees of freedom,. In layered material this type of quantum criticality can be modeled using a 2-dimensional non-linear Schrodinger equation with an SU(N) gauge field. We exhibit a pairing wave function for quasi-particles that has topological order and anisotropic properties. The superconducting transition would in some respects resemble a KT transition.
Date: September 29, 2005
Creator: Chapline, G F
Partner: UNT Libraries Government Documents Department

Dynamics of the optically-induced properties of a small-polaronic glass

Description: The relaxation and recombination of an electronic excitation created by the absorption of a super-band-gap photon is considered for a system in which excitons and charge carriers find it energetically favorable to self-trap. The notions of a barrier to self-trapping, a short-range repulsion between electrons and holes, and the electromodulation of the small-polaron absorption band play a central role in this discussion. The results are consistent with experiments on chalcogenide glasses.
Date: January 1, 1979
Creator: Emin, D.
Partner: UNT Libraries Government Documents Department

Spin and charge dynamics of chromium alloys

Description: Both the spin- and charge-density waves of Cr alloys are produced by the Coulomb attraction between electrons and holes on nearly nested Fermi surfaces. Driven by quasi-particle transitions, transverse spin- wave and longitudinal phason modes are associated with rotational and translational symmetries of pure Cr and its dilute alloys. At low frequencies, both spin and charge phasons have a nearly linear dispersion with a mode velocity which approaches the spin-wave velocity as T approaches T{sub N} or as the mismatch between the Fermi surfaces increases.
Date: July 1, 1996
Creator: Fishman, R.S.; Viswanath, V.S. & Liu, S.H.
Partner: UNT Libraries Government Documents Department

Raman study of ``boson peak`` in ion-implanted GaAs: Dependence on ion dose and dose rate

Description: Findings on the amorphization of GaAs were interpreted in the fractal model and correlated with recent analysis of ion-induced damage from Raman and ion channeling data. The Raman spectra were decomposed on phonon-fracton cruve and Gaussian bands by fitting. Crossover frequency {omega}{sub col} between phonon and fracton regimes and the fractal exponent ({sigma}+d-D){tilde d}/D shows a pronounced dependence on applied ion dose and weak dependence on dose rate. Evolution of the fractal component is compared with ion channeling and Raman spectra of phonon bands. The fractal component is strongly dependent on ion dose and is the amorphous component and is weakly dependent on dose rate. It indicates that the fractal component is not connected with point crystalline defects, to which ion channeling is particularly sensitive. The fractal correlation length {xi} and spectral dimension d, calculated from crossover frequency and fractal exponent, changes from {xi}=6A and {tilde d}=0.2 for weakly damaged samples to {xi}=10A and {tilde d}=0.8 for completely amorphized samples.
Date: November 1, 1993
Creator: Ivanda, M.; Desnica, U.V. & Haynes, T.E.
Partner: UNT Libraries Government Documents Department

3-D structures and intrinsic defects in trans-polyacetylene

Description: We report first-principles local-density functional pseudopotential calculations of static and dynamic electronic structure properties of crystalline 3-D trans--(CH)/sub x/. We find a broken symmetry ground state of P2/sub 1//a symmetry with in-phase dimerizations. Using a Green's function technique, we show that the 3-D character of the electronic band edge states strongly suppresses self-trapping, destabilizing polarons and possibly bipolarons as well in perfectly ordered 3-D trans--(CH)/sub x/. 26 refs.
Date: January 1, 1989
Creator: Vogl, P. & Campbell, D.K.
Partner: UNT Libraries Government Documents Department

Interactions between small-polaronic particles in solids

Description: When a light particle in a solid composed of relatively heavy atoms is associated with substantial displacements of the equilibrium positions of the atoms immediately surrounding it, the composite entity may be regarded as being small polaronic. Many instances of self-trapping of electronic charge carriers, excitons and light atoms such as hydrogen are known. A significant contribution to the interaction between such particles results from interference between their atomic displacement patterns. As a result oppositely charged small polarons may experience an intermediate-range repulsion, while both like-signed and neutral entities may have a tendency to cluster. These effects can be very important. As examples, the recombination kinetics of electron and hole small polarons and the ordering of defect atoms are discussed.
Date: January 1, 1980
Creator: Emin, D.
Partner: UNT Libraries Government Documents Department

Measurements of photo-induced changes in conjugated polymers

Description: We have used the highly sensitive technique of Photothermal Deflection Spectroscopy (PDS) to measure changes in the infrared absorption spectra of MEHPPV, P3HT and Polydiacetylene-4BCMU induced by pumping these polymers with light above the {pi}--{pi}* transition energy. In contrast to previous chopped light transmission measurements of these effects, the PDS technique can directly measure the buildup or decay of the absorption coefficient, {alpha}, on the time scale of second to days. In the case of MEHPPV we observe that the time scale of seconds to days. In the case of MEHPPV we observe that above-gap light causes the appearance of a broad infrared peak in {alpha}, which continues to grow-in hours after the pump light is first applied. For this polymer the general shape of the absorption spectra in the unpumped state mimics the photo-induced changes, suggesting that remnant photo-induced states determine the maximum transparency observed under normal experimental conditions. For P3HT and to a lesser extent, MEHPPV, we also observe irreversible photo-induced absorption components which we tentatively identify with photo-induced oxidation of the polymer matrix. 10 refs., 8 figs.
Date: January 1, 1991
Creator: Seager, C.H.; Sinclair, M.B. (Sandia National Labs., Albuquerque, NM (USA)); Mc Branch, D.; Heeger, A.J. (California Univ., Santa Barbara, CA (USA)) & Baker, G.L. (Bell Communications Research, Inc., Red Bank, NJ (USA))
Partner: UNT Libraries Government Documents Department

Nonlinear discrete models for DNA dynamics

Description: In this paper we report the investigations on a problem related to DNA dynamics: thermal generation of localized pulses that are called solitons. The thermal generation of solitons in circular homogeneous DNA is investigated by calculating the number of solitons as a function of the absolute temperature. These calculations are effected by using two different models for the DNA molecule. In both models the parameters are chosen to match experimentally measured properties of the molecule. We find that a significant number of solitons is generated at physiological temperatures, and a T{sup 1/3} law is followed at low temperatures. 20 refs., 2 figs.
Date: August 1, 1989
Creator: Muto, V.; Scott, A.C.; Christiansen, P.L.; Lomdahl, P.S. (Los Alamos National Lab., NM (USA); Technical Univ. of Denmark, Lyngby (Denmark). Lab. of Applied Mathematical Physics & Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Electron-electron interaction effects in quasi-one-dimensional conducting polymers and related systems

Description: We review recent results on the role of electron-electron (e-e) interactions in quasi-one-dimensional conducting polymers and related systems. Within the Peierls-Hubbard model, the effects of both short-range (on-site U and nearest neighbor V/sub 1/) and long-range (V/sub j/, jgreater than or equal to 2) are examined, the former using quantum Monte Carlo and the latter with exact diagonalization of finite size systems and analytic arguments. We also discuss optical absorption properties in the presence of electronic correlation, focusing on the weak and strong coupling limits.
Date: January 1, 1986
Creator: Campbell, D.K.; Baeriswyl, D. & Mazumdar, S.
Partner: UNT Libraries Government Documents Department