bluuebunny/crossref_metadata_2025 huggingface dataset:
LATTICE ALGEBRAS AND THE HIDDEN SYMMETRY OF THE 2D ISING MODEL IN A MAGNETIC FIELD
Authors: LEVY DAN
Published: November 2004

Lattice algebras are defined and used to study the symmetries of 2D lattice models. New and interesting examples of such algebras are provided by the affine Hecke algebra, owing to the possibility of constructing braid generators out of its generators. I propose an Ansatz for the braid generators and derive some solutions. A particular finite-dimensional quotient is shown to be a natural generalization of the Temperley-Lieb-Jones algebra. It is used to give a unified picture of known and unknown symmetries of the spin-½ xxz model with boundary terms. The Ising model in an external magnetic field is also a representation of this quotient.
INTEGRABILITY OF OPEN SPIN CHAINS WITH QUANTUM ALGEBRA SYMMETRY
Authors: MEZINCESCU LUCA , NEPOMECHIE RAFAEL I.
Published: November 2004

We construct an open quantum spin chain from the “twisted” [Formula: see text]R matrix in the fundamental representation which has the quantum algebra symmetry Uq[ su (2)]. This anisotropic spin-1 chain is different from the Uq[ su (2)]-invariant chain constructed from the “untwisted” [Formula: see text] spin-1 R matrix (namely, the spin-1 XXZ chain of Fateev-Zamolodchikov with boundary terms) but, nevertheless, is also completely integrable. We discuss the general case of an R matrix of the type g(k), where k∈{1, 2, 3}, and g is any simple Lie algebra.
COHERENCE AND INCOHERENCE IN THE PHOTON AND DILEPTON PRODUCTION BY BREMSSTRAHLUNG IN RELATIVISTIC HEAVY-ION COLLISIONS
Authors: LIPPERT THOMAS , THIEL JOACHIM , GRÜN NORBERT , SCHEID WERNER
Published: November 2004

Due to the strong collective deceleration during the initial stage of relativistic heavy-ion collisions, the nuclear matter irradiates real and virtual bremsstrahlung. We describe the process of bremsstrahlung emission in the framework of a semiclassical model in order to study coherence and incoherence effects in the production process. Guided by the intuitive notation of shock fronts being formed between the incident nuclei, we use a simple parametrization of the nuclear current density. The photon spectrum is studied up to photon energies of 300 MeV. In particular, a gradual transition from the coherent production process of low-energy photons to the incoherent one for hard photons is demonstrated. For heavy collision systems coherence effects in the photon spectra dominate, showing characteristic structures arising from shock fronts. The dilepton spectrum is described in first-order perturbation theory. Generally, dileptons are found to be produced incoherently. Only in the case of dielectron production with small invariant pair masses do moderate coherence effects survive.
Application of the Landau-Luttinger Liquid Formulation to the Study of the Magnetic Properties of the 1-D Hubbard Model
Authors: Carmelo J. , Horsch P. , Bares P.A. , Ovchinnikov A.A.
Published: November 2004

The Landau-Luttinger liquid formulation is used to investigate the physics of the one-dimensional Hubbard model in a magnetic field of arbitrary strength H. The low lying charge and spin excitations are studied. A novel branch of sound wave-like spin excitations arises for H>0. The low temperature thermodynamics is considered in some detail.
CORRELATION FUNCTIONS IN ONE-DIMENSIONAL LARGE-U HUBBARD MODEL: ZERO-FIELD AND FINITE-FIELD CASES
Authors: SHIBA Hiroyuki , OGATA Masao
Published: November 2004

A recent study of the large-U limit of the one-dimensional (1D) Hubbard model is presented and discussed. It is pointed out first that the wave function has a simple structure in this limit. Namely, it is a product of Slater determinant of noninteracting spinless fermions and the wave function of 1D S=1/2 Heisenberg antiferromagnet. Secondly, by using this property, a direct calculation of momentum distribution and spin correlation function is carried out for the ground state at zero-field and finite-field cases. The results show various singularities exactly at the same position where one expects for the small-U case in both zero-field and finite-field cases. The critical exponents estimated from the size dependence are in reasonable agreement with those predicted by the Tomonaga-Luttinger-liquid and the conformal field theory.
NUMERICAL STUDIES OF STRONGLY CORRELATED ELECTRONIC MODELS
Authors: Dagotto Elbio
Published: November 2004

Recent numerical work on strongly correlated electronic models using the Lanczos approach is reviewed. In particular static and dynamical properties of the Hubbard, t—J (with one, two and more holes) and the spin-½ Heisenberg antiferromagnet are presented. An attempt to summarize the current active search for nontrivial ground states of the frustrated Heisenberg model is made. Numerical methods like the Lanczos technique are providing useful information in the study of these models.
HARD-CORE SLAVE-BOSON DESCRIPTION OF GENERALIZED FLUX PHASES
Authors: Nori Franco , Zimanyi Gergely T. , Abrahams Elihu
Published: November 2004

Through a hard-core slave-boson mean-field approach to the t-J model, which describes the dynamics of holes moving in a quantum antiferromagnet, we investigate its generalized flux phases. We first study the motion of an electron gas for arbitrary fillings and fields and establish the linear proportionality between the filling factor and the optimal flux with high accuracy. Using this result, we show that if the hard-core nature of the hole bosons is taken into account, then the slave-boson mean-field approximation for the t-J Hamiltonian allows for a solution where both the spinons and the holons experience an average flux of one flux quantum per particle. This enables them to achieve the lowest possible energy within the manifold of spatially-uniform flux states. In the case of the continuum model, this is possible only for certain fractional fillings and we suggest that the system may react to this frustration effect by phase separation.
A single hole in a quantum antiferromagnet: selfconsistent Green’s function approach
Authors: Martínez Gerardo , Horsch Peter
Published: November 2004

