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Amplitude Modulation of Atomic Wavefunctions - Final Technical Report

Description: This project developed a novel wave function modulation technique. Other modulation techniques use tailored laser pulses to directly excite a time-dependent, modulated wave function from a ground state. Our technique began with one electron already excited to a time independent eigenfunction. Then, by using excitations of a second valence electron, we modulated the other wave function. Our technique had the benefit that it was very efficient, and required low power lasers with no need for precise phase or amplitude control. On the other hand it had the difficulty of being a multi-step laser excitation with a maximum repetition rate of 10 Hz. Over the course of this project, we showed that the technique did work, and work efficiently. However, it was easy to generalize. Since the modulation depended on a difference between electron-electron interactions with the inner electron in a ground or excited state, the efficiency of the modulation was strongly state dependent. For example, we never showed any significant modulation in our tests of barium states, while our strontium measurements did show efficient modulation as long as the state to be modulated was in the 5snd group with n between 30 and 50. We completed some studies of the dependence of the amplitude modulation as we varied the time between the excitation and de-excitation pulses applied to the inner electron. The amplitude of the nearest neighbor states was well described by Multi-Channel Quantum Defect theory, but farther satellites were problematical. This may have simply reflected the low density of measurement points, since the amplitudes of the farther satellites oscillate more quickly with time. As we developed our technique, we showed that we could directly measure autoionization decay rates in the time domain, and that the net effect of a state belonging to a Rydberg series was that exponential decay ...
Date: August 1, 2001
Creator: Cooke, William E.
Partner: UNT Libraries Government Documents Department

Angle-Resolved Photoemission Spectroscopy on Electronic Structure and Electron-Phonon Coupling in Cuprate Superconductors

Description: In addition to the record high superconducting transition temperature (T{sub c}), high temperature cuprate superconductors are characterized by their unusual superconducting properties below T{sub c}, and anomalous normal state properties above T{sub c}. In the superconducting state, although it has long been realized that superconductivity still involves Cooper pairs, as in the traditional BCS theory, the experimentally determined d-wave pairing is different from the usual s-wave pairing found in conventional superconductors. The identification of the pairing mechanism in cuprate superconductors remains an outstanding issue. The normal state properties, particularly in the underdoped region, have been found to be at odd with conventional metals which is usually described by Fermi liquid theory; instead, the normal state at optimal doping fits better with the marginal Fermi liquid phenomenology. Most notable is the observation of the pseudogap state in the underdoped region above T{sub c}. As in other strongly correlated electrons systems, these unusual properties stem from the interplay between electronic, magnetic, lattice and orbital degrees of freedom. Understanding the microscopic process involved in these materials and the interaction of electrons with other entities is essential to understand the mechanism of high temperature superconductivity. Since the discovery of high-T{sub c} superconductivity in cuprates, angle-resolved photoemission spectroscopy (ARPES) has provided key experimental insights in revealing the electronic structure of high temperature superconductors. These include, among others, the earliest identification of dispersion and a large Fermi surface, an anisotropic superconducting gap suggestive of a d-wave order parameter, and an observation of the pseudogap in underdoped samples. In the mean time, this technique itself has experienced a dramatic improvement in its energy and momentum resolutions, leading to a series of new discoveries not thought possible only a decade ago. This revolution of the ARPES technique and its scientific impact result from dramatic advances in four essential ...
Date: April 30, 2010
Creator: Zhou, X.J.
Partner: UNT Libraries Government Documents Department

Beam-beam disruption and the case for a plasma lens in e{sup {minus}}e{sup {minus}} collisions

Description: In an e{sup {minus}}e{sup {minus}} collider, the mutual disruption of the beams will significantly decrease the luminosity, different from the case of e{sup +}e{sup {minus}} colliders, where the mutual attraction of the oppositely-charged beams leads to a self-focusing effect. In this paper the authors estimate the beam disruption at SLC and NLC energies using ABEL simulations. They then give estimates of how a plasma lens might improve the luminosity in e{sup {minus}}e{sup {minus}} collisions.
Date: March 1, 1996
Creator: Chen, P.; Spitkovsky, A. & Weidemann, A.W.
Partner: UNT Libraries Government Documents Department

