Showing papers in "International Journal of Modern Physics B in 1998"
TL;DR: In this paper, Monte Carlo simulations of the short-time critical dynamics are reviewed and the universal scaling behavior of the dynamic Ising model and Potts model are discussed in detail, while extension and application to more complex systems as the XY model, the fully frustrated XY model and other dynamic systems are also presented.
Abstract: Monte Carlo simulations of the short-time critical dynamics are reviewed. The short-time universal scaling behavior of the dynamic Ising model and Potts model are discussed in detail, while extension and application to more complex systems as the XY model, the fully frustrated XY model and other dynamic systems are also presented. The investigation of the universal behavior of the short-time dynamics not only enlarges the fundamental knowledge on critical phenomena but also, more interestingly, provides possible new ways to determine not only the new critical exponents θ and θ1, but also the traditional dynamic critical exponent z as well as all static critical exponents.
185 citations
TL;DR: In this article, a sintered TiO2 was synthesized by an ion beam sputtering cold condensation (IBS-CC) technique, which was used to synthesize nanoparticles.
Abstract: Nanoparticles of TiO2 have been synthesized by an ion beam sputtering-cold condensation (IBS-CC) technique. A sintered TiO2 was sputtered by an ion beam (Kaufman source, 900 eV, Ar+ ions) and the e...
155 citations
TL;DR: In this paper, the importance of a morphological characterization of patterns in statistical physics was pointed out, and integral geometry furnishes a suitable family of morphological descriptors, known as Minkowski functionals, which characterize not only the connectivity but also the content and shape of spatial patterns.
Abstract: The aim of this paper is to point out the importance of a morphological characterization of patterns in Statistical Physics. Integral geometry furnishes a suitable family of morphological descriptors, known as Minkowski functionals. They characterize not only the connectivity (topology) but also the content and shape (geometry) of spatial patterns. Integral geometry provides also powerful theorems and formulae, which makes the calculus convenient for many models of stochastic geometries, for instance, for the Boolean grain model. This model generates random structures in space by overlapping bodies or "grains" (balls, sticks) each with arbitrary location and orientation. We illustrate the integral geometric approach to stochastic geometries by applying morphological measures to such diverse topics as percolation, complex fluids, and the large-scale structure of the universe: (A) Porous media may be generated by overlapping holes of arbitrary shape distributed uniformly in space. The percolation thresold of such porous media can be estimated accurately in terms of the morphology of the distributed pores. (B) Under rather natural assumptions a general expression for the Hamiltonian of complex fluids can be derived that includes energy contributions related to the morphology of the spatial domains of homogeneous mesophases. We find that the Euler characteristic in the Hamiltonian stabilizes a highly connected bicontinuous structure resembling the middle-phase in oil-water microemulsions, for instance. (C) Morphological measures are a novel method for the description of complex spatial structures aiming for relevant order parameters and structure information complement to correlation functions. Typical applications address Turing patterns in chemical reaction diffusion systems, homogeneous phases evolving during spinodal decomposition, and the distribution of galaxies and clusters of galaxies in the Universe as a prominent example of a point process in nature.
137 citations
TL;DR: In this paper, the nodal liquid, a novel zero-temperature quantum phase obtained by quantum disordering a d-wave superconductor, was introduced and studied, which has numerous remarkable properties which lead to suggest it as an explanation of the pseudo-gap state in under-doped high temperature superconductors.
Abstract: We introduce and study the nodal liquid, a novel zero-temperature quantum phase obtained by quantum-disordering a d-wave superconductor. It has numerous remarkable properties which lead us to suggest it as an explanation of the pseudo-gap state in underdoped high-temperature superconductors. In the absence of impurities, these include power-law magnetic order, a T-linear spin susceptibility, nontrivial thermal conductivity, and two- and one-particle charge gaps, the latter evidenced, e.g. in transport and electron photoemission (which exhibits pronounced fourfold anisotropy inherited from the d-wave quasiparticles). We use a (2+1)-dimensional duality transformation to derive an effective field theory for this phase. The theory is comprised of gapless neutral Dirac particles living at the former d-wave nodes, weakly coupled to the fluctuating gauge field of a dual Ginzburg–Landau theory. The nodal liquid interpolates naturally between the d-wave superconductor and the insulating antiferromagnet, and our effective field theory is powerful enough to permit a detailed analysis of a panoply of interesting phenomena, including charge ordering, antiferromagnetism, and d-wave superconductivity. We also discuss the zero-temperature quantum phase transitions which separate the nodal liquid from various ordered phases.