We solved numerically the integral equation for the selfenergy which describes the motion of a single hole in a two-dimensional quantum antiferromagnet (AF) within the selfconsistent Born approximation. This formulation stresses the similarity of the AF-spin polaron with the standard polaron problem. We confine our calculation to finite cluster geometries and compare with results from previous exact diagonalization studies. The spectral function is characterized by a narrow quasiparticle (qp) peak at the low energy side of the spectra, which appears to be well separated from the incoherent band part for large enough J values. For small J we find a reduced width of ~7t for the incoherent band. The bottom of the coherent qp band always occurs at (±π/2, ±π/2). Its bandwidth initially increases with J until J≃t and then decreases as 2t2/J. A complete characterization of our solution is given, including the dispersion relation and effective masses of this quasiparticle. The comparison with exact diagonalization studies for a 4×4 cluster is remarkably good. From our results we see that a lattice of 16×16 sites describes adequately the thermodynamic limit. We conclude that the simple Born approximation is a valuable scheme to characterize the dynamics of one hole in the t-J model. both in the perturbative and the strong coupling regimes.
MODELS OF CORRELATED FERMIONS IN THE SLAVE BOSON APPROXIMATION FOR THE COPPER OXIDE SYSTEMS
Authors: Entel P. , Behera S.N. , Zielinski J. , Kaufmann E.
Published: November 2004

In this short communication we discuss results obtained for the single and multi-orbital Hubbard models within the mean-field-slave-boson description of correlated fermions on a square lattice. For appropriate parameter values the results can be used to mimic some of the normal state properties of the copper oxide systems. Results for the single and multi-orbital models differ in a very characteristic manner. In the single band case the phase diagram consists of metallic (UUc) regions, which are clearly seperated at half filling (Uc being the critical value of the Brinkman-Rice transition1)). Upon doping the transition between these two phases smoothes out and for large enough doping (δ>0.2, δ=1−n) the system behaves as a weakly correlated metal. In the multi-oibital case depending on the input energies for the orbitals the transition to the insulating state can be either of the Brinkman-Rice or the charge-transfer type. Similar to the single band case doping causes rapid loss of correlation effects. We tentatively conclude that the Kondo-type of effect is absent in the multi-orbital model.
FRUSTRATED SPIN (J-J') SYSTEMS DO NOT MODEL THE MAGNETIC PROPERTIES OF HIGH-TEMPERATURE SUPERCONDUCTORS
Authors: Bacci Silvia , Gagliano Eduardo , Nori Franco
Published: November 2004

We study the t—J model with one hole and the frustrated Heisenberg J—J′ model in a square lattice. Specifically, we compute and compare for both, the doped and frustrated models, the dynamic spin-spin structure factor S(q, ω), and the B1g Raman scattering spectrum R(ω) at zero temperature. The behavior of these quantities differs between the t—J and the J—J′ models. We observe that both the B1g Raman spectrum as well as the structure factor for the t—J model are in qualitative agreement with experimental measurements while the corresponding results for the J—J′ model are not. These results indicate that the magnetic behavior of doped systems cannot be accurately modeled by a purely spin Hamiltonian. These results are of relevance to the claim that the effect of adding holes (doping) on the magnetic properties of the quantum Heisenberg antiferromagnet can be described by introducing second and sometimes third nearest-neighbor couplings, J′ and J″ respectively, in the original (undoped) Hamiltonian.
Charge-Vortex Binding, Fractional Quantum-Hall Effect and Anyon Superconductivity
Authors: Lee Dung-Hai
Published: November 2004

I review the concept of statistics transmutation in two dimensions and apply it to the understanding of Fractional quantum-Hall effect and anyon superconductivity. The relevance of the anyon model to copper-oxide superconductors is also discussed.
COLLECTIVE FIELD THEORY APPLIED TO THE FRACTIONAL QUANTUM HALL EFFECT
Authors: Sakita B. , Sheng Dong-Ning , Su Zhao-Bin
Published: November 2004

We present an application of collective field theory to the fractional quantum Hall effect (FQHE). We first express the condition, that the electrons are all in the lowest Landau level, as a constraint equation for the state functional. We then derive the fractional filling factor from this equation together with the no-free-vortex assumption. A hierarchy of filling factors is derived by using the particle-vortex dual transformations. In the final section we discuss an attempt at a dynamical theory of FQHE, which would justify the no-free-vortex assumption. A derivation of Laughlin’s wave function with and without quasi-hole excitations is also given.
STABILITY OF ISING SYSTEMS AGAINST NON-HAMILTONIAN, SYMMETRY BREAKING DYNAMICS
Authors: BLÖTE H.W.J. , HERINGA J.R. , HOOGLAND A. , ZIA R.K.P.
Published: November 2004

