Revisiting Kawasaki dynamics in one dimension

Critical exponents of the Kawasaki dynamics in the Ising chain are re-examined numerically through the spectrum gap of evolution operators constructed both in spin and domain wall representations. At low temperature regimes the latter provides a rapid finite-size convergence to these exponents, which tend to $z \simeq 3.11$ for instant quenches under ferromagnetic couplings, while approaching to $z \simeq 2$ in the antiferro case. The spin representation complements the evaluation of dynamic exponents at higher temperature scales, where the kinetics still remains slow.Comment: 11 pages, 8 figure

Growth diversity in one dimensional fluctuating interfaces

A set of one dimensional interfaces involving attachment and detachment of $k$-particle neighbors is studied numerically using both large scale simulations and finite size scaling analysis. A labeling algorithm introduced by Barma and Dhar in related spin Hamiltonians enables to characterize the asymptotic behavior of the interface width according to the initial state of the substrate. For equal deposition--evaporation probability rates it is found that in most cases the initial conditions induce regimes of saturated width. In turn, scaling exponents obtained for initially flat interfaces indicate power law growths which depend on $k$. In contrast, for unequal probability rates the interface width exhibits a logarithmic growth for all $k > 1$ regardless of the initial state of the substrate.Comment: Thoroughly extended and corrected version. Typeset in Latex, 20 pages, 7 postscript figure

Low temperature Glauber dynamics under weak competing interactions

We consider the low but nonzero temperature regimes of the Glauber dynamics in a chain of Ising spins with first and second neighbor interactions $J_1,\, J_2$. For $0 < -J_2 / | J_1 | < 1$ it is known that at $T = 0$ the dynamics is both metastable and non-coarsening, while being always ergodic and coarsening in the limit of $T \to 0^+$. Based on finite-size scaling analyses of relaxation times, here we argue that in that latter situation the asymptotic kinetics of small or weakly frustrated $-J_2/ | J_1 |$ ratios is characterized by an almost ballistic dynamic exponent $z \simeq 1.03(2)$ and arbitrarily slow velocities of growth. By contrast, for non-competing interactions the coarsening length scales are estimated to be almost diffusive.Comment: 12 pages, 5 figures (composite). Brief additions and few changes. To appear in Phys. Rev.

Directed diffusion of reconstituting dimers

We discuss dynamical aspects of an asymmetric version of assisted diffusion of hard core particles on a ring studied by G. I. Menon {\it et al.} in J. Stat Phys. {\bf 86}, 1237 (1997). The asymmetry brings in phenomena like kinematic waves and effects of the Kardar-Parisi-Zhang nonlinearity, which combine with the feature of strongly broken ergodicity, a characteristic of the model. A central role is played by a single nonlocal invariant, the irreducible string, whose interplay with the driven motion of reconstituting dimers, arising from the assisted hopping, determines the asymptotic dynamics and scaling regimes. These are investigated both analytically and numerically through sector-dependent mappings to the asymmetric simple exclusion process.Comment: 10 pages, 6 figures. Slight corrections, one added reference. To appear in J. Phys. Cond. Matt. (2007). Special issue on chemical kinetic

Exact multipoint and multitime correlation functions of a one-dimensional model of adsorption and evaporation of dimers

In this work, we provide a method which allows to compute exactly the multipoint and multi-time correlation functions of a one-dimensional stochastic model of dimer adsorption-evaporation with random (uncorrelated) initial states. In particular explicit expressions of the two-point noninstantaneous/instantaneous correlation functions are obtained. The long-time behavior of these expressions is discussed in details and in various physical regimes.Comment: 6 pages, no figur

Ground states of quantum kagome antiferromagnets in a magnetic field

We study the ground state properties of a quantum antiferromagnet in the kagome lattice in the presence of a magnetic field, paying particular attention to the stability of the plateau at magnetization 1/3 of saturation. While the plateau is reinforced by certain deformations of the lattice, like the introduction of structural defect lines and against an Ising anisotropy, ground state correlations are seen to be quite different and the undistorted SU(2) case appears to be rather special.Comment: 3 pages, 3 figures, contribution to the Japanese-French symposium on "Quantum magnetism in spin, charge and orbital systems", Paris 1-4 October 200

Non-linear spectroscopy of rubidium: An undergraduate experiment

In this paper, we describe two complementary non-linear spectroscopy methods which both allow to achieve Doppler-free spectra of atomic gases. First, saturated absorption spectroscopy is used to investigate the structure of the $5{\rm S}_{1/2}\to 5{\rm P}_{3/2}$ transition in rubidium. Using a slightly modified experimental setup, Doppler-free two-photon absorption spectroscopy is then performed on the $5{\rm S}_{1/2}\to 5{\rm D}_{5/2}$ transition in rubidium, leading to accurate measurements of the hyperfine structure of the $5{\rm D}_{5/2}$ energy level. In addition, electric dipole selection rules of the two-photon transition are investigated, first by modifying the polarization of the excitation laser, and then by measuring two-photon absorption spectra when a magnetic field is applied close to the rubidium vapor. All experiments are performed with the same grating-feedback laser diode, providing an opportunity to compare different high resolution spectroscopy methods using a single experimental setup. Such experiments may acquaint students with quantum mechanics selection rules, atomic spectra and Zeeman effect.Comment: 16 pages, 8 figure

Metastable and scaling regimes of a one-dimensional Kawasaki dynamics

We investigate the large-time scaling regimes arising from a variety of metastable structures in a chain of Ising spins with both first- and second-neighbor couplings while subject to a Kawasaki dynamics. Depending on the ratio and sign of these former, different dynamic exponents are suggested by finite-size scaling analyses of relaxation times. At low but nonzero-temperatures these are calculated via exact diagonalizations of the evolution operator in finite chains under several activation barriers. In the absence of metastability the dynamics is always diffusive.Comment: 18 pages, 8 figures. Brief additions. To appear in Phys. Rev.