Hasil untuk "cond-mat"

I. Krasnova, A. Olšteine

Evelyn Tang, L. Fu

G. Wright, A. Pustina, R. Mikat et al.

M. V. Ramallo, C. Carballeira, R. I. Rey et al.

Some of the in-plane paraconductivity measurements that Rullier-Albenque and coworkers have presented in a recent manuscript (cond-mat/1102.2804) are compared here with the Gaussian-Ginzburg-Landau (GGL) approach for layered superconductors, extended by Carballeira and coworkers [Phys. Rev. B 63, 144515 (2001)] to high reduced-temperatures by introducing a so-called total-energy cuto. In contrast with the conclusions of Rullier-Albenque and coworkers, it is shown that these experimental data may be explained at a quantitative level, in all the reduced-temperature regions covered by the measurements, by this extended GGL approach.

P. Oikonomou, I. Rushkin, I. Gruzberg et al.

Standard Schramm–Loewner evolution (SLE) is driven by a continuous Brownian motion which then produces a trace, a continuous fractal curve connecting the singular points of the motion. If jumps are added to the driving function, the trace branches. In a recent publication (Rushkin et al 2006 J. Stat. Mech. P01001 [cond-mat/0509187]) we introduced a generalized SLE driven by a superposition of a Brownian motion and a fractal set of jumps (technically a stable Lévy process). We then discussed the small scale properties of the resulting Lévy-SLE growth process. Here we discuss the same model, but focus on the global scaling behavior which ensues as time goes to infinity. This limiting behavior is independent of the Brownian forcing and depends upon only a single parameter, α, which defines the shape of the stable Lévy distribution. We learn about this behavior by studying a Fokker–Planck equation which gives the probability distribution for end points of the trace as a function of time. As in the short time case previously studied, we observe that the properties of this growth process change qualitatively and singularly at α = 1. We show both analytically and numerically that the growth continues indefinitely in the vertical direction for α>1, goes as logt for α = 1, and saturates for α<1. The probability density has two different scales corresponding to directions along and perpendicular to the boundary. In the former case, the characteristic scale is X(t)∼t1/α. In the latter case the scale is Y (t)∼A+Bt1−1/α for , and Y (t)∼lnt for α = 1. Scaling functions for the probability density are given for various limiting cases.

W. Mentzer, Ella Collier

K. Kanki, Hiroshi Kontani

This is a reply to the comment by O. Narikiyo (cond-mat/0012505) on our paper J. Phys. Soc. Jpn. {\bf 68}, (1999) 1614. We point out mistakes about his arguments, and we show that our analysis is compatible with the established Fermi liquid theory, so the obtained result is justified.

Z. Xiao, O. Dogru, E. Andrei et al.

P. Sindzingre, J. Fouet, C. Lhuillier

Exact diagonalizations indicate that the effective 1-dimensional behavior (sliding Luttinger liquid phase) of the frustrated spin-1/2 crossed chain model, predicted by Starykh, Singh and Levine [Phys. Rev. Lett. 88, 167203 (2002)], persists for a wide range of transverse couplings. The extension of the other phases (plaquette valence bond crystal and Neel long range order) is precised. No clear indication of a coexistence of these two phases is found, at variance with a suggestion of Sachdev and Park (cond-mat/0108214).

M. Takigawa, O. Starykh, A. Sandvik et al.

The NMR relaxation data on Sr_2CuO_3 [Phys. Rev. Lett. 76, 4612 (1996)] are reexamined and compared with the analytic theory of the dynamic susceptibility in the S=1/2 antiferromagnetic Heisenberg chain including multiplicative logarithmic corrections [Phys. Rev. Lett. 78, 539 (1997); cond-mat/9610015]. Comparisons of the spin-lattice and the gaussian spin-echo decay rates (1/T_1 and 1/T_{2G}) and their ratio all show good quantitative agreement. Our results demonstrate the importance of the logarithmic corrections in the analysis of experimental data for quasi-1D systems and indicate that the dynamics of Sr_2CuO_3 is well described by a S=1/2 one-dimensional Heisenberg model with a nearest neighbor exchange.

S. Korshunov

T. Ghosh, K. Machida

The work by T. K. Ghosh and K. Machida [Phys. Rev. A 73, 013613 (2006) and cond-mat/0510160] on the sound velocity in a cylindrically confined Fermi superfluid obeying a power-law equation of state is shown to make use of an improper projection of the sound wave equation. This inaccuracy fully accounts for the difference between their results and those previously reported by Capuzzi et al. [Phys. Rev. A 73, 021603(R) (2006) and cond-mat/0509323]. In this Comment, we show that both approaches lead exactly to the same result when the correct weight function is used in the projection. Plots of the correct behavior of the phonon and monopole-mode spectra in the BCS and unitary limits and in the BEC regime are also shown.

J. Chu, C. Chiang, H. Wijaya et al.

M. Cazalilla, J. Marston

Reply to the Comment of Luo, Xiang, and Wang, cond-mat/0212580.

