Hasil untuk "cond-mat"

Suset Barroso Solares, Javier Pinto, Gabriele Nanni et al.

Fibrous mats with hydrophobic and oleophilic properties have been fabricated and used as absorbents of oil from stable water in oil emulsions.

A. V. Turlapov, M. Yu. Kagan

Physics of many-body systems where particles are restricted to move in two spatial dimensions is challenging and even controversial: On one hand, neither long-range order nor Bose condensation may appear in infinite uniform 2D systems at finite temperature, on the other hand this does not prohibit superfluidity or superconductivity. Moreover, 2D superconductors, such as cuprates, are among the systems with highest critical temperatures. Ultracold atoms are a platform for studying 2D physics. Uniquely to other physical systems, quantum statistics may be completely changed in an ultracold gas: an atomic Fermi gas may be smoothly crossed over into a gas of Bose molecules (or dimers) by tuning interatomic interactions. We review recent experiments where such crossover has been demonstrated as well as critical phenomena in the Fermi-to-Bose crossover. We also present simple theoretical models describing the gas at different points of the crossover and compare the data to these and more advanced models.

A. Gabrielli, M. Joyce

John A. Wilson

A. Ferraz, E. Kochetov, B. Uchoa

A. Imparato, L. Peliti

We argue that the apparent failure of the work-Hamiltonian connection for free energy calculations reported by Vilar and Rubi' (cond-mat arXiv:0704.0761v2) stems from their incorrect expression for the work.

C. Beenakker, H. Schomerus, P. Silvestrov

The average height of the Coulomb-blockade conductance peaks for chaotic elastic scattering is known to increase by a factor of 4/3 upon breaking time-reversal symmetry. We calculate the temperature dependence of this factor in the regime where the inelastic scattering rate I�in is greater than the mean tunneling rate I�el, which itself is less than the mean level spacing I�. Comparison to recent experimental data by Folk et al. (Folk, Patel, Marcus, DuruA¶z, and Harris, cond-mat/0008052) demonstrates that I�in lies below I�el and hence also below I�, consistent with the low-energy suppression of inelastic electron-electron scattering in quantum dots.

David Chan, D. Eliezer, I. Kogan

We present results of numerical analysis of several simple models for the microstructure of a double auction market without intermediaries which were introduced in cond-mat/9808240. We perform computer simulations of the minimal model in order to verify liquidity scaling laws. A logarithmic correction to the scaling law for midmarket variance is observed, but not for bid-offer spread or its fluctuation, because they are fundamentally different quantities. Time to midmarket sale ($\tau_S$) is found to scale as 1/J while its fluctuation goes as $0.73/J$. A ``reduced'' time ($\tau_{reduced}$) is also studied, and found to scale in a non-trivial way. Asymmetric fluxes are introduced to the minimal model and analytical result derived earlier for the speed of the moving midmarket agrees with numerical results. Simulation of the two-liquid model which describes a market with both market order and limit order traders, reveals widening of the bid-offer spread when the flux of market order traders exceeds that of limit order traders. The variation of the spread with the fraction of market-order traders is investigated. The formula for asymmetric fluxes is applied to the two-liquid model and its predictions are found to agree with experiment. The critical point is approximately determined, and the ratio of the midmarkets for $f = 0.0$ and $f = 0.5$ (where $f$ is the fraction of market-order traders) is calculated.

D. Sornette, Wei‐Xing Zhou

In a recent comment (Johansen A 2003 An alternative view, Quant. Finance 3: C6-C7, cond-mat/0302141), Anders Johansen has criticized our methodology and has questioned several of our results published in [Sornette D and Zhou W-X 2002 The US 2000-2002 market descent: how much longer and deeper? Quant. Finance 2: 468-81, cond-mat/0209065] and in our two consequent preprints [cond-mat/0212010, physics/0301023]. In the present reply, we clarify the issues on (i) the analogy between rupture and crash, (ii) the Landau expansion, ``double cosine'' and Weierstrass-type solutions, (iii) the symmetry between bubbles and anti-bubbles and universality, (iv) the condition of criticality, (v) the meaning of ``bullish anti-bubbles'', (vi) the absolute value of t_c-t, (vii) the fractal log-periodic power law patterns, (viii) the similarity between the Nikkei index in 1990-2000 and the S&P500 in 2000-2002 and (ix) the present status of our prediction.

G. Ódor

Phase transitions of reaction-diffusion systems with a site occupation restriction, particle creation requiring n > 2 parents, and in which explicit diffusion of single particles (A) is possible, are reviewed. Arguments based on mean-field approximation and simulations are given which support novel kind of nonequilibrium criticality. These are in contradiction with the implications of a suggested phenomenological, multiplicative noise Langevin equation approach and with some recent numerical analyses. Simulation results for one- and two-dimensional binary spreading model, 2A ® 4A, 4A ® 2A, reveal a new type of mean-field criticality characterized by the critical exponents a = 1/3 and b = 1/2, as suggested in a recent preprint [cond-mat/0210615]

T. Hyart, K. Alekseev, A-P Leppanen et al.

We theoretically consider the amplication of THz radiation in a superlattice Bloch oscillator. The main dilemma in the realization of THz Bloch oscillator is nding operational conditions which allow simultaneously to achieve gain at THz frequencies and to avoid destructive space-charge instabilities. A possible solution to this dilemma is the extended Limited Space-Charge Accumulation scheme of Kroemer (H. Kroemer, cond-mat/0009311). Within the semiclassical miniband transport approach we extend its range of applicability by considering a dierence in the relaxation times for electron velocity and electron energy. The kinetics of electrons and elds establishing a stationary signal in the oscillator is also discussed.