112 citations
TL;DR: In this article, two-leg S = 1/2 ladders with general isotropic exchange interactions between spins on neighboring rungs, whose ground states can be found exactly in a form of finitely correlated wave function are found: one yields translationally invariant ground states and the other describes spontaneously dimerized models with twofold degenerate ground states.
Abstract: We study two-leg S=1/2 ladders with general isotropic exchange interactions between spins on neighboring rungs, whose ground state can be found exactly in a form of finitely correlated (matrix product) wave function. Two families of models admitting an exact solution are found: one yields translationally invariant ground states and the other describes spontaneously dimerized models with twofold degenerate ground state. Several known models with exact ground states (Majumdar–Ghosh and Shastry–Sutherland spin-1/2 chains, Affleck–Kennedy–Lieb–Tasaki spin-1 chain, Δ-chain, Bose–Gayen ladder model) can be obtained as particular cases from the general solution of the first family, which includes also a set of models with only bilinear interactions. Those two families of models have nonzero intersection, which enables us to determine exactly the phase boundary of the second-order transition into the dimerized phase and to study the properties of this transition. The structure of elementary excitations in the dimerized phase is discussed on the basis of a variational ansatz. For a particular class of models, we present exact wave functions of the elementary excitations becoming gapless at second-order transition lines. We also propose a generalization of the Bose–Gayen model which has a rich phase diagram with all phase boundaries being exact.
84 citations
TL;DR: In this article, the authors describe a simple method for obtaining a random number generator based on the property of the logistic map, which is able to generate an infinite chaotic sequence of numbers.
Abstract: For the largest value of the control parameter, the logistic map is able to generate an infinite chaotic sequence of numbers. Here we describe a simple method for obtaining a random number generator based on this property of the logistic map. Comparing to usual congruential random generators, which are periodic, the logistic random number generator is infinite, aperiodic and not correlated. An aperiodic random number generator is a valuable tool for computer simulation methods.
79 citations
TL;DR: In this article, a simple computational model is proposed that reproduces various aspects of the complex dynamics of dunes such as the barchan dunes formation process, the evolution process from a barcharan dune to a seif dune, the network-dunes formation under time-dependent directional winds, etc.
Abstract: A simple computational model is proposed that reproduces various aspects of the complex dynamics of dunes such as the barchan dunes formation process, the evolution process from a barchan dune to a seif dune, the network-dunes formation under time-dependent directional winds, etc. Although this model may be oversimplified in several respects, there is a hope that it helps us to sift relevant factors out the vast sea of numerous factors influencing the rich dynamics of desert dunes.
78 citations
TL;DR: In this article, the first principles tight-binding linear muffin-tin orbital method within the local density approximation (LDA) has been used to calculate the ground state properties structural phase transition and pressure dependence of the band gap of BeS, BeSe and BeTe.
Abstract: The first principles tight-binding linear muffin-tin orbital method within the local density approximation (LDA) has been used to calculate the ground state properties structural phase transition and pressure dependence of the band gap of BeS, BeSe and BeTe. We have calculated the energy-volume relations for these compounds in the B3 and B8 phases. The calculated lattice parameters, bulk modulus and the pressure-volume relation were found to be in good agreement with the recent experimental results. We have also calculated the cohesive energy for them and they are consistent with the bulk modulus. The calculated B3 to B8 structural transition pressure for BeS, BeS and BeTe agree well with the experimental results. Our calculations show that these compounds are indirect band gap (Γ-X) semiconductors at ambient conditions. The calculated band gap values are found to be underestimated by 20–30% which is due to the usage of LDA. After the structural transition to the B8 phase BeS continues to be indirect band gap semiconductor and ultimately it becomes metallic above 100 GPa. BeSe and BeTe are metallic at B3 to B8 structural transition.
51 citations
TL;DR: In this article, the authors discuss possible quantum mechanical aspects of MicroTubules (MT) based on recent developments in quantum physics and present a novel scenario on the formation of macroscopic (or mesoscopic) quantum-coherent states, as a result of the (quantum-electromagnetic) interactions of the MT dimers with the surrounding molecules of the ordered water in the interior of the microtubules.