Beam-beam effects and generalized luminosity

Description: The assumption is made that before an NLC is approved, a prototype will be necessary that demonstrates the feasibility of a general purpose linear collider capable of {rvec e}{sup {+-}}{rvec e}{sup {+-}}, {rvec {gamma}}{rvec e} and {rvec {gamma}}{rvec {gamma}} incident channels. At an upgraded SLC, such channels could provide new physics over a range of energies upwards of a few GeV. Effects that limit the luminosity of a GLC are discussed together with their possible mitigations. The expected luminosities in the different channels are then predicted in a consistent way for {radical}s{sub ee} = 0.5 TeV.
Date: January 1, 1996
Creator: Spencer, J.E.
Partner: UNT Libraries Government Documents Department

Comments on the possible use of the SLC as an e{sup -}e{sup -} collider

Description: It has been suggested that the SLAC Linear Collider, which was designed to collide electrons with positrons, could be modified to collide electrons with electrons. A cursory examination of this suggestion leads us to conclude that such a modification is technically feasible, but by no means trivial. In this letter we outline the issues that must be addressed to realize this possibility.
Date: February 1, 1996
Creator: Erickson, R.
Partner: UNT Libraries Government Documents Department

Coulomb correlation effects in quasi-one-dimensional conductors

Description: Recent results on the role of electron-electron (e-e) interactions - ''correlation effects'' - in quasi-one-dimensional conductors are reviewed. Within the Peierls-Hubbard model, the consequences of short range (on-site U and nearest neighbor V) e-e interactions for ground state properties, nonlinear excitations, and optical absorption are examined. Techniques include quantum Monte Carlo and weak and strong coupling perturbative arguments. 26 refs., 2 figs.
Date: January 1, 1986
Creator: Campbell, D.K.; Baeriswyl, D. & Mazumdar, S.
Partner: UNT Libraries Government Documents Department

Coulomb correlations and optical gap in polyacetylene

Description: A model including both electron-phonon coupling (as in the SSH Hamiltonian) and electron-electron interactions (on-site term U, nearest-neighbor term V) is treated within the variational scheme of Gutswiller. It is shown that for weak electron-phonon coupling the primary effect is a bond-order wave induced by electronic correlation, whereas the lattice dimerization is a secondary effect. Correspondingly the optical gap is mainly due to electronic correlation.
Date: January 1, 1986
Creator: Baeriswyl, D. & Maki, K.
Partner: UNT Libraries Government Documents Department

Dimuon production by high energy neutrinos and antineutrinos in the Fermilab fifteen-foot bubble chamber. [60 and 89 GeV]

Description: The Fermilab fifteen-foot bubble chamber/two-plane External Muon Identifier (EMI) hybrid detector filled with Ne(47% atomic)-H/sub 2/ is exposed to the quadrupole triplet beam (< E/sub ..nu..//sub ..mu../ > = 89 GeV, < E/sub anti ..nu..//sub ..mu../ > = 60 GeV). In 326,000 pictures there are 10,148 neutrino and 1773 antineutrino charged current events with two-plane EMI muon identification and muon momenta > 4 GeV/c. In this sample there are 55 ..mu../sup -/..mu../sup +/X, 11 ..mu../sup -/..mu../sup -/X and 0 ..mu../sup +/..mu../sup +/X candidates with muon momenta > 4 GeV/c. The like-sign events are consistent with background. The opposite-sign dimuons occur at R/sub ..mu.. ..mu../ = 0.35 +- 0.10% of the single muon rate. The ..nu../sub ..mu../-induced ..mu../sup -/..mu../sup +/ rate is 0.20 +- 0.15% below E/sub nu//sub ..mu../ = 100 GeV and 0.50 +- 0.30% above 100 GeV. In the opposite-sign dimuons there are 10 candidates with an associated V/sup 0/ implying 0.76 +- 0.36 neutral strange particle per opposite-sign dimuon event. The production rate, excess of neutral strange particles, and kinematic distributions of the dimuon events are consistent with the charm model predictions. 56 references.
Date: September 1, 1979
Creator: Orthel, J.L.
Partner: UNT Libraries Government Documents Department