We investigate two-dimensional Ising models with a non-Hamiltonian Glauber dynamics. The transition probabilities are expressed in terms of Boltzmann factors depending only on the nearest neighbour spins and the associated bond strengths. However, the bond strength on each lattice edge is two-valued; it assumes different values with respect to the spins at either of its ends. In one of the two models, the bond strength pattern is consistent with the four-fold rotational symmetry of the square lattice. In contrast, a preferred direction is present in the second model. This model can be interpreted in terms of inhomogeneous interactions and temperature such that their ratios, i. e. the couplings, are uniform. Monte Carlo simulations of these models show that the phase transition persists when these two types of non-Hamiltonian dynamics are introduced. Furthermore, our results indicate that both models belong to the Ising universality class.
FIRST ORDER METAL-INSULATOR TRANSITION IN AN ALLOY ANALOGY APPROACH TO THE HUBBARD MODEL
Authors: CORRIAS MASSIMO
Published: November 2004

The self-consistent coherent potential approximation introduced in Ref. 3 is extended to the hopping part of the Hubbard Hamiltonian in an alloy analogy scheme. There results the renormalization of the unperturbed bandwidth w by the appearance of a spin and potential strength dependent factor Φσ(u), the latter leads — in the magnetically disordered case, at electron densities n not far from 1, for small values of the temperature k B T with respect to w and values of u smaller than those needed to cause the Hubbard splitting — to a first order metal-insulator transition: Φ and the double occupancy probability D undergo a sudden drop. It is also shown that in the approximation proposed the system becomes strongly ferromagnetic in the thermodynamic limit at n = 1 and T = 0 if u is sufficiently large.
NONBOSON TREATMENT OF EXCITONIC NONLINEARITY IN OPTICALLY EXCITED MEDIA
Authors: NGUYEN BA AN
Published: November 2004

The present article shortly reviews some recent results in the study of excitonic nonlinearity in optically excited media using a nonboson treatment for many-exciton systems. After a brief discussion of the exciton nonbosonity the closed commutation relations are given for exciton operators which hold for any exciton density and type. The nonboson treatment is then applied to the problems of intrinsic optical bistability and nonlinear polariton yielding quite interesting and new effects, e.g. new shapes of hysteresis loops of intrinsic optical bistability or anomalies of polariton dispersion.
LASER ZEEMAN AND NMR SPECTROSCOPY: EFFECTIVE TORQUE AND LASER LARMOR PRECESSION
Authors: EVANS M. W.
Published: November 2004

Laser Zeeman effects are caused by optical rectification in an electromagnetic field, in close formal analogy with the well known effects of static magnetic flux density (B). The conjugate product (Π) and dynamic molecular polarisability vector (iα″) form a torque formally analogous to that between the molecular magnetic dipole moment (m) and B. This defines the Larmor frequency of precession, which is shown to be directly proportional to the square of the electric field strength (E0, in volt m −1) of the laser through a molecular constant analogous to the gyromagnetic ratio. Supercomputer simulation is used to show that this torque generates distinctive new ensemble averages (time cross correlation functions) which mediate the onset of circular birefringence and dichroism ("magnetic" optical activity). Resonance in the presence of a co-axial magnetic field leads to "laser NMR" effects, which are created simply in terms of the torque and Larmor precession.
FERMION INDUCED SINGULARITIES IN A NON-RELATIVISTIC EFFECTIVE LAGRANGIAN FOR ELECTROMAGNETISM
Authors: RANDJBAR-DAEMI S. , SALAM ABDUS , STRATHDEE J.
Published: November 2004

Effective field theory methods are applied to the study of non-relativistic quantum electrodynamics in a slowly varying electromagnetic background. It is shown that the one-loop effective action has singularities at those values of the background fields which correspond to complete fillings of Landau levels. One immediate result of our work is a simple derivation of the oscillatory behaviour of the energy density magnetization and permittivities, at zero temperature.
MECHANISMS AND ENERGETICS OF SURFACE ATOMIC PROCESSES, AN ATOM-PROBE FIELD ION MICROSCOPE STUDY
Authors: TSONG TIEN T.
Published: November 2004

The energies involved in various surface atomic processes such as surface diffusion, the binding of small atomic clusters on the surface, the interaction between two adsorbed atoms, the dissociation of an atom from a small cluster or from a surface layer, the binding of kink site atoms or atoms at different adsorption sites to the surface etc., can be derived from an analysis of atomically resolved field ion microscope images and a kinetic energy measurement of low temperature field desorbed ions using the time-of-flight atom-probe field ion microscope. These energies can be used to compare with theories and to understand the transport of atoms on the surface in atomic reconstructions, epitaxial growth of surface layers and crystal growth, adsorption layer superstructure formation, and also why an atomic ordering or atomic reconstruction at the surface is energetically favored. Mechanisms of some of the surface atomic processes are also clarified from these quantitative, atomic resolution studies. Very recent work in this area is briefly reviewed.
VAN HOVE SINGULARITIES AND HIGH-Tc SUPERCONDUCTIVITY: A REVIEW
Authors: MARKIEWICZ R. S.
Published: November 2004

This review describes a Fermi liquid picture of high-T c superconductivity. A density-of-states (dos) peak associated with the CuO 2-plane van Hove singularity causes a peak in T c as a function of hole doping. Strong correlation effects drive a Mott transition at half filling. For intermediate doping, the electronic system is unstable against phase separation, with one phase near the insulating state, the other near the T c peak.

