Hasil untuk "cond-mat"

Y. Kafri, D. Mukamel, L. Peliti

M. D. Jongh

This thesis gives an extension for the Density Matrix Renormalisation Group (DMRG) to two dimensions and described a newly developed combination of the DMRG and a Green Function Monte Carlo simulation (GFMC). The first two chapters focus on the DMRG method. The properties are reviewed and it is shown that good quality results can be obtained for two-dimensional systems through finite-size scaling. In the third and fourth chapter the properties of the two-dimensional frustrated Heisenberg model are analysed using a similar combination of DMRG and finite-size scaling. The final chapter presents the combination of the DMRG and GFMC with Stochastic Reconfiguration (Sorella, Capriotti cond-mat/9902211) We find an intermediate phase between Neel and collinear long-range order. This phase shows spatial inhomogeneities with a tendency towards plaquette formation.

A. Bhattacharya, I. Žutić, O. Valls et al.

In a recent Letter (Phys. Rev. Lett. 81, p.5640 (1998), cond-mat/9808249 v3), it was suggested that nonlocal effects may prevent observation of the nonlinear Meissner effect in YBCO. We argue that this claim is incorrect with regards to measurements of the nonlinear transverse magnetic moment, and that the most likely reason for a null result lies elsewhere.

M. V. Rossum

In my thesis I study mesoscopic corrections on diffuse transport. I first describe the diffuse transport of light, using the scalar approximation and the radiative transfer approach. Next, I focus on the correlations in transmission, I discuss the so called C_1, C_2, C_3 decomposition and calculate each term in detail. Finally, I discuss the full distribution functions in the transmission. Many references and figures are included. Note, however, that much of the work was already published or is present on the cond-mat archive. A limited number is available as hardcopy on request (vrossum@phys.uva.nl) else 132 pages Postscript.

S. Borisenko, A. Kordyuk, A. Koitzsch et al.

In a recent preprint Campuzano et al.(cond-mat/0309402), have questioned the validity of our ARPES results (cond-mat/0305179) contradicting the interpretation of earlier photoemission experiments in terms of the time-reversal symmetry breaking in Bi2212. Here we highlight the principal results of our study and refute all the criticism.

I. Mirebeau, M. Hennion, H. Casalta et al.

Original paper from Mirebeau et al. PRL 83, 628, 1999 Comment from W. Bao et al (cond-mat/0008042, 2 Aug 2000 submitted to PRL, updated on 1 sep 2000

C. Nedelcu, A. Kolezhuk, H. Mikeska

A model of a two-leg spin-S ladder with two additional frustrating diagonal exchange couplings JD , JD ´ is studied within the framework of the nonlinear sigma model approach. The phase diagram has a rich structure and contains 2S gapless phase boundaries which split off the boundary to the fully saturated ferromagnetic phase when JD and JD ´ become different. For the S = 1/2 case, the phase boundary is identified as separating two topologically distinct Haldane-type phases as discussed recently by Kim and co-workers (Kim E H, Fath G, Solyom J and Scalapino D J 1999 e-print cond-mat/9910023).

C. Burgess, C. Lutken

We construct the low-energy effective theory for the SO(5) model of high-Tc superconductivity, recently proposed by S.C. Zhang (cond-mat/9610140). This permits us to develop a systematic expansion for low-energy observables in powers of the small symmetrybreaking interactions. The approximate SO(5) symmetry predicts relations amongst these observables, which are model-independent consequences of Zhang’s proposed symmetrybreaking pattern.

A. Travesset

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.

A. Cuccoli, A. Fubini, V. Tognetti et al.

The effects of quantum and thermal fluctuations upon the fringe structure predicted to be observable in the momentum distribution of coupled Bole-Einstein condensates are studied by the effective-potential method. For a double-well trap, the coherence factor recently introduced by Pitaevskii and Stringari (e-print cond-mat/ 0104458) is calculated using the effective potential approach and is found in good agreement with their result. The calculations are extended to the case of a one-dimensional array of condensates, showing that quantum effects are essentially described through a simple renormalization of the energy scale in the classical analytical expression for the fringe structure. The consequences for the experimental observability are discussed.

G. Gunaratne

Disordered networks of fragile elastic elements have been proposed as a model of inner porous regions of large bones [Gunaratne et.al., cond-mat/0009221, this http URL]. It is shown that the ratio $\Gamma$ of responses of such a network to static and periodic strain can be used to estimate its ultimate (or breaking) stress. Since bone fracture in older adults results from the weakening of porous bone, we discuss the possibility of using $\Gamma$ as a non-invasive diagnostic of osteoporotic bone.

F. Essler, F. Gohmann, V. Korepin

We comment on the preprint cond-mat/9805103 by D. Braak and N. Andrei \cite{BrAn98}. We point out that the ``new'' Bethe Ansatz equations presented in \cite{BrAn98} are identical to the Bethe equations for strings introduced by M. Takahashi for the description of thermodynamics in 1972 \cite{Takahashi72}. Some physics suggested in \cite{BrAn98} is incorrect. In particular, all former conclusions made on the basis of the string Bethe equations remain valid.

M. Reznikov, U. Sivan

The paper by A. A. Shashkin et al. [cond-mat/0409100] reports measurements of the thermodynamic magnetization of two-dimensional electrons in silicon. Although the experimental data is very similar to that reported by us more then two years ago, the authors arrive at an opposite conclusion regarding the spin susceptibility "critical behavior" and spin instability in the vicinity of the metal-insulator transition. We show that this interpretation is based on a flawed analysis of the experimental data.

Y. Barash, A. A. Svidzinskii

J. Denlinger, J. Clack, J. Allen et al.

This paper has been withdrawn by the authors due to new theoretical evidence and experimental proof that the semiconducting bandgap reported in this paper and ascribed to a surface region is in fact a bulk property of divalent hexaborides. As reported in J. D. Denlinger et al., cond-mat/0107429, which supercedes this paper, bulk-sensitive boron K-edge soft x-ray emission provides a complementary confirmation of the X-point band gap identified by angle-resolved photoemission.

A. Bray, M. .. Moore

This paper has been replaced by cond-mat/0309113

M.Hotta

This paper has been withdrawn by the author and the content is merged into a new paper: H-Theorem and Generalized Entropy Composition with Different q Indices: cond-mat/9912454.

V. Gurarie, A. Zee

This preprint has been withdrawn as crucial errors have been discovered in the papers it has referred to. It is now superseded by cond-mat/9807391.

I. Suslov

Answer to cond-mat/0106005 and cond-mat/0106006 and additional notes are given concerning to my previous comment (cond-mat/0105324).

A. Lima, T. Penna, P. Oliveira

This is a reply to the comment by M. Kastner and M. Promberger on the paper published in J. Stat. Phys.99:691 (2000) and also in Cond-Mat 0002176. We show that all their criticisms do not apply.