Dye- and Semiconductor-Sensitized Nanoparticle Solar Cell Research at NREL

Description: The major objective of this research program is to determine the operational characteristics key to efficient, low-cost, stable liquid-junction and solid-state solar cells based on sensitized nanoporous films (in collaboration with DOE's Office of Science Program). Toward this end, we are conducting experimental and theoretical studies to understand the unique physical and chemical factors governing cell performance. Current scientific issues addressed include the influence of film morphology, sensitizer, and electrolyte on the electron transport and recombination dynamics and on the light-harvesting, charge-injection, and charge-collection efficiencies. Recently, we investigated the relationship between (1) transport and recombination, (2) morphological factors of core-shell nanoparticle films and their PV properties, and (3) electron-electron interactions and their effect on the transport dynamics. In this paper, we discuss the connection between transport and recombination and its effect on cell performance.
Date: January 1, 2005
Creator: Frank, A. J.; Kopidakis, N.; Benkstein, K. D.; van de Lagemaat, J. & Neale, N. R.
Partner: UNT Libraries Government Documents Department

Effect of Electron-Electron Interaction on Transport in Dye-Sensitized Nanocrystalline TiO2

Description: Experimental measurements and continuous-time random walk simulations on sensitized electrolyte-infused porous nanocrystalline TiO2 films show that the actual electronic charge in the films is significantly larger than that estimated from small-perturbation methods by a constant, light-intensity-independent factor. This observation can be explained by small-perturbation techniques measuring the chemical diffusion coefficient of electrons instead of the normally assumed tracer diffusion coefficient of electrons. The difference between the two diffusion coefficients is attributed to the presence of an exponential density of states through which electrons interact. At high light intensities, an additional extra component owing to Coulomb interactions between the electrons is expected to arise.
Date: January 1, 2005
Creator: van de Lagemaat, J.; Kopidakis, N.; Neale, N. R. & Frank, A. J.
Partner: UNT Libraries Government Documents Department

Emergence of the Persistent Spin Helix in Semiconductor Quantum Wells

Description: According to Noether's theorem, for every symmetry in nature there is a corresponding conservation law. For example, invariance with respect to spatial translation corresponds to conservation of momentum. In another well-known example, invariance with respect to rotation of the electron's spin, or SU(2) symmetry, leads to conservation of spin polarization. For electrons in a solid, this symmetry is ordinarily broken by spin-orbit (SO) coupling, allowing spin angular momentum to flow to orbital angular momentum. However, it has recently been predicted that SU(2) can be recovered in a two-dimensional electron gas (2DEG), despite the presence of SO coupling. The corresponding conserved quantities include the amplitude and phase of a helical spin density wave termed the 'persistent spin helix' (PSH). SU(2) is restored, in principle, when the strength of two dominant SO interactions, the Rashba ({alpha}) and linear Dresselhaus ({beta}{sub 1}), are equal. This symmetry is predicted to be robust against all forms of spin-independent scattering, including electron-electron interactions, but is broken by the cubic Dresselhaus term ({beta}{sub 3}) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as {alpha} {yields} {beta}{sub 1}. Here we observe experimentally the emergence of the PSH in GaAs quantum wells (QW's) by independently tuning {alpha} and {beta}{sub 1}. Using transient spin-grating spectroscopy (TSG), we find a spin-lifetime enhancement of two orders of magnitude near the symmetry point. Excellent quantitative agreement with theory across a wide range of sample parameters allows us to obtain an absolute measure of all relevant SO terms, identifying {beta}{sub 3} as the main SU(2) violating term in our samples. The tunable suppression of spin-relaxation demonstrated in this work is well-suited for application to spintronics.
Date: August 24, 2011
Creator: Koralek, Jake; Weber, Chris; Orenstein, Joe; Bernevig, Andrei; Zhang, Shoucheng; Mack, Shawn et al.
Partner: UNT Libraries Government Documents Department