The large dos leads to competition between superconductivity and structural instability, in analogy with the A15 compounds. The superconductivity appears to be driven by strong electron-phonon coupling, enhanced by fluctuation effects.
INTERACTION BETWEEN O QUASIPARTICLES IN CuO2-BASED SUPERCONDUCTORS
Authors: ALIGIA A. A.
Published: November 2004

We consider the extended Hubbard model including repulsion Upd between nearest-neighbor Cu and O holes. In the limit of strong intra-atomic correlations and weak hopping, we derive an effective Hamiltonian for the O holes. This Hamiltonian contains interactions between O holes with a common nearest-neighbor Cu ion. The effective interaction between two holes is repulsive for small Upd and attractive otherwise. Bound states between two holes exist only if the effective interaction between them is sufficiently large and negative.
RIGOROUS RESULTS ON THE ANISOTROPIC TRIANGULAR ISING MODEL
Authors: LIN K. Y. , WU F. Y.
Published: November 2004

We consider the Ising model on the triangular lattice with anisotropic pair interactions, staggered triplet interactions, and an external magnetic field. Using the Yang-Lee zero consideration and a star-triangle transformation which eliminates the triplet interactions, we obtain regimes in the parameter space which are free of phase transitions.
INFLUENCE OF TWIST DISTORTION ON THE TRANSITION POINT BETWEEN TWO NEMATIC SUBPHASES N1 AND N2 OF HOBA
Authors: BARBERO G. , KOMITOV L. , PETROV M. , STRIGAZZI A.
Published: November 2004

The liquid crystal HOBA exhibits a nematic phase between the achiral smectic C region and the isotropic one. In the nematic phase two subphases N1 and N2 can be distinguished. A shift of the transition temperature N1 − N2 has been observed, if an elastic deformation is involved, with respect to the unidirectional homogeneous case. In the present paper the experimental data concerning a twist distortion are discussed, and a theoretical model is given.
QUANTUM STEADY COMPUTATION
Authors: CASTAGNOLI GIUSEPPE
Published: November 2004

Current conceptions of "quantum mechanical computers" inherit from conventional digital machines two apparently interacting features, machine imperfection and temporal development of the computational process. On account of machine imperfection, the process would become ideally reversible only in the limiting case of zero speed. Therefore the process is irreversible in practice and cannot be considered to be a fundamental quantum one.

By giving up classical features and using a linear, reversible and non-sequential representation of the computational process — not realizable in classical machines — the process can be identified with the mathematical form of a quantum steady state. This form of steady quantum computation would seem to have an important bearing on the notion of cognition.
BOGOLUBOV’S HIERARCHIES AND VLASOV’S EQUATIONS IN POPULATION ECOLOGY
Authors: PAVLOTSKY I.P. , SUSLIN V.M.
Published: November 2004

Following Bogolubov’s ideas a system of pseudo-differential equations for the density functions of interacting biological species is constructed in self-consistent Vlasov’s approximation. Some mathematical properties of these equations including the Cauchy problem are obtained in the particular case of Volterra’s dynamics. For this case we propose a method of numerical calculation of the evolution of the density functions. Some examples of the numerical solutions are given.
THE DIFFEOMORPHISM GROUP APPROACH TO ANYONS
Authors: GOLDIN GERALD A. , SHARP DAVID H.
Published: November 2004

We explain an approach to quantum mechanics, based on diffeomorphism groups and local current algebras, that predicts many of the fundamental properties of anyons. Our formulation also yields further insight into the meaning of particle statistics, and permits the unified description of a wide variety of quantum systems.
NONLINEAR WAVE PROPAGATION IN DISORDERED MEDIA
Authors: SÁNCHEZ ANGEL , VÁZQUEZ LUIS
Published: November 2004

We briefly review the state-of-the-art of research on nonlinear wave propagation in disordered media. The paper is intended to provide the non-specialist reader with a flavor of this active field of physics. Firstly, a general introduction to the subject is made. We describe the basic models and the ways to study disorder in connection with them. Secondly, analytical and numerical techniques suitable for this purpose are outlined. We summarize their features and comment on their respective advantages, drawbacks and applicability conditions. Thirdly, the Nonlinear Klein-Gordon and Schrödinger equations are chosen as specific examples. We collect a number of results that are representative of the phenomena arising from the competition between nonlinearity and disorder. The review is concluded with some remarks on open questions, main current trends and possible further developments.
LOCALIZATION OF SOLITONS IN DISORDERED MATERIALS
Authors: ABDALLA S. , OSMAN EL-SAYED
Published: November 2004

Starting with the usual sine-Gordon equation in the presence of weak external perturbations, we have shown that solitons are localized inside potential barriers of Schottky type. These barriers are due to the disorder effect in the material. The case is examined in both static (t=0) and dynamic barriers for only low-velocity solitons. Localization of solitons reduces their velocity and affects its centre-of-mass.
GENERALIZED COHERENT STATES FOR DYNAMICAL SUPERALGEBRAS
Authors: PELIZZOLA ALESSANDRO , TOPI CORRADO
Published: November 2004

Coherent states for a general Lie superalgebra are defined following the method originally proposed by Perelomov. Algebraic and geometrical properties of the systems of states thus obtained are examined, with particular attention to the possibility of defining a Kähler structure over the states supermanifold and to the connection between this supermanifold and the coadjoint orbits of the dynamical supergroup. The theory is then applied to some compact forms of contragradient Lie superalgebras.
EXPERIMENTAL CONSTRAINTS ON BOSON-EXCHANGE MECHANISMS FOR HIGH Tc SUPERCONDUCTORS
Authors: COHEN MARVIN L.
Published: November 2004

At this point there is no consensus on which of the proposed theories best explains the properties of the high T c oxides. In addition to anyon theories, there are variations on the more conventional boson-exchange pairing mechanisms which have been suggested. Analyses of experimental data such as the isotope effect, gap to T c ratio, and heat capacity discontinuity at T c put constraints on the applicability of these theories and limit the number of acceptable proposals.
LONG DISTANCE PHYSICS OF THE HALL FLUID AND THE ANYON SUPERFLUID
Authors: ZEE A.
Published: November 2004