Abstract: We discuss possible quantum mechanical aspects of MicroTubules (MT), based on recent developments in quantum physics. We focus on potential mechanisms for "energy-loss-free" transport along the microtubules, which could be considered as realizations of Frohlich's ideas on the role of solitons for superconductivity and/or biological matter. In particular, by representing the MT arrangements as cavities, we present a novel scenario on the formation of macroscopic (or mesoscopic) quantum-coherent states, as a result of the (quantum-electromagnetic) interactions of the MT dimers with the surrounding molecules of the ordered water in the interior of the MT cylinders. Such states decohere due to dissipation through the walls of the MT. Transfer of energy without dissipation, due to such coherent modes, could occur only if the decoherence time is larger than the average time scale required for energy transfer across the cells. We present some generic order of magnitude estimates or the decoherence time in a typical model for MT dynamics. Our conclusion is that the quantum coherent states play a role in energy transfer if the dissipation through the walls of the MT cavities is fairly suppressed, corresponding to damping time scales Tr≥10-4-10-5 sec, for moderately large MT networks. We suggest specific experiments to test the above-conjectured quantum nature of the microtubular arrangements inside the cell. These experiments are similar in nature to those in atomic physics, used in the detection of the Rabi-Vacuum coupling between coherent cavity modes and atoms. Our conjecture is that a similar Rabi-Vacuum-splitting phenomenon occurs in the absorption (or emission) spectra of the MT dimers, which would constitute a manifestation of the dimer coupling with the coherent modes in the ordered-water environment (dipole quanta), which emerge due to "super-radiance".
47 citations
TL;DR: The two-dimensional Hubbard model is analyzed in the framework of the two-pole expansion in this article, and it is demonstrated that several theoretical approaches, when considered at their lowest level, are all equivalent and share the property of satisfying the conservation of the first four spectral momenta.
Abstract: The two-dimensional Hubbard model is analyzed in the framework of the two-pole expansion It is demonstrated that several theoretical approaches, when considered at their lowest level, are all equivalent and share the property of satisfying the conservation of the first four spectral momenta It emerges that the various methods differ only in the way of fixing the internal parameters and that it exists a unique way to preserve simultaneously the Pauli principle and the particle–hole symmetry A comprehensive comparison with respect to some general symmetry properties and the data from quantum Monte Carlo analysis shows the relevance of imposing the Pauli principle
39 citations
TL;DR: In this paper, the reset model and its (in part analytically soluble) mean field version have been briefly introduced in Letters, where the average fitness in the system increases logarithmically with time, while the rate of extinction steadily decreases.
Abstract: After an introductory section summarizing the paleontological data and some of their theoretical descriptions, we describe the "reset" model and its (in part analytically soluble) mean field version, which have been briefly introduced in Letters.1,2 Macroevolution is considered as a problem of stochastic dynamics in a system with many competing agents. Evolutionary events (speciations and extinctions) are triggered by fitness records found by random exploration of the agents' fitness landscapes. As a consequence, the average fitness in the system increases logarithmically with time, while the rate of extinction steadily decreases. This non-stationary dynamics is studied by numerical simulations and, in a simpler mean field version, analytically. We also consider the effect of externally added "mass" extinctions. The predictions for various quantities of paleontological interest (life-time distribution, distribution of event sizes and behavior of the rate of extinction) are robust and in good agreement with available data.
TL;DR: In this paper, the general spin-S Blume-Capel model is studied within two different approaches: the pair approximation for the free energy, and Monte Carlo simulations for S = 1, 3/2, and 2 on simple cubic lattices.
Abstract: The general spin-S Blume–Capel model is studied within two different approaches: the pair approximation for the free energy, and Monte Carlo simulations. The global phase diagram in the temperature-anisotropy plane is obtained for general values of S in the pair approximation and the results are qualitatively the same as those of the usual mean field theory. Special interest is given in the low temperature region of the phase diagram where a number of first-order lines emerge from a multiphase point at the ground state. Monte Carlo simulations for S=1, 3/2, and 2 on simple cubic lattices also confirm the general trend of the mean field like approach, and in the special S=3/2 case the present results are in disagreement with previous Monte Carlo simulations, as well as renormalization group calculations on corresponding two-dimensional lattices.