Extended gauge models and e{sup -}e{sup -} {r_arrow} W{sup -}W{sup -} at the NLC

Description: We briefly discuss two possible manifestations of the lepton number violating reaction e{sup -}e{sup -} {r_arrow} W{sub i}{sup -}W{sub j}{sup -}, which probes the masses and mixings of heavy Majorana neutrinos, at the Next Linear Collider (NLC). Cross sections for this process are shown to be potentially quite large at center of mass energies of order 1-1.5 TeV.
Date: October 1, 1995
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

First results from Mark II at SPEAR

Description: First results from the SLAC-LBL Mark II magnetic detector at SPEAR are presented. The performance of the detector is discussed and preliminary results are given on inclusive baryon production R/sub p + anti p/, R/sub ..lambda.. + anti ..lambda../, on decay modes of the D mesons and on two-photon production of eta' mesons.
Date: May 1, 1979
Creator: Abrams, G.S.; Alam, M.S. & Blocker, C.A.
Partner: UNT Libraries Government Documents Department

General many-body systems

Description: The problem of how to visualize and sometimes solve a general many-body system is considered. The ideas are established in the context of very simple small systems, a Hubbard model and a coupled electron-phonon model, both on two lattice sites. These models are also solved to good approximation in the thermodynamic limit, although the Hubbard model is restricted to a small number of holes away from the Mott insulating state. Response functions are also considered. A fairly general many-body Hamiltonian is considered. It consists of an electron or other fermion kinetic energy and electron-electron interactions, which may be coupled to a bose field such as a phonon. The phonons themselves may be nonlinear (have self-interactions). The system may be strongly coupled. One may also add coupling to an external driving field, such as an ac electric field. The methods discussed are nonperturbative, and so differ from the standard methods of diagrammatic perturbation theory. A comparison is made with diagrammatic methods in the context of the random phase approximation. 6 refs., 12 figs.
Date: January 1, 1989
Creator: Trugman, S. A.
Partner: UNT Libraries Government Documents Department

High-Pressure Thermodynamic Properties of f-electron Metals, Transition Metal Oxides, and Half-Metallic Magnets

Description: This project involves research into the thermodynamic properties of f-electron metals, transition metal oxides, and half-metallic magnets at high pressure. These materials are ones in which the changing importance of electron-electron interactions as the distance between atoms is varied can tune the system through phase transitions from localized to delocalized electrons, from screened to unscreened magnetic moments, and from normal metal to one in which only a single spin specie can conduct. Three main thrusts are being pursued: (i) Mott transitions in transition metal oxides, (ii) magnetism in half-metallic compounds, and (iii) large volume-collapse transitions in f-band metals.
Date: August 2, 2005
Creator: Scalettar, Richard T. & Pickett, Warren E.
Partner: UNT Libraries Government Documents Department

High-Pressure Thermodynamic Properties of f-electron Metals, Transition Metal Oxides, and Half-Metallic Magnets

Description: This project involves research into the thermodynamic properties of f-electron metals, transition metal oxides, and half-metallic magnets at high pressure. These materials are ones in which the changing importance of electron-electron interactions as the distance between atoms is varied can tune the system through phase transitions from localized to delocalized electrons, from screened to unscreened magnetic moments, and from normal metal to one in which only a single spin specie can conduct. Three main thrusts are being pursued: (1) Mott transitions in transition metal oxides, (2) magnetism in half-metallic compounds, and (3) large volume-collapse transitions in f-band metals.
Date: July 1, 2004
Creator: Scalettar, Richard T. & Pickett, Warren E.
Partner: UNT Libraries Government Documents Department

Impact of storage rings on elementary particle physics

Description: It is well known that new experimental discoveries often closely follow the development of new technology. There is hardly a better example of this than the close coupling between new discoveries in the frontiers of elementary particle physics and the development of the art and science of making high-energy accelerators. It is almost twenty-five years since the construction of the Bevatron made possible the discovery of the antiproton; and, since that time, knowledge and understanding of particle physics has made enormous strides in step with new developments in both the accelerator and the detector arts. An attempt is made to document how intimately many of the recent advances have been tied to the success in the development of storage rings and colliding beams.
Date: March 1, 1979
Creator: Trilling, G.H.
Partner: UNT Libraries Government Documents Department