The long distance physics of the Hall fluid and the anyon superfluid may be described by effective field theories constructed out of the Chern-Simons term. These theories are topological in character and may be of deep mathematical significance. Various physical quantities such as the quantum numbers of the quasiparticles are determined by a matrix appearing in the Chern-Simons term.
ANYONS IN A MAGNETIC FIELD: LANDAU LEVELS AND VERTEX OPERATOR REPRESENTATION
Authors: Dunne Gerald V. , Lerda Alberto , Trugenberger Carlo A.
Published: November 2004

We construct exact many-body eigenstates of both energy and angular momentum for the N-anyon problem in an external magnetic field. Such states span the full ground-state eigenspace and have a natural representation in terms of the Fubini-Veneziano vertex operators of string theory.
Aharonov-Bohm and Statistical Phases in the Fractional Quantum Hall Effect
Authors: Su W. P.
Published: November 2004

The ν=1/q quantum Hall states are characterized by a perfect cancellation of the magnetic (Aharonov-Bohm) and the Fermi statistical phases. The lowering of the ground state energy due to this phase cancellation is illustrated by using a partial analogy with the Helium II problem and via a path integral formulation. For general filling fractions ν=p/q, a cluster of p electrons is considered instead of a single electron. There is again a perfect cancellation of the effective Aharonov-Bohm phase and the statistical phase of the clusters provided that q is odd.
NON-1/m FRACTIONAL QUANTUM HALL EFFECT IS A MANIFESTATION OF ANYON SUPERCONDUCTIVITY
Authors: Hu Chia-Ren
Published: November 2004

Regarding electrons as anyons of index αs pierced with -(m+αs) flux quanta per particle, and letting the mean field of these fluxes cancel the external magnetic field B, we obtain the filling factor ν=1/(m+αs), where m must be odd. Demanding the resulting system of anyons to exhibit "anyon supercanductivity", we obtain αs=±(1-q/n) where q is odd, and n>q is relatively prime to q. For q=1 we recover a formula due to Jain, and resolve the mystery why, for a state with ν=n/(2pn±1)<1 he requires use of the statistical correlation of n filled Landau levels. For q=3,5,⋯, we obtain the fractions 4/11, 4/13, 5/13, etc., which are missing from Jain's list. Thus this non-heirarchical approach to the non-1/m fractional quantum Hall effect has the strengths of Jain's composite-fermion approach, but not its (potential) weaknesses.
One-dimensional Large-U Hubbard Model in Strong Coupling: Charge and Spin Separation
Authors: Weng Z. Y. , Sheng D. N. , Ting C. S.
Published: November 2004

A path-integral formalism of the Hubbard model is used to study the one-dimensional large-U case. It is shown that the bare electron (hole) becomes a composite particle of two decoupled excitations, holon and spinon, together with the non-local string fields. Various correlation functions are analytically derived. The results strongly suggest a U*=∞ fixed point of Hubbard model which is distinct from the weak coupling case.
SQUEEZED STATE OF BIEXCITONS IN EXCITED SEMICONDUCTORS
Authors: AN NGUYEN BA
Published: November 2004

Exact time-evolution is analytically derived from a coherent photon-exciton system subjected to a monochromatic radiation field resonant with the exciton-biexciton transition. It is shown that biexcitons, which appear under the resonant pumping, might periodically behave as squeezed quasiparticles, if photons or/and excitons are initially in squeezed states. The squeezing degree of the initial photons or/and excitons, the pumping intensity and the off-resonance detuning are demonstrated to govern the transfer of squeezing from the photon-exciton system to the biexciton.
De Haas-Van Alphen and Shubnikov-De Haas Oscillations in Strongly Correlated Electron Gas
Authors: Rodriguez J.P. , Lederer Pascal
Published: November 2004

We investigate the de Haas van Alphen (dHvA) and Shubnikov-de Haas (SdH) oscillations in a 2D strongly correlated electron system. The normal state is described by the fluxless phase (uniform RVB) of the t−J model. In the quantum limit, we find that conventional 2D dHvA sawtooth behavior is unattainable: in the limit near half-filling, where the magnetic energy dominates, one has square wave dHvA behavior with reduced amplitude; far from half-filling one finds a mixed square wave-sawtooth regime. The dHvA oscillation frequency is unchanged in all regimes, and it corresponds to Luttinger’s Fermi surface. A conventional SdH effect exists in the above mentioned conventional regime, whereas it is absent in the square-wave dHvA regime. Lastly, it is shown that the linear-in-T contribution to the resistivity arising from chiral fluctuations in the fluxless phase dissappears in the presence of magnetic field in the quantum limit. We therefore predict that this strongly correlated metal shows a large negative magneto-resistance.
MONTE CARLO STUDY OF ONE HOLE IN A QUANTUM ANTIFERROMAGNET
Authors: Sorella S.
Published: November 2004