TL;DR: In this paper, the first principles tight-binding linear muffin-tin orbital method within the local density approximation was used to calculate the electronic band structures and the total energies of CaS, CaSe and CaTe in NaCl-type and CsCl -type structures.
Abstract: The first principles tight-binding linear muffin-tin orbital method within the local density approximation was used to calculate the electronic band structures and the total energies of CaS, CaSe and CaTe in NaCl-type and CsCl-type structures. The total energies were used to calculate the ground state properties such as lattice parameter, bulk modulus and the structural phase stability of these compounds. The transition pressure at which these compounds undergo the structural phase transition from NaCl-type to CsCl-type structure were calculated. The ground state properties, the transition pressures and the transition volumes are found to agree with the experimental and other theoretical results. The energy band gap at ambient condition in the NaCl-type structure were calculated and compared with the experimental results available for CaS and CaSe. For CaTe the experimental values of energy gap are not available. The valence-band width and the pressure coefficient of energy gap were also calculated. The closure of band gap at transition in CsCl structure for CaSe, and CaTe were explained by comparing the band structures of BaSe and SrSe in this phase.
TL;DR: Theory of spin-reflection positivity developed in recent years is reviewed in this article, which makes use of symmetries in an electron system and theory of matrix to investigate the ground state properties.
Abstract: Theory of spin-reflection positivity developed in recent years is reviewed. This theory makes use of symmetries in an electron system and theory of matrix to investigate the ground state properties. Existences of anti- and ferromagnetic long-range orders in itinerant electron systems, and of off-diagonal long-range order are two successful applications of the theory. In this article, the author attempt to summarize exact results proved by utilizing this theory and related topics. First a general theory and basic theorems are introduced. Second, based on the band structures of conduction electrons, existences of a singlet state with strongly antiferromagnetic correlation, a state with both anti- and ferromagnetic long-range orders, and a fully saturated ferromagnetic state are proved. The theory is applied to several of the main theoretical models for strongly correlated electron systems, such as the Heisenberg model, the Hubbard model, the Anderson model, the single- and multichannel Kondo model, and the generalized Hubbard model, and a series of rigorous results are found in these models. Third, it is proved that off-diagonal long-range order and charge-density wave exist in the ground states of the attractive Hubbard model and the generalized Hubbard model. A relation between pseudospin symmetry and the uniform density theorem is introduced. Fourth, the theory is applied successfully to explain experimental observations of oscillatory interlayer magnetic coupling in ultrathin magnetic films. Finally several unsolved problems are discussed. All results introduced in this article are mathematically exact.
TL;DR: In this article, a lattice model with pairwise additive interactions is proposed, where parameters defining the pair potential are expressed as linear combinations of elastic constants. But the potential energy is not pair-wise additive unless the three elastic constants are set to a common value, thus reducing the potential to the well-known Lebwohl-Lasher model.
Abstract: Director configurations in nematic Liquid Crystals can be determined by minimizing their elastic free-energy density, on the basis of elastic constants and of specific boundary conditions; in some published cases, this has been obtained by numerical procedures where the elastic free-energy density plays the same role as the overall potential energy in a standard Monte Carlo simulation. The "potentials" used in these papers are short-ranged but, in general, not pairwise additive, unless the three elastic constants are set to a common value, thus reducing the potential to the well-known Lebwohl–Lasher lattice model. On the other hand, one can construct, possibly in different ways, a lattice model with pairwise additive interactions, approximately reproducing the elastic free-energy density, where parameters defining the pair potential are expressed as linear combinations of elastic constants; a nematogenic pair interaction of this kind, originally proposed by Gruhn and Hess (T. Gruhn and S. Hess, Z. Naturforsch.A51, 1 (1996)), has been investigated here by Monte Carlo simulation with periodic boundary conditions, i.e. aimed at the resulting bulk behavior.
TL;DR: In this article, the convergence of the derivative expansion was studied and the role of reparametrization invariance in the convergence is discussed. But the convergence was not considered.