V. Gurarie, E. Rezayi

We continue the program started in cond-mat/9809384 and explain the statistics of the excitations for the generalizations of the paired states in the quantum Hall effect in terms of the parafermion statistics. We show that these excitations behave as combinations of bosons and parafermions. That generalizes the prior treatment of the paired (Pfaffian) state where the excitations behave as combinations of bosons and fermions. We explain what it means, from a quantum mechanical point of view, for a particle to be a `parafermion' rather than a boson or a fermion and work through several explicit examples. The resulting multiplets coincide exactly with the angular momentum multiplets found numerically for the $k+1$ particle interaction Hamiltonian on a sphere. We also present a proof that the wave functions found in cond-mat/9809384 are indeed the correlation functions of the parafermion conformal field theory.

Mj Davis, C. Gardiner

We extend the earlier model of condensate growth of Davis et al (Davis M J, Gardiner C W and Ballagh R J 2000 Phys. Rev. A 62 063608) to include the effect of gravity in a magnetic trap. We carry out calculations to model the experiment reported by Kohl et al (Kohl M, Davis M J, Gardiner C W, Hansch T and Esslinger T 2001 Preprint cond-mat/0106642) who study the formation of a rubidium Bose-Einstein condensate for a range of evaporative cooling parameters. We find that, in the regime where our model is valid, the theoretical curves agree with all the experimental data with no fitting parameters. However, for the slowest cooling of the gas the theoretical curve deviates significantly from the experimental curves. It is possible that this discrepancy may be related to the formation of a quasicondensate.

Y. Naidyuk, I. Yanson, L. V. Tyutrina et al.

We have analyzed about a hundred voltage-dependent differential resistance dV/dI(V) curves of metallic point contacts between c-axis-oriented MgB2 thin film and Ag, which exhibit clear Andreev reflection features connected with the superconducting gap. About one half of the curves show the presence of a second larger gap. The histogram of the double gap distribution reveals distinct maxima at 2.4 and 7 meV, while curves with single-gap features result in a more broad maximum at 3.5 meV. The double-gap distribution is in qualitative agreement with the distribution of gap values over the Fermi surface calculated by H. J. Choi et al. (cond-mat/0111183). The data unequivocally show the presence of two gaps: ΔS=2.45±0.15 meV and ΔL=7.0±0.45 meV in MgB2 with the gap ratio ΔL/ΔS=2.85±0.15. Our observations further prove a widely discussed multigap scenario for MgB2, where two distinct gaps are seen in the clean limit, while a single averaged gap is present in the dirty one.

E. Calzetta, B. Hu

(May 18, 2003, second version of cond-mat/0207289 deposited in arXiv on July 11, 2002. umdpp02-61)AbstractWe analyzethe phenomena ofcondensatecollapse, asdescribed byDonley et al [1, 2], by focusingon the behavior of excitations or fluctuations above the condensate, as driven by the dynamics ofthe condensate, rather than the dynamics of the condensate alone or the kinetics of the atoms. Thedynamics of the condensate squeezes and amplifies the quantum excitations, mixing the positiveand negative frequency components of their wave functions thereby creating particles which appearas bursts and jets. By analyzing the changing amplitude and particle content of these excitations,our simple physical picture explains well the overall features of the collapse phenomena and provideexcellent quantitative fits with experimental data on several aspects, such as the scaling behavior ofthe collapse time and the amount of particles in the jet. The predictions of the bursts at this levelof approximation is less than satisfactory but may be improved on by including the backreactionof the excitations on the condensate. The mechanism behind the dominant effect – parametricamplification of vacuum fluctuations and freezing of modes outside of horizon – is similar to that ofcosmological particle creation and structure formation in a rapid quench (which is fundamentallydifferent from Hawking radiation in black holes). This shows that BEC dynamics is a promisingvenue for doing ‘laboratory cosmology’.

M. Valín-Rodríguez, A. Puente, L. Serra

4 pages (final publisher version), 9 pages, 3 figures (attached post-print version).-- PACS nrs.: 73.21.La, 73.21.-b.-- Pre-print version available at ArXiv: http://arxiv.org/abs/cond-mat/0311077.

M. Bouville, R. Ahluwalia

Materials which can undergo slow diffusive transformations as well as fast displacive transformations are studied using the phase-field method. The model captures the essential features of the time-temperature-transformation (TTT) diagrams, continuous cooling transformation (CCT) diagrams, and microstructure formation of these alloys. In some materials systems there can exist an intrinsic volume change associated with these transformations. We show that these coherency strains can stabilize mixed microstructures (such as retained austenite-martensite and pearlite-martensite mixtures) by an interplay between diffusive and displacive mechanisms, which can alter TTT and CCT diagrams. Depending on the conditions there can be competitive or cooperative nucleation of the two kinds of phases. The model also shows that small differences in volume changes can have noticeable effects on the early stages of martensite formation and on the resulting microstructures. -- Long version of cond-mat/0605577 -- Keywords: Ginzburg-Landau, martensite, pearlite, spinodal decomposition, shape memory, microstructures, TTT diagram, CCT diagram, elastic compatibility