Using the standard Quantum Monte Carlo technique for the Hubbard model, I present here a numerical investigation of the hole propagation in a Quantum Antiferromagnet. The calculation is very well stabilized, using selected sized systems and special use of the trial wavefunction that satisfy the “close shell condition” in presence of an arbitrarily weak Zeeman magnetic field, vanishing in the thermodynamic limit. It will be shown in a forthcoming publication1 that the presence of this magnetic field does not affect thermodynamic properties for the half filled system. Then I have used the same selected sizes for the one hole ground state. I have investigated the question of vanishing or nonvanishing quasiparticle weight, in order to clarify whether the Mott insulator should behave just as conventional insulator with an upper and lower Hubbard band. By comparing the present finite size scaling with several techniques predicting a finite quasiparticle weight (see Fig.1) the data seem more consistent with a vanishing quasiparticle weight, i.e. , as recently suggested by P.W. Anderson2 the Hubbard-Mott insulator should be characterized by non-trivial excitations which cannot be interpreted in a simple quasi-particle picture. However it cannot be excluded , based only on numerical grounds, that a very small but non vanishing quasiparticle weight should survive in the thermodynamic limit.
Balance-Equation Approach to Hot-Carrier Transport in Semiconductors
Authors: Lei X.L. , Horing N.J.M.
Published: November 2004

The balance-equation approach to nonlinear hot-carrier transport theory, formulated by Lei and Ting (1984), is addressed in this comprehensive review. A central feature is the role of strong electron-electron interactions in promoting rapid thermalization about the drifted transport state and the concomitant substantial simplification of the transport theory. This physical feature is embodied in the initial density matrix chosen to represent the unperturbed carrier system.

Force and energy balance equations are formulated for the dc steady state, ac dynamic and transient cases of charge conduction, including memory effects. The scattering mechanisms include impurity and phonon interactions along with dynamic nonlocal screening effects due to carrier-carrier interactions. Both linear and nonlinear resistivities are discussed in the degenerate and nondegenerate statistical regimes. Interesting phenomena such as electron cooling and thermal noise and diffusion are discussed as well.

Semiconductor microstructure transport is described for both linear and nonlinear hot carrier conduction. In this connection, quasi-2D-systems, heterojunctions, and quantum well superlattices are treated with attention to steady state, transient and high frequency transport, including, for example, superlattice plasmon resonance structure. Type-II superlattice transport is reviewed as well as type-I, and electron-hole drag is treated in conjunction with negative minority electron mobility in a quantum well. Multivalley semiconductors are discussed in some detail. Furthermore, attention is also focused on the center-of-mass velocity fluctuation, Langevin-type equation and thermal noise and diffusion for microstructures and multivalley systems. A number of particularly important phenomena are examined from the balance-equation point of view, such as nonequilibrium phonons, higher order scattering effects and weak localization, hydrodynamic equations for weakly nonuniform systems, and the intracollisional field effect.

Alternative formulations and interpretations of the balance-equation approach are reviewed. The distinction between this many-particle, isothermal, balance-equation theory and the noninteracting (single-particle) adiabatic transport theory is discussed to clarify issues subject to controversy in the literature. Finally, we give a brief review of recent developments in the balance-equation approach: investigation of the distribution function in balance-equation theory, improved calculations for GaAs/AlGaAs heterojunctions, extension of the balance equations to an abitrary energy band and recent work on superlattice miniband transport.
Recent Developments in Magnetotransport Theory
Authors: Horing Norman J.M. , Cui H.L. , Lei X.L.
Published: November 2004

A selection of topics recently examined in the literature of normal, dissipative magnetotransport is reviewed here, principally from the perspective of the Lei-Ting balance equation approach. We employ this isothermal formalism to revisit linear and nonlinear bulk 3D magnetoresistance, discussing longitudinal impurity limited conduction and magnetophonon resonance structure. For the transverse configuration, the characteristic linear impurity magnetoresistance log-divergence is seen to be removed by nonlinearity alone, with or without screening. At high magnetic fields, prominent hot-electron magnetophonon resonance structure is discussed for transverse transport as well as thermal noise. Another principal focus of concern here is the role of Landau quantization in linear and nonlinear transport in semiconductor microstructures, particularly quantum well superlattices (Type-I and Type-II) and heterostructures, including magnetoplasmon and cyclotron resonances as well as Shubnikov-de Haas oscillations. Electron-hole drag and negative absolute minority carrier mobility are discussed. Finally, we briefly discuss the density modulated 2DEG having magnetoresistance commensurability oscillations due to the interplay of the length scales of the cyclotron radius and the modulation period (superposed as an envelope upon Shubnikov-de Haas oscillations).
NONLINEAR TRANSPORT OF ELECTRONS UNDER A STRONG HIGH FREQUENCY ELECTRIC FIELD IN SEMICONDUCTORS
Authors: Cai W. , Lax M.
Published: November 2004

The nonlinear transport of electrons in semiconductors is studied when a strong high frequency (HF) electric field is applied together with a direct current (dc) electric field. A set of equations is developed, from which the amplitude and phase of each harmonic component of the electron drift velocity and the electron temperature can be computed. In the weak HF field limit our approach reduces to the well-known memory function method. The DC conductivity decreases and definitely becomes negative with increase of the first and second harmonic components of the applied HF field. Comparison is made with experiment.
FORMATION OF THE CHARGE DENSITY WAVES IN THE β-TYPE OXIDE VANADIUM BRONZES NaxV2O5
Authors: DMITRIEV A.V. , ZHURAVLEV N.A. , VOLKOV V.L.
Published: November 2004

NMR of 51 V and 27 Na in monocrystals β- Na x V 2O5(x=0.22, 0.27, 0.33) has been studied between 80 K and 400 K. Temperature dependences of hyperfine interactions have been investigated. In all compositions under study, a phase transition has been observed, its temperature has decreased with a reducing natrium content. A joint analysis of magnetic susceptibilities and resonance shifts showed that the phase transition has been connected with a gap formation at the Fermi level. Investigations of quadrupole effects and electroconductivities allowed to establish that the phase transition has been accompanied by a charge density wave development. On the basis of NMR measurements, an electron localization region has been evaluated. The results have been compared with electrophysical data.
WZW QUANTUM DIMENSIONS
Authors: FUCHS JÜRGEN
Published: November 2004