Abstract: Approximation only by derivative (or more generally momentum) expansions, combined with reparametrization invariance, turns the continuous renormalization group into a set of partial differential equations which at fixed points become nonlinear eigenvalue equations for the anomalous scaling dimension η. We review how these equations provide a powerful and robust means of discovering and approximating non-perturbative continuum limits. Gauge fields are briefly discussed. Particular emphasis is placed on the role of reparametrization invariance, and the convergence of the derivative expansion is addressed.
TL;DR: In this article, the authors investigated the properties of two polymorphic liquid crystals, namely, 4-nonyloxy-4-butoxyphenyl benzoate and N-(4-heptyloxybenzylidene-4butylaniline) in a wide temperature range, particularly, in the phase transition regions.
Abstract: This work presents our investigations of mezomorphic properties of two polymorphic liquid crystals, namely, 4-nonyloxy-4-butoxyphenyl benzoate and N-(-4-heptyloxybenzylidene-4-butylaniline) in a wide temperature range, particularly, in the phase transition regions. By means of an original experimental method, the heterophase regions and also the phase transition temperatures have been determined for these materials with high accuracy. These phase transition intervals have been analyzed using a mean field model.
TL;DR: In this article, the dynamics of a pair of spins coupled to each other and also to an environmental sea of oscillators are solved for three regimes, viz., (i) the "locked" regime, where the two spins lock together; (ii) the 'correlated relaxation' regime (mutually correlated incoherent relaxation); and'mutual coherence' regime, with correlated damped oscillations.
Abstract: We solve for the dynamics of a pair of spins, coupled to each other and also to an environmental sea of oscillators. The environment mediates an indirect interaction between the spins, causing both mutual coherence effects and dissipation. This model describes a wide variety of physical systems, ranging from 2 coupled microscopic systems (e.g. magnetic impurities, chromophores, etc.), to 2 coupled macroscopic quantum systems. We obtain analytic results for 3 regimes, viz., (i) The "locked" regime, where the 2 spins lock together; (ii) The "correlated relaxation" regime (mutually correlated incoherent relaxation); and (iii) The "mutual coherence" regime, with correlated damped oscillations. These results cover most of the parameter space of the system.
TL;DR: In this article, it was shown that the photoemission experiments of the purported superconducting gap in Bi2Sr2CaCu2O8+δ are entirely consistent with charge-and/or spin-density wave formation in that material.
Abstract: In recent years, there has been a raging controversy regarding the orbital symmetry of the superconducting order parameter (OP) in the high temperature superconductors. Many experiments were interpreted in terms of a dx2-y2-wave OP, but many others were interpreted in terms of a more conventional s-wave OP. We review the problems of both intrinsic and extrinsic natures with the phase-sensitive experiments on YBCO. We further show that the photoemission experiments of the purported superconducting gap in Bi2Sr2CaCu2O8+δ are entirely consistent with charge- and/or spin-density wave formation in that material. The presence of such density waves greatly complicates the analysis of most experiments. Hence, we conclude that the orbital symmetry of the superconducting OP is still unknown in any of the high temperature superconductors.
TL;DR: In this article, a short discussion of theoretical calculations of the optical properties of quasi-one and quasi-bidimensional molecular crystals is presented, with special attention devoted to the electron-molecular vibration coupling which is analyzed in charge-transfer salts with tetrathiafulvalene derivatives (including giant analoges of TTF) as donor components.
Abstract: A short discussion of theoretical calculations of the optical properties of quasi-one and quasi-bidimensional molecular crystals is presented. Special attention is devoted to the electron–molecular vibration coupling which is analyzed in charge-transfer salts with tetrathiafulvalene (TTF) derivatives (including giant analoges of TTF) as donor components.
TL;DR: In this paper, the authors consider the one-dimensional delta-interacting electron gas in the case of infinite repulsion and derive differential equations which drive the correlation functions, which describe power law behavior and exponential decay as functions of temperature, magnetic field and chemical potential.
Abstract: We consider the one-dimensional delta-interacting electron gas in the case of infinite repulsion. We use determinant representations to study the long time, large distance asymptotics of correlation functions of local fields in the gas phase. We derive differential equations which drive the correlation functions. Using a related Riemann–Hilbert problem we obtain formulae for the asymptotics of the correlation functions, which are valid at all finite temperatures. At low temperatures these formulae lead to explicit asymptotic expressions for the correlation functions, which describe power law behavior and exponential decay as functions of temperature, magnetic field and chemical potential.
