The Structural properties of 20Na2O – 10PbO – 10BaO –B2O3 – xPr2O3 glass doped with praseodymium have been investigated. The characterization techniques used for studying rare earth-doped glasses include energy-dispersive X-ray analysis (EDS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) for structural investigations. The concept of physical parameters plays a fundamental role in estimating the strength and structural compactness of the synthesized glass. Consequently, we investigated the influence of rare earth ions (Pr3+) concentration on physical properties. The nature and composition of the synthesized glass samples have been confirmed through Energy Dispersive X-ray Analysis (EDS) and Scanning Electron Microscopy (SEM). The results have been analyzed in view of the modified borate glass network.
In recent work, we discussed the difference between electrons and holes in energy band in solids from a many-particle point of view, originating in the electron-electron interaction[1], and from a single particle point of view, originating in the electron-ion interaction[2]. We proposed that superconductivity in solids only occurs when the Fermi level is close to the top of a band (hole carriers), that it originates in `undressing' of carriers from $both$ the electron-electron and the electron-ion interaction, and that as a consequence holes in the normal state behave like electrons in the superconducting state[3]. However, the connection between both undressing effects was left unclear, as was left unclear how the transformation from hole behavior to electron behavior occurs. Here we clarify these questions by showing that the same electron-electron interaction physics that promotes pairing of hole carriers and undressing of carriers from the electron-electron interaction leads to undressing of carriers from the electron-ion interaction and transforms the behavior of carriers from hole-like to electron-like. Furthermore this phenomenon is connected with the expulsion of negative charge that we predict to occur in superconductors. These unexpected connections support the validity of our theoretical framework, the theory of hole superconductivity, to explain superconductivity in solids.
A recent paper (Phys. Rev A. 75, 022513 (2007), arXiv:cond-mat/0602020) challenges exact time-dependent density functional theory (TDDFT) on several grounds. We explain why these criticisms are either irrelevant or incorrect, and that TDDFT is both formally exact and predictive.
Consequences of different discretizations of the two-dimensional Dirac operator on low energy properties (e.g., the number of nodes) and their relations to gauge properties are discussed. Breaking of the gauge invariance was suggested in a recent work by M. Bocquet, D. Serban, and M.R. Zirnbauer [cond-mat/9910480] in order to destroy an intermediate metallic phase of lattice Dirac fermions with random mass. It is explained that such a procedure is inconsistent with the underlying lattice physics. Previous results point out that the logarithmic growth of the slope of the average density of states with the system size, obtained in the field-theoretical calculation of M. Bocquet et al., could be a precursor for the appearence of an intermediate metallic phase.
Angelini, Pellicoro, and Stramaglia [Phys. Rev. E {\bf 60}, R5021 (1999), cond-mat/9907149] (APS) claim that the phase ordering of two-dimensional systems of sequentially-updated chaotic maps with conserved ``order parameter'' does not belong, for large regions of parameter space, to the expected universality class. We show here that these results are due to a slow crossover and that a careful treatment of the data yields normal dynamical scaling. Moreover, we construct better models, i.e. synchronously-updated coupled map lattices, which are exempt from these crossover effects, and allow for the first precise estimates of persistence exponents in this case.
T. H. Johansen, M. Baziljevich, D. V. Shantsev
et al.
Magneto-opitcal studies of a c-oriented epitaxial MgB2 film with critical current density 10^7 A/cm^2 demonstrate a breakdown of the critical state at temperatures below 10 K [cond-mat/0104113]. Instead of conventional uniform and gradual flux penetration in an applied magnetic field, we observe an abrupt invasion of complex dendritic structures. When the applied field subsequently decreases, similar dendritic structures of the return flux penetrate the film. The static and dynamic properties of the dendrites are discussed.
We analyze high-field current fluctuations in degenerate conductors by mapping the electronic Fermi-liquid correlations at equilibrium to their semiclassical non-equilibrium form. Our resulting Boltzmann description is applicable to diffusive mesoscopic wires. We derive a non-equilibrium connection between thermal fluctuations of the current and resistive dissipation. In the weak-field limit this is the canonical fluctuation- dissipation theorem. Away from equilibrium, the connection enables explicit calculation of the excess ``hot-electron'' contribution to the thermal spectrum. We show that excess thermal noise is strongly inhibited by Pauli exclusion. This behaviour is generic to the semiclassical metallic regime.
Low-temperature dissipation due to vortex motion in strongly anisotropic type-II superconductors with a moderate disorder ($Δ^2/E_F \ll \hbar/τ\ll Δ$) is shown to be determined by the Zener-type transitions between the localized electronic states in the vortex core. Statistics of these levels is described by the random matrix ensemble of the class C defined recently by Atland and Zirnbauer [cond-mat/9602137], so the vortex motion leads naturally to the new example of a parametric statistics of energy levels. The flux-flow conductivity $σ_{xx}$ is a bit lower than the quasiclassical one and {\it grows} slowly with the increase of the electric field.
We discuss the properties of Skyrmions in the Fractional Quantum Hall effect (FQHE). We begin with a brief description of the Chern-Simons-Landau-Ginzburg description of the FQHE, which provides the framework in which to understand a new derivation of the properties of FQHE Skyrmions (S. Baez, A.P. Balachandran, A. Stern and A. Travesset cond-mat/9712151) from anomaly and edge considerations.