Some aspects of quantum dimensions of primary fields of WZW theories are described. Quantum dimensions are an important tool in the analysis of the fusion rules, both for the description of general properties and for actual calculations. A complete list of WZW primaries having quantum dimension not larger than two is presented. An amazing connection between the presence of such fields and the value of the conformal central charge emerges.
A CONSTRUCTIVE QUANTUM FIELD THEORETIC APPROACH TO CHERN-SIMONS THEORY
Authors: NILL FLORIAN
Published: November 2004

Chern-Simons theory is formulated quantum field theoretically in terms of string operators, which are localized on finite non-selfintersecting paths in the zero-time plane R2. It is shown how the Weyl algebra approach to the abelian Chern-Simons theory leads to a bundle theoretic construction of these ‘Chern-Simons string operators’. To proceed to the non-abelian case topological Chern-Simons theory is considered as a specific model of a more general theory describing the quantum kinematics of coloured framed Plek ton s inR2. This theory allows the construction of string operators as pair-creation operators, mapping n-Plekton states into (n+2)-Plekton states. Link invariants are obtained as vacuum correlation functions of string operators and obey a natural version of reflection positivity. The vacuum sector of such a purely kinematical Plekton theory may be recovered from the link invariants by Osterwalder-Schrader reconstruction. To make the theory work one needs the structures of a ribbon graph category, for which the representations of a quasi-triangular quasi-Hopf algebra may serve as a specific realization.
GAUGE INVARIANCE IN NON-RELATIVISTIC MANY-BODY THEORY
Authors: FRÖHLICH J. , STUDER U.M.
Published: November 2004

We review some recent results on the physics of two-dimensional, incompressible electron and spin liquids. These results follow from Ward identities reflecting the U(1) em × SU(2) spin -gauge invariance of non-relativistic quantum mechanics. They describe a variety of generalized quantized Hall effects.
COLLECTIVE PHENOMENA IN THE QUANTUM HALL EFFECT
Authors: FERRARI R.
Published: November 2004

The main phenomenological features of Integer Quantum Hall Effect (IQHE) and Fractional Quantum Hall Effect (FQHE) are reviewed. A theory is proposed based on a new basis for the single particle states, given by a representation of the Magnetic Translation Group (MTG).
BILINEAR ANALYSIS OF SHORT-RANGE ORDER IN METALLIC SOLID SOLUTIONS
Authors: MAHMOOD AKHTAR , KHWAJA FARID A.
Published: November 2004

Short-range order parameters and short-range order dependent diffuse intensities are calculated using bilinear analysis in Cu 72 Au 28, Ni-Al and Ni 3 Fe systems. The appearance of short-range order in alloys, quenched from below and above the critical temperature, is also studied using this method. The short-range order parameters calculated in this approach are found to be in agreement with the values determined from volume analysis. Nevertheless, the results of numerical calculation indicate that these parameters can be accurately determined only up to eight coordination shells using the intensity data measured along two lines in the reciprocal space.
AMPLITUDE-SQUARED SQUEEZING IN THE m-PHOTON JAYNES-CUMMINGS MODEL WITH SQUEEZED FIELD INPUT
Authors: MIR MUBEEN A. , RAZMI M.S.K.
Published: November 2004

Amplitude-squared (AS) squeezing has been investigated for the m-photon Jaynes-Cummings model assuming the field to be initially in the squeezed states. The role played by intensity-dependent coupling has also been discussed. It has been shown that for the large initial average photon number [Formula: see text] with odd values of m, AS squeezing revokes permanently whereas with even values it recurs periodically. As m increases the revocation is hastened and the duration of occurrence decreases. Higher values of m for the initial field in a squeezed vacuum state can make one of the quadrature permanently squeezed. The AS squeezing behavior for two initial states of the atom, i.e., ground state versus excited state is also compared.
THE EFFECTS OF VARIOUS DIELECTRIC OILS AND VOLUME FRACTION OF SOLIDS ON THE MECHANICAL PROPERTIES OF HYDROUS BASED ELECTRORHEOLOGICAL FLUIDS
Authors: SPRECHER A. F. , CHEN Y. , CHOI Y. , CONRAD H.
Published: November 2004

Electrorheological (ER) fluids consist of fine polarizable particles suspended in a dielectric liquid. It is the dielectric mismatch between these phases that give rise to the ER effect. This paper presents data on ER fluids with different dielectric oils employing a constant solid phase consisting of zeolite with adsorbed water. The effect of solid concentration was also studied, in order to develop a more complete understanding of the mechanisms involved. Results are explained in terms of the dielectric properties of the phases present using an electrostatic model developed by the authors and an additional structural feature termed as chain bundling. The electrostatic model takes into account the characteristic chain-like structure which is commonly observed in these fluids, while the chain bundling concept incorporates multiple chain interactions.
NUCLEAR MAGNETOHYDRODYNAMIC EMP, SOLAR STORMS, AND SUBSTORMS
Authors: RABINOWITZ MARIO , MELIOPOULOS A.P. SAKIS , GLYTSIS ELIAS N. , COKKINIDES GEORGE J.
Published: November 2004

