Hasil untuk "cond-mat"

Zhao Qian, R. Ahuja, C. M. Araujo et al.

M. Eremin, D. Sunyaev

M. Eremin, D. Sunyaev

Using band structure parameters extracted from photoemission data by Yoshida et al., Phys. Rev. B., 2006, we have analyzed the temperature dependence of the superfluid density in overdoped La2-xSrxCuO4. We point out that the temperature behavior 1/λab2 is very sensitive to the ratio 2?0/kBTc and have estimated this quantity, using experimental data obtained previously by Panagopoulos et al., Phys. Rev. B., 1999. We compare the results with those obtained from NMR / NQR (Nuclear Magnetic Resonance / Nuclear Quadrupole Resonance) (Mayer et al., J. Phys, Cond. Mat., 2007) and scanning tunneling spectros-copy (Kato et al., Physica C, 2007) data.

José María Román, Joan Soto

D. Anghel, D. Churochkin

We apply the model introduced in Phys. Rev. B 75, 064202 (2007), cond-mat/0610469, to calculate the anisotropy effect in the interaction of two level systems with phonons in disordered crystals. We particularize our calculations to cubic crystals and compare them with the available experimental data to extract the parameters of the model. With these parameters we calculate the interaction of the dynamical defects in the disordered crystal with phonons (or sound waves) propagating along other crystalographic directions, providing in this way a method to investigate if the anisotropy comes from the two-level systems being preferably oriented in a certain direction or solely from the lattice anisotropy with the two-level systems being isotropically oriented.

G. Beuf

Abstract Extending the Balitsky–Kovchegov (BK) equation independently to running coupling or to fluctuation effects due to pomeron loops is known to lead in both cases to qualitative changes of the traveling-wave asymptotic solutions. In this paper we study the extension of the forward BK equation, including both running coupling and fluctuations effects, extending the method developed for the fixed coupling case [E. Brunet, B. Derrida, A.H. Mueller, S. Munier, Phys. Rev. E 73 (2006) 056126, cond-mat/0512021 ]. We derive the exact asymptotic behavior in rapidity of the probabilistic distribution of the saturation scale.

A. Zheludev, S. Shapiro, Z. Honda et al.

We report the results of elastic and inelastic neutron-scattering experiments on the Haldane-gap quantum antiferromagnet Ni(C 5 D 1 4 N 2 ) 2 N 3 (PF 6 ) performed at mK temperatures in a wide range of magnetic field applied parallel to the S= I spin chains. Even though this geometry is closest to an ideal axially symmetric configuration, the Haldane gap closes at the critical field H c ≃ 4 T, but reopens again at higher fields. The field dependence of the two lowest magnon modes is experimentally studied and the results are compared with the predictions of several theoretical models. We conclude that of several existing theories, only the recently proposed model [Zheludev et al., cond-mat/0301424] is able to reproduce all the features observed experimentally for different field orientations.

V. Karimipour

Within the Matrix Product Formalism we have already introduced a multi-species exclusion process (Phys. Rev. E, 59 (1999) 25, cond-mat/9809193), in which different particles hop with different rates and fast particles stochastically overtake slow ones. In this letter we show that on an open chain, the master equation of this process can be exactly solved via the coordinate Bethe ansatz. It is shown that the N-body S-matrix of this process is factorized into a product of two-body S-matrices, which in turn satisfy the quantum Yang-Baxter equation (QYBE). This solution is, to our knowledge, a new solution of QYBE.

B. Bernevig

Full expressions for finite frequency spin, charge conductivity, and spin susceptibility in Rashba- and Luttinger-type systems are given. Whereas in the Rashba Hamiltonian the spin conductivity has the same frequency dependence as the dielectric polarizability [E. I. Rashba, cond-mat/0404723] and magnetic susceptibility [S. Erlingsson et al., O. Dimitrovacond-mat/0406531; , cond-mat/0407612], the Luttinger case is different. Moreover, for a generalized Rashba-type coupling the three quantities also exhibit different frequency dependencies.

G. Rashedi, Y. Kolesnichenko

Recently, the ‘(p+h)-wave’ form of pairing symmetry has been proposed for the superconductivity in the PrOs4Sb12 compound (Parker et al 2004 Preprint cond-mat/0407254). In the present paper, a stationary Josephson junction as a weak-link between PrOs4Sb12 triplet superconductors is theoretically investigated. The quasiclassical Eilenberger equations are analytically solved. The spin and charge current-phase diagrams are plotted, and the effect of misorientation between crystals on the spin current and spontaneous and Josephson currents is studied. It is found that such experimental investigations of the current-phase diagrams can be used to test the pairing symmetry in the above-mentioned superconductors. It is shown that this apparatus can be applied as a polarizer for the spin current.

Régis Mélin, D. Feinberg

Based on the model of F/S/F trilayer with atomic thickness (see Buzdin A. and Daumens M., cond-mat/0305320, Europhys. Lett., 64 (2003) 510) we discuss the relative roles of pair-breaking and proximity effects, as a function of the exchange field, of disorder and of a finite thickness in the superconducting layer. The exchange field can be small (weak ferromagnets) or large (strong ferromagnets) compared to the superconducting gap. With weak ferromagnets we show the existence of a re-entrant superconducting gap for the F/S/F trilayer with atomic thickness in the parallel alignment (equivalent to the F/S bilayer). Qualitatively small disorder is equivalent to reducing the value of the hopping parameters. In the presence of a finite thickness in the superconducting layer, the superconducting gap in the antiparallel alignment is larger than in the parallel alignment, meaning that pair breaking dominates over the proximity effect.