Like-sign charged Higgs boson production in e{sup -}e{sup -} collisions at the NLC

Description: We consider the production of a pair of like-sign charged Higgs bosons in e{sup -} e{sup -} collisions at the NLC within the context of several electroweak models with extended symmetry breaking sectors. We find that the rate for this process, which proceeds through W{sup -}W{sup -} fusion, is a very sensitive probe of the nature of these extended Higgs sectors and that the corresponding cross sections can vary by as much as several orders of magnitude at NLC energies.
Date: October 1, 1995
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Many-body interactions in quasi-freestanding graphene

Description: The Landau-Fermi liquid picture for quasiparticles assumes that charge carriers are dressed by many-body interactions, forming one of the fundamental theories of solids. Whether this picture still holds for a semimetal such as graphene at the neutrality point, i.e., when the chemical potential coincides with the Dirac point energy, is one of the long-standing puzzles in this field. Here we present such a study in quasi-freestanding graphene by using high-resolution angle-resolved photoemission spectroscopy. We see the electron-electron and electron-phonon interactions go through substantial changes when the semimetallic regime is approached, including renormalizations due to strong electron-electron interactions with similarities to marginal Fermi liquid behavior. These findings set a new benchmark in our understanding of many-body physics in graphene and a variety of novel materials with Dirac fermions.
Date: June 3, 2011
Creator: Siegel, David; Park, Cheol-Hwan; Hwang, Choongyu; Deslippe, Jack; Fedorov, Alexei; Louie, Steven et al.
Partner: UNT Libraries Government Documents Department

Physics and technology of the next linear collider

Description: The authors present the prospects for the next generation of high-energy physics experiments with electron-positron colliding beams. This report summarizes the current status of the design and technological basis of a linear collider of center-of-mass energy 0.5--1.5 TeV, and the opportunities for high-energy physics experiments that this machine is expected to open. The physics goals discussed here are: Standard Model processes and simulation; top quark physics; Higgs boson searches and properties; supersymmetry; anomalous gauge boson couplings; strong WW scattering; new gauge bosons and exotic particles; e{sup {minus}}e{sup {minus}}, e{sup {minus}}{gamma}, and {gamma}{gamma} interactions; and precision tests of QCD.
Date: June 1, 1996
Partner: UNT Libraries Government Documents Department

Physics with low-energy e/sup +/e/sup /minus// and e/sup /minus//e/sup /minus// collisions at Tau-Charm Factory

Description: The physics opportunities in e/sup /plus//e/sup /minus// collisions with /radical/s /approx equal/ 1-2 GeV and e/sup /minus//e/sup /minus// collisions with /radical/s /approximately/5 GeV at Tau-Charm Factory are being explored. The low-energy e/sup /plus//e/sup /minus// option allows precise measurements of e/sup /plus//e/sup /minus// cross sections into /pi/'s and /eta/'s and hence stringent tests of the conserved-vector-current (CVC) hypothesis in /tau/ decays. Precise measurement of the total hadronic cross section also permits a more precise calculation of the muon anomalous magnetic moment (g-2). The e/sup /minus//e/sup /minus// option provides an opportunity for a sensitive search for lepton-number violating processes e/sup /minus//e/sup /minus// /yields/ /mu//sup /minus///mu//sup /minus//, /tau//sup /minus///tau//sup /minus//, /mu//sup /minus///tau//sup /minus// .... The e/sup /minus//e/sup /minus// collider also provides an ideal laboratory for two-photon physics with no one-photon background and the direct measurement of the two-photon background in one-photon physics 19 refs., 4 figs.
Date: July 1, 1989
Creator: Gan, K.K.
Partner: UNT Libraries Government Documents Department

Power corrections, renormalons and resummation

Description: I briefly review three topics of recent interest concerning power corrections, renormalons and Sudakov resummation: (a) 1/Q corrections to event shape observables in e(+)e(-) annihilation, (b) power corrections in Drell-Yan production and (c) factorial divergences that arise in resummation of large infrared (Sudakov) logarithms in moment or `real` space.
Date: August 1, 1996
Creator: Beneke, M.
Partner: UNT Libraries Government Documents Department