In addition to a fast electromagnetic pulse (EMP), a high altitude nuclear burst produces a relatively slow magnetohydrodynamic EMP (MHD EMP), whose effects are like those from solar storm geomagnetically induced currents (SS-GIC). The MHD EMP electric field E≲10−1 V/m and lasts ≲102 sec , whereas for solar storms E≳10−2 V/m and lasts ≳103 sec . Although the solar storm electric field is lower than MHD EMP, the solar storm effects are generally greater due to their much longer duration. Substorms produce much smaller effects than SS-GIC, but occur much more frequently. This paper describes the physics of such geomagnetic disturbances and analyzes their effects.
MAGNETIC GROUP ON THE PSEUDOSPHERE
Authors: BARONE V. , PENNA V. , SODANO P.
Published: November 2004

The quantum mechanics of a particle moving on a pseudosphere under the action of a constant magnetic field is studied from an algebraic point of view. The magnetic group on the pseudosphere is SU(1, 1). The Hilbert space for the discrete part of the spectrum is investigated. The eigenstates of the non-compact operators (the hyperbolic magnetic translators) are constructed and shown to be expressible as continuous superpositions of coherent states. The planar limit of both the algebra and the eigenstates is analyzed. Some possible applications are briefly outlined.
STRUCTURE, DYNAMICS, AND FORMATION OF CARBON AND ALUMINUM CLUSTERS
Authors: Zhang Q.-M. , Yi J.-Y , Brabec C.J. , Anderson E.B. , Davidson B.N. , Kajihara S.A. , Bernholc J.
Published: November 2004

The results of recent ab initio molecular dynamics studies of C and Al clusters are presented. The simulations have shown that C 60 molecular structure is well preserved in the solid and that the individual C 60 molecules start to rotate at relatively low temperatures. Our results are in very good agreement with NMR, photoemission, and neutron scattering data. At high temperatures C 60 undergoes large amplitude soccerball-rugbyball oscillations, but the cage structure is still preserved. The C 60 isomer containing two pairs of adjacent pentagons has a binding energy only 1.6 eV smaller than that of perfect C 60, but high temperatures and long annealing times are required for the transformation between these two structures. Its activation energy is 5.4 eV. We have also studied the various isomers of C 20, since it could form the smallest possible fullerene. At T=0 , the lowest energy isomer is indeed a dodecohedral structure. However, high temperatures favor the corannulene structure, which is a perfect precursor for the formation of C 60. These results are consistent with the experimental data, since high temperatures are needed for efficient formation of C 60. The atomic and electronic structure and doping properties of semiconducting microtubules have also been investigated. The distortions from the ideal geometries are small in microtubules. Substitutional N and B are effective shallow donors and acceptors, respectively. For Al clusters, we focused on Al 13 and Al 55, which can assume perfect icosahedral and cubic structures. However, the distortions from these ideal structures are substantial. For Al 55, several inequivalent but nearly energetically degenerate structures are found. It is shown that this is due to the short range of the screened interatomic interactions.
Ab-Initio Molecular Dynamics Studies of Magnesium-Doped Sodium Clusters
Authors: Röthlisberger Ursula , Andreoni Wanda
Published: November 2004

Structural, electronic, and vibrational properties of NanMg clusters (n=6–9, 18) have been determined using the Car-Parrinello method. We find that in the energetically preferred structures the magnesium impurity is never located at the center of the cluster. The validity of spherical jellium models and the effects of temperature are discussed.
Observation of Highly Charged Sodium Clusters
Authors: Näher U. , Göhlich H. , Lange T. , Martin T.P.
Published: November 2004

Singly charged sodium clusters have been multiply ionized in the drift tube of a TOF-mass-spectrometer. By this method multi-step photoionization of clusters can be examined mass selectively. Up to fourteenfold positively charged clusters have been observed in the mass spectra.

The upper limit for multiple ionization is found to be exclusively a function of cluster size and photon energy. The energy required for each stage of ionization varies with cluster size in a manner well described by a purely classical electrostatic model.
Fullerenes Under Extreme Temperatures and Stress: Collisions of Fullerenes With Surfaces and With Other Fullerenes
Authors: Whetten Robert L. , Yeretzian Chahan
Published: November 2004

The disintegration and coalescence processes of fullerenes have not yet been established, although certain aspects have been known for years. For example, the energy required to fragment C 60 has been calculated to lie in the 11–14 eV range, making it the most stable large molecule known, while reported experimental values are in the 4.5–7 eV range. In this report, we show that surface-impact heating of fullerene-ion beams, when properly calibrated, gives values in agreement with theory. In the last section, new mass spectrometric results on the coalescence reactions of hot fullerene vapors are presented.
GEOMETRICAL AND ELECTRONIC STRUCTURE OF C60 ANIONS
Authors: Stafström Sven
Published: November 2004

The geometrical and electronic structure of various C 60 anions is calculated using a model which couples the bond length to the bond order and to Coulomb interactions between adjacent sites. The total energy of the C 60 anions is minimized with respect to variations in the bond length. The geometrical relaxations of the anions, relative to the neutral molecule, are such that the symmetry of the molecule is lowered (Jahn-Teller distortion). In the case of the mono-anion and the di-anion, the geometrical distortions and the charge are localized to one equatorial line around the spherical molecule. We term this type of self-localized defect a cyclon. The distortions of higher anions are best described as resulting from interacting cyclons. These distortions and the corresponding charges are delocalized over practically the whole system. The Jahn-Teller distortions of the C 60 anions result in a breaking of the degeneracy of the electronic levels and, generally speaking, a broadening of the peaks in the density of states compared to neutral C 60.