H. Kee, Yong Baek Kim

The renormalization factor, dubbed "quasiparticle charge" Z e , of the coupling between the supercurrent and quasiparticles was analyzed in the context of high temperature cuprates in a recent paper by Ioffe and Millis [cond-mat/0112509 (unpublished)]. They observed that Z e in cuprates deviates from the BCS value (Z e = 1), which was interpreted as the proximity effect near a Mott insulator. Here we show that the deviation from Z e = I can occur, in general, even in the absence of quasiparticle interactions, when the superconducting order coexists with another order parameter with the same internal symmetry. As an example, we compute the coefficient of the linear temperature dependence of the superfluid density when the d-wave superconducting state coexists with the orbital antiferromagnetic state (d-density wave), and find that Z e varies from 1/√2 to 1.

E. Marinari, G. Parisi

We show that the evidence of cond-mat/9906323 does not discriminate among droplet model and mean field like behavior.

Y. S. Jain

Energy of elementary excitations and the anomalous nature of small Q phonons in He-II are studied by using our macro-orbital microscopic theory of a system of interacting bosons (cond-mat/0606571). It is observed that : (i) the experimental E(Q) of He-II not only agrees with our theoretical relation $E(Q) = \hbar^2Q^2/4mS(Q)$ but also supports an important conclusion of Price that S(0) should have zero value for quantum fluids, and (ii) Feynman's energy of excitations $E(Q)_{Fyn} = \hbar^2Q^2/2mS(Q)$ equals approximately to $2E(Q)_{exp}$ even at low Q. Three problems with the Feynman's inference that $E(Q)_{Fyn}$ has good agreement with $E(Q)_{exp}$ at low Q are identified. It is argued that the theory can also be used to understand similar spectrum of the BEC state of a dilute gas reported by O'Dell et al.

H. Luo, T. Xiang, X. Q. Wang et al.

In a recent Comment, Kolf et al. (cond-mat/0503669) state that our analysis of the Fano resonance for Anderson impurity systems [Luo et al., Phys. Rev. Lett 92, 256602 (2004)] is incorrect. Here we want to point out that their comments are not based on firm physical results and their criticisms are unjustified and invalid.

Yue Yu

We derive a microscopic model describing low-lying edge excitations in a fractional quantum Hall liquid with v = v*/(phi v* + 1). For v* > 0, it is found that the composite-fermion model reduces to an SU(v*) Calogero-Sutherland model in a dimension reduction, whereas it is not exactly soluble for v* < 0. However, the ground states in both cases can be found, and the low-lying excitations can show chiral Luttinger-liquid behaviors. On the other hand, we show that the finite-temperature behavior of the G-T curve will deviate from the prediction of the chiral Luttinger liquid. We also point out that the suppression of the "spin'' degrees of freedom agrees with very recent experiments by Chang et al. [Phys. Rev. Lett. 77, 2538 (1996)]. The two-boson model of Lee and Wen (preprint, cond-mat/9801318) is described microscopically.

D. Sornette, K. Leung, J. Andersen

We argue that the existence of abrupt failure in the democratic fiber bundle model is more general than concluded by da Silveira in his comment (cond-mat/9709327). We refute his claim that the nature of the rupture process in the DFBM depends on the ``disorder distribution only via its large failure strength behavior''.

Lei Yang, P. Grassberger

Recently, it has been claimed (O. V. Gendelman and A. V. Savin, Phys. Rev. Lett. {\bf 84}, 2381 (2000); A.V.Savin and O.V.Gendelman, arXiv: cond-mat/0204631 (2002)) that two nonlinear classical 1-d lattice models show transitions, at finite temperatures, where the heat conduction changes from being finite to being infinite. These are the well known Frenkel-Kontorova (FK) model and a model for coupled rotators. For the FK model we give strong theoretical arguments why such a phase transition is not to be expected. For both models we show numerically that the effects observed by Gendelman {\it et al.} are not true phase transitions but are rather the expected cross-overs associated to the conductivity divergence as $T\to 0$ and (for the FK model) $T\to\infty$.

J.A.G. Orza, Ricardo Brito, M. H. Ernst

Replacement of cond-mat/0002383. Re-analysis of computer simulations, new figures and modification of conclusions.

T. Kennedy

We consider the highly anisotropic ferromagnetic spin 1/2 Heisenberg chain with periodic boundary conditions. In each sector of constant total z component of the spin, we develop convergent expansions for the lowest band of eigenvalues and eigenfunctions. These eigenstates describe droplet states in which the spins essentially form a single linear droplet which can move. Our results also give a convergent expansion for the dispersion relation, i.e., the energy of the droplet as a function of its momentum. The methods used are from math-ph/0208026 and cond-mat/0104199, and this short paper should serve as a pedagogic introduction to those papers.