N. Laflorencie, H. Rieger

We reconsider the random bond antiferromagnetic spin-1/2 chain for weak disorder and demonstrate the existence of crossover length scale x_W that diverges with decreasing strength of the disorder. Recent DMRG calculations [Phys. Rev. Lett. 89, 127202 (2002); cond-mat/0111027] claimed to have found evidence for a non-universal behavior in this model and found no indications of a universal infinite randomness fixed point (IRFP) scenario. We show that these data are not in the asymptotic regime since the system sizes that have been considered are of the same order of magnitude or much smaller than the crossover length x_W. We give a scaling form for the xx-spin-correlation function that takes this crossover length into account and that is compatible with the IRFP scenario and a random singlet phase.

A. Pagnani, G. Parisi, F. Ricci-Tersenghi

K. Hecker, H. Hegger, A. Altland et al.

In their comment cond-mat/9710285 [Phys. Rev. Lett. 80, 5024 (1998)] den Hartog and van Wees (HW) raise objections against our analysis of the experimental data presented in cond-mat/9708162 [Phys. Rev. Lett. 79, 1547 (1997)]. According to HW, we did not account for the quantum phase incoherence introduced by the Niobium compounds of the investigated Nb/Au hybrid samples. Here we show that and why this criticism is not justified. Some difficulties associated with a precise determination of the coherence lengths are discussed. It is discussed why these uncertainties do not have a qualitative impact on the results reported in our paper.

K. Nagaev

We argue that the nearly 1/3 suppression of shot noise in nondegenerate diffusive contacts recently obtained by Gonzalez et al. (cond-mat/9803372) is due to the specific choice of the energy-independent elastic scattering time.

E. Bernardes, J. Schliemann, J. C. Egues et al.

Recently, we have introduced a novel inter-subband-induced spin-orbit (s-o) coupling (cond-mat/0607218) arising in symmetric wells with at least two subbands. This new s-o coupling gives rise to an usual zitterbewegung - i.e. the semiconductor analog to the relativistic trembling motion of electrons - with cycloidal motion without magnetic fields. Here we complement these findings by explicitly deriving expressions for the corresponding zitterbewegung in spin space.

Z. Tsuboi, Minoru Takahashi

We propose a system of nonlinear integral equations (NLIE) which describes the thermodynamics of the U_{q}(\hat{sl(r+1)}) Perk-Schultz model. These NLIE correspond to a trigonometric analogue of our previous result (cond-mat/0212280), and contain only r unknown functions. In particular, they reduce to Takahashi's NLIE for the XXZ spin chain (cond-mat/0010486) if r=1. We also calculate the high temperature expansion of the free energy. In particular for r=1 case, we have succeeded to derive the coefficients of order O((\frac{J}{T})^{99}).

S. D. Makovetskiy, D. N. M. K. N. U. O. R. Electronics, Ukraine et al.

Spatio-temporal dynamics of a deterministic three-level cellular automaton (TLCA) of Zykov-Mikhailov type (Sov. Phys. - Dokl., 1986, Vol.31, No.1, P.51) is studied numerically. Evolution of spatial structures is investigated both for the original Zykov-Mikhailov model (which is applicable to, for example, Belousov-Zhabotinskii chemical reactions) and for proposed by us TLCA, which is a generalization of Zykov-Mikhailov model for the case of two-channel diffusion. Such the TLCA is a minimal model for an excitable medium of microwave phonon laser, called phaser (D. N. Makovetskii, Tech. Phys., 2004, Vol.49, No.2, P.224; cond-mat/0402640). The most interesting observed forms of TLCA dynamics are as follows: (a) spatio-temporal transient chaos in form of highly bottlenecked collective evolution of excitations by rotating spiral waves (RSW) with variable topological charges; (b) competition of left-handed and right-handed RSW with unexpected features, including self-induced alteration of integral effective topological charge; (c) transient chimera states, i.e. coexistence of regular and chaotic domains in TLCA patterns; (d) branching of TLCA states with different symmetry which may lead to full restoring of symmetry of imperfect starting pattern. Phenomena (a) and (c) are directly related to phaser dynamics features observed earlier in real experiments at liquid helium temperatures on corundum crystals doped by iron-group ions. ACM: F.1.1, I.6, J.2; PACS:05.65.+b, 07.05.Tp, 82.20.Wt

R. M'elin, D. Feinberg

Crossed conductance in hybrid Ferromagnet / Superconductor / Ferromagnet (FSF) structures results from the competition between normal transmission and Andreev reflection channels. Crossed Andreev reflection (CAR) and elastic cotunneling (EC) between the ferromagnets are dressed by local Andreev reflections, which play an important role for transparent enough interfaces and in-termediate spin polarizations. This modifies the simple result previously obtained at lowest order, and can explain the sign of the crossed resistances in a recent experiment [D. Beckmann et al. , cond-mat/0404360]. This holds both in the multiterminal hybrid structure model (where phase averaging over the Fermi oscillations is introduced “by hand” within the approximation of a single non local process) and for infinite planar interfaces (where phase averaging naturally results in the microscopic solution with multiple non local processes).

M. Cazalilla

The evolution of correlations in the exactly solvable Luttinger model (a model of interacting fermions in one dimension) after a sudden interaction switch-on is analytically studied. When the model is defined on a finite-size ring, zero-temperature correlations are periodic in time. However, in the thermodynamic limit, the system relaxes algebraically towards a stationary state which is well described, at least for some simple correlation functions, by the generalized Gibbs ensemble recently introduced by Rigol et al. [cond-mat/0604476]. The critical exponent that characterizes the decay of the one-particle correlation function is different from the known equilibrium exponents. Experiments for which these results can be relevant are also discussed.