Searcharxiv⌕ Search

arXiv subjects

M. D. Grynberg

Publications and source records attributed to M. D. Grynberg.

29 records · Page 2Linked to original sources
arXiv2001

From classical to quantum Kagome antiferromagnet in a magnetic field

We study the magnetic properties of the Kagome antiferromagnet going from the classical limit to the deep quantum regime of spin 1/2 systems. In all the cases there are special values for the magnetization, 1/3 in particular, in which a singular behavior is observed to occur in both the classical and quantum cases. We show clear evidence for a magnetization plateau for the spin 1/2 case in a wide range of XXZ anisotropies and for the occurrence of quantum order by disorder effects.

cond-mat.str-el↗
arXiv2001

Quasi-periodic spin chains in a magnetic field

We study the interplay between a (quasi) periodic coupling array and an external magnetic field in a spin-1/2 XXZ chain. A new class of magnetization plateaux are obtained by means of Abelian bosonization methods which give rise to a sufficient quantization condition. The investigation of magnetic phase diagrams via exact diagonalization of finite clusters finds a complete agreement with the continuum treatment in a variety of situations.

cond-mat.str-el↗
arXiv2001

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.

cond-mat.stat-mech↗
arXiv2000

Random bond XXZ chains with modulated couplings

The magnetization behavior of q-periodic antiferromagnetic spin 1/2 Heisenberg chains under uniform magnetic fields is investigated in a background of disorder exchange distributions. By means of both real space decimation procedures and numerical diagonalizations in XX chains, it is found that for binary disorder the magnetization exhibits wide plateaux at values of 1+2(p-1)/q, where p is the disorder strength. In contrast, no spin gaps are observed in the presence of continuous exchange distributions. We also study the magnetic susceptibility at low magnetic fields. For odd q-modulations the susceptibility exhibits a universal singularity, whereas for q even it displays a non-universal power law behavior depending on the parameters of the distribution.

cond-mat.str-el↗
arXiv2000

Magnetization plateaux in dimerized spin ladder arrays

We investigate the ground state magnetization plateaux appearing in spin 1/2 two-leg ladders built up from dimerized antiferromagnetic Heisenberg chains and dimerized zig-zag interchain couplings. Using both Abelian bosonization and Lanczos methods we find that the system yields rather unusual plateaux and exhibits massive and massless phases for specific choices or ``tuning'' of exchange interactions. The relevance of this behavior in the study of NH_4CuCl_3 is discussed.

cond-mat↗
arXiv1999

Diffusion in disordered lattices and related Heisenberg ferromagnets

We study the diffusion of classical hard-core particles in disordered lattices within the formalism of a quantum spin representation. This analogy enables an exact treatment of non-instantaneous correlation functions at finite particle densities in terms of single spin excitations in disordered ferromagnetic backgrounds. Applications to diluted chains and percolation clusters are discussed. It is found that density fluctuations in the former exhibit a stretched exponential decay while an anomalous power law asymptotic decay is conjectured for the latter.

cond-mat.stat-mech↗
arXiv1999

Massive and Massless Behavior in Dimerized Spin Ladders

We investigate the conditions under which a gap vanishes in the spectrum of dimerized coupled spin-1/2 chains by means of Abelian bosonization and Lanczos diagonalization techniques. Although both interchain ($J'$) and dimerization ($δ$) couplings favor a gapful phase, it is shown that a suitable choice of these interactions yields massless spin excitations. We also discuss the influence of different arrays of relative dimerization on the appearance of non-trivial magnetization plateaus.

cond-mat.str-el↗
arXiv1998

Non-universal dynamics of staggered non-equilibrium particle systems and Ising chains

Non-universal dynamics is shown to occur in a one-dimensional non-equilibrium system of hard-core particles. The stochastic processes included are pair creation and annihilation (with rates e and e') and symmetric hopping rates which alternate from one bond to the next (Pa, Pb). A dynamical scaling relation between the relaxation time and the correlation length in the steady state is derived in a simple way for the case e' > Pa >> Pb >> e. We find that the dynamical exponent takes the non-universal value z = 2 ln(e'/e)/ln[(Pb e')/(Pa e)]. For the special condition e + e'= Pa + Pb, where the stochastic system is in principle soluble by reduction to a free fermion system, the model is mapped to the Glauber dynamics of an Ising chain with alternating ferromagnetic bonds of values J1 and J2, in contact with a quantum thermal bath. The full time dependence of the space-dependent magnetization and of the equal time spin-spin correlation function are studied by writing the master equation for this system in the quantum Hamiltonian formalism. In particular we obtain the dispersion relations and rigorously confirm the results obtained for the correlation length and for the dynamical exponent.

cond-mat.stat-mech↗
arXiv1998

Coarsening dynamics of adsorption processes with diffusional relaxation

We investigate the late coarsening stages of one dimensional adsorption processes with diffusional relaxation. The nonequilibrium domain size distribution is studied by means of the field theory associated to the stochastic evolution. An exact asymptotic solution satisfying dynamical scaling is given for cluster sizes smaller than the average domain length. Our results are supported and compared with Monte Carlo simulations.

cond-mat.stat-mech↗
arXiv1992

Fast-diffusion mean-field theory for k-body reactions in one dimension

We derive an improved mean-field approximation for k-body annihilation reactions kA --> inert, for hard-core diffusing particles on a line, annihilating in groups of k neighbors with probability 0 < q <= 1. The hopping and annihilation processes are correlated to mimic chemical reactions. Our new mean-field theory accounts for hard-core particle properties and has a larger region of applicability than the standard chemical rate equation especially for large k values. Criteria for validity of the mean-field theory and its use in phenomenological data fits are derived. Numerical tests are reported for k=3,4,5,6.

cond-mat↗