Recently we discovered (cond-mat/0212043) that the majority of scientific citations are copied from the lists of references used in other papers. Here we show that a model, in which a scientist picks three random papers, cites them,and also copies a quarter of their references accounts quantitatively for empirically observed citation distribution. Simple mathematical probability, not genius, can explain why some papers are cited a lot more than the other.
We discuss an effect of dc current and dc voltage (stopping bias) generation in a semiconductor superlattice subjected by an ac electric field and its phase-shifted n-th harmonic. In the low field limit, we find a simple dependence of dc voltage on a strength, frequency, and relative phase of mixing harmonics for an arbitrary even value of n. We show that the generated dc voltage has a maximum when a frequency of ac field is of the order of a scattering constant of electrons in a superlattice. This means that for typical semiconductor superlattices at room temperature operating in the THz frequency domain the effect is really observable. We also made a comparison of a recent paper describing an effect of a directed current generation in a semiconductor superlattice subjected by ac field and its second harmonic (n=2) [K.Seeger, Appl.Phys.Lett. 76(2000)82] with our earlier findings describing the same effect [K.Alekseev et al., Europhys. Lett. 47(1999)595; cond-mat/9903092 ]. For the mixing of an ac field and its n-th harmonic with n>=4, we found that additionally to the phase-shift controlling of the dc current, there is a frequency control. This frequency controlling of the dc current direction is absent in the case of n=2. The found effect is that, both the dc current suppression and the dc current reversals exist for some particular values of ac field frequency. For typical semiconductor superlattices such an interesting behavior of the dc current should be observable also in the THz domain. Finally, we briefly review the history of the problem of the dc current generation at mixing of harmonics in semiconductors and semiconductor microstructures.
This paper is a non-technical, informal presentation of our theory of the second law of thermodynamics as a law that is independent of statistical mechanics and that is derivable solely from certain simple assumptions about adiabatic processes for macroscopic systems. It is not necessary to assume a-priori concepts such as "heat", "hot and cold", "temperature". These are derivable from entropy, whose existence we derive from the basic assumptions. See cond-mat/9708200 and math-ph/9805005.
Based on ideas introduced in a previous preprint cond-mat/9701206 we propose an exactly solvable model of bosons interacting amongst themselves via a Van-der Waal-like repulsive interaction, and compute both the filling fraction and the dynamical structure factor exactly. The novelty of this approach involves introducing, analogous to Fermi sea (or surface) displacements, Bose fields that in this case, correspond to fluctuations of the Bose condensate. The exact dynamical structure factor has a coherent part that corresponds to the Bogoliubov spectrum and an incoherent part that is a result of correlations.
We show that the low frequency, long wavelength dynamics of the phase of the pair field for a BCS-type s-wave superconductor at T=0 is equivalent to that of a time-dependent non-linear Schrödinger Lagrangian (TDNLSL), when terms required by Galilean invariance are included. If the modulus of the pair field is also allowed to vary, the system is equivalent to two coupled TDNLSL's. We also refer the interested reader to our earlier paper, `Nonlinear Schrodinger equation for superconductors' [cond-mat/9312099], for a different line of derivation
Joel D. Shore, James P. Sethna, Mark Holzer
et al.
Here, we summarize the most important results of our study of logarithmically slow growth of domains following a quench in two models without randomness in their Hamiltonians. This is a slightly updated version of a paper to appear in the Proceedings of the 1st Annual Tohwa University International Symposium, Fukuoka, Japan (American Institute of Physics, 1992). It is meant to serve as a brief summary of cond-mat/9204015 for those who do not wish to read all the details contained therein (and don't want to hassle with 2 MBytes of tex/ps files).
We investigate the low-energy properties of N-leg integer-spin ladders and tubes with an antiferromagnetic (AF) intrachain coupling. In the odd-leg tubes, the AF rung coupling causes the frustration. To treat all ladders and tubes systematically, we apply Sénéchal's method [Phys. Rev. B 52, 15319 (1995)], based on the nonlinear sigma model. This strategy is valid in the weak interchain (rung) coupling regime. We show that all frustrated tubes possess six-fold degenerate spin-1 magnon bands, as the lowest excitations, while other ladders and tubes have a standard triply degenerate bands. We also consider effects of four kinds of Zeeman terms: uniform, staggered only along the rung, only along the chain, or both directions. The above prediction of the no-field case implies that a sufficiently strong uniform field yields a two-component Tomonaga-Luttinger liquid (TLL) due to the condensation of doubly degenerate lowest magnons in frustrated tubes. In contrast, the field induces a standard one-component TLL in all other systems. This is supported by symmetry and bosonization arguments based on the Ginzburg-Landau theory. The bosonization also suggests that the two-component TLL vanishes and a one-component TLL appears, when the uniform field becomes larger for the second lowest magnon bands to touch the zero-energy line. This transition could be observed as a cusp singularity in the magnetization process. All the analyses for the systems with a staggered Zeeman term suggest that the emergence of the doubly degenerate transverse magnons and the single longitudinal one is universal for the one-dimensional AF spin systems with weak staggered field.