TL;DR: In this paper, the Saffman-Taylor viscous fingering problem in rectangular geometry is analyzed and the onset of nonlinear effects and the basic symmetries of the mode coupling equations are investigated.
Abstract: We analyze the Saffman–Taylor viscous fingering problem in rectangular geometry We investigate the onset of nonlinear effects and the basic symmetries of the mode coupling equations, highlighting the link between interface asymmetry and viscosity contrast Symmetry breaking occurs through enhanced growth of sub-harmonic perturbations Our results explain the absence of finger tip-splitting in the early flow stages, and saturation of growth rates compared with the predictions of linear stability
TL;DR: In this paper, the authors measured the micro-Raman scattering by highly oriented crystalline aluminum nitride films and analyzed the defect scattering using the phonon confinement model, which revealed that the films are highly oriented with the wurtzite c-axis direction normal to the film plane.
Abstract: Micro-Raman scattering by highly oriented crystalline aluminum nitride has been measured. Phonon modes in AlN were identified in different scattering geometry configurations and scattering polarizations. The phonon modes revealed that aluminum nitride films are highly oriented with the wurtzite c-axis direction normal to the film plane. The Raman scattering modes are broadened and shifted due to grain boundaries and other defects in the films. The defect scattering was analysed using the phonon confinement model. These results were compared with results obtained from X-ray diffraction powder patterns and high-resolution transmission electron microscopy.
TL;DR: The lattice parameters from powder diffraction measurements were calculated and shown to be very close to those previously reported Crystallite size measurements indicated that the films were nanocrystalline, the size decreasing as a function of dopant concentration as mentioned in this paper.
Abstract: Thin films of Ce1-xYxO2-y where x ranges from 0 to 05 have been coated onto glass substrates using an inorganic sol–gel approach at low temperature The lattice parameters from powder diffraction measurements were calculated and shown to be very close to those previously reported Crystallite size measurements indicated that the films were nanocrystalline, the size decreasing as a function of dopant concentration The films are transparent in the region 500 to 1500 nm with very low optical losses The film refractive index is dependent on the dopant concentration and peaks at an yttria concentration of x=025 after treatment at 450°C, with a value of 179, which on increasing the yttria concentration to x=050 decreases to 165 in the dispersion free region The optical band gap is also dependent on the dopant concentration and is in the range 32 to 30 eV
TL;DR: In this article, a T-5 behavior of the out-of-plane superfluid density rho(s)(c) for clean tetragonal HTSC was predicted and observed experimentally in the single layer Hgcompound HgBa2CuO4+delta.
Abstract: We have reviewed our theoretical and experimental results of the low temperature superfluid response function rho(s)(mu) of high temperature superconductors (HTSC). In clean high-T-c materials the in-plane superfluid density rho(s)(ab) varies linearly with temperature. The slope of this linear T term is found to scale approximately with 1/T-c which, according to the weak coupling BCS theory for a d-wave superconductor, implies that the gap amplitude scales approximately with T-c. A T-5 behavior of the out-of-plane superfluid density rho(s)(c) for clean tetragonal HTSC was predicted and observed experimentally in the single layer Hg-compound HgBa2CuO4+delta. In other tetragonal high-T-c compounds with relatively high anisotropy, such as Hg2Ba2Ca2Cu3O8-delta, rho(s)(c) varies as T-2 due to disorder effects. In optimally doped YBa2Cu3O7-delta, rho(s)(c) varies linearly with temperature at low temperatures, but in underdoped YBa2Cu3O7-delta, rho(s)(c) varies as T-2 at low temperatures; these results are consistent with our theoretical calculations.
TL;DR: In this paper, the effects of constant external magnetic fields on excitations about the superconducting state in planar systems were examined, and it was shown that for an even number of Dirac fermion species, required in our model as a result of gauging a particle-hole SU(2) symmetry, Parity or Time Reversal violation does not necessarily occur.
Abstract: Within the framework of a relativistic non-Abelian gauge theory approach to the physics of spin–charge separation in doped quantum antiferromagnetic planar systems, proposed recently by the authors, we are examining here the effects of constant external magnetic fields on excitations about the superconducting state in the model. The electrically-charged Dirac fermions (holons), describing excitations about specific points on the fermi surface, e.g. those corresponding to the nodes of a d-wave superconducting gap in high-Tc cuprates, condense, resulting in the opening of a Kosterlitz–Thouless–like gap (KT) at such nodes. This leads, in general, to a second superconducting phase transition, which occurs at low temperatures, in addition to the high-Tc superconductivity due to the bulk of the fermi surface for holons in a (d-wave) spin–charge separated superconductor. In the presence of strong external magnetic fields at the surface regions of the planar superconductor, in the direction perpendicular to the superconducting planes, these KT gaps appear to be enhanced. Our preliminary analysis, based on analytic Schwinger–Dyson treatments, seems to indicate that for an even number of Dirac fermion species, required in our model as a result of gauging a particle–hole SU(2) symmetry, Parity or Time Reversal violation does not necessarily occurs. Based on these considerations, we argue that recent experimental findings, concerning thermal conductivity plateaux of quasiparticles in planar high-Tc cuprates in strong external magnetic fields, may indicate the presence of such KT gaps, caused by charged Dirac-fermion excitations in these materials, as suggested in the above model.
TL;DR: In this article, the ground state structures, vibrational spectra cohesive energies and HOMO-LUMO gaps of small SinHm clusters (n=1, 2 and m=1-6) and their deuterated derivatives based on the nonorthogonal tight-binding molecular dynamics scheme were obtained by using simulated annealing.
Abstract: We report a systematic study of ground state structures, vibrational spectra cohesive energies and HOMO-LUMO gaps of small SinHm clusters (n=1, 2 and m=1–6) and their deuterated derivatives based on the nonorthogonal tight-binding molecular dynamics scheme. The ground state structures have been obtained by using simulated annealing. The bond lengths, bond angles and the frequencies of normal modes are found to be in good agreement with available experimental data and ab initio calculations. Our calculation of cohesive energies indicate SiH2 to be more stable than SiH3 or SiH and Si2H4, more stable than Si2H3 or Si2H5.
TL;DR: In this article, a systematic study of ground state structures, vibrational spectra, cohesive energies and HOMO-LUMO gaps of small SinH clusters (n=3, 10) based on the nonorthogonal tight-binding molecular dynamics scheme was performed.
Abstract: We report a systematic study of ground state structures, vibrational spectra, cohesive energies and HOMO-LUMO gaps of small SinH clusters (n=3, 10) based on the nonorthogonal tight-binding molecular dynamics scheme. The ground state structures have been obtained by using simulated annealing. In particular, we focus on how the addition of a hydrogen atom affects the ground state geometry and the stability of a Sin cluster. We find that hydrogen either enters into the surface of the cluster or occupies a position outside the cluster. In the first case, it drastically distorts the cluster, while in the latter, there is very little distortion. We find that in some cases SinH cluster has some resemblance with Sin+1 cluster. We also find that hydrogen can form bonds with more than one silicon atom. Our calculation indicates that SiH, Si3H and Si5H will be more stable and Si4H, Si6H, Si7H, Si9H and Si10H will be less stable clusters.
TL;DR: In this paper, the effect of the Berry phase associated with the JT distortions on the band motion of an eg electron was investigated, and the formation of paired Jahn-Teller stripes and the stabilization mechanism of the CE-type antiferromagnetism in agreement with experiment.
Abstract: In order to gain an insight into the formation of paired Jahn–Teller (JT) stripes, we have investigated the electronic and vibronic structures in the manganese oxides by paying due attention to the effect of the Berry phase associated with the JT distortions on the band motion of an eg electron. In terms of a band-insulator picture, we have succeeded in obtaining the JT stripes and the stabilization mechanism of the CE-type antiferromagnetism in agreement with experiment.
TL;DR: In this article, the authors present a two-stage exposition on phase separation in binary mixtures with simple chemical reactions, which involve only the components A and B of the mixture.
Abstract: This paper is the second in a two-stage exposition on phase separation in binary (AB) mixtures with simple chemical reactions, which involve only the components A and B of the mixture. In this paper, we present details of our modelling, which employs the master equation formalism, for a number of different reactions. We also present detailed numerical results which supplement those in our previous paper (S. Puri and H. L. Frisch, J. Phys.A27, 6027 (1994)).