Quench dynamics and nonequilibrium phase diagram of the bose-hubbard model

We investigate the time evolution of correlations in the Bose-Hubbard model following a quench from the superfluid to the Mott insulator. For large values of the final interaction strength the system approaches a distinctly nonequilibrium steady state that bears strong memory of the initial conditions. In contrast, when the final interaction strength is comparable to the hopping, the correlations are rather well approximated by those at thermal equilibrium. The existence of two distinct nonequilibrium regimes is surprising given the nonintegrability of the Bose-Hubbard model. We relate this phenomenon to the role of quasiparticle interactions in the Mott insulator.     

Spin-charge separation in cold fermi gases: a real time analysis

Using the adaptive time-dependent density-matrix renormalization group method for the 1D Hubbard model, the splitting of local perturbations into separate wave packets carrying charge and spin is observed in real time. We show the robustness of this separation beyond the low-energy Luttinger liquid theory by studying the time evolution of single particle excitations and density wave packets. A striking signature of spin-charge separation is found in 1D cold Fermi gases in a harmonic trap at the boundary between liquid and Mott-insulating phases. We give quantitative estimates for an experimental observation of spin-charge separation in an array of atomic wires.     

Chaos in variable stars: Topological analysis of W Vir model pulsations

The topological characterization of chaos is applied to the irregular pulsations of a model for a star of the W Virginis type, computed with a state-of-the-art numerical hydrodynamical code. The banded W Vir attractor is found to possess an additional twist when compared to the Rossler band. It is shown that the stellar light-curve contains the same dynamical information about the attractor as the stellar radius or as the radial velocity variations. (c) 1996 American Institute of Physics.     

Electron spin resonance shift in spin ladder compounds

We analyze the effects of different coupling anisotropies in a spin-1/2 ladder on the electron spin resonance (ESR) shift. Combining a perturbative expression in the anisotropies with density matrix renormalization group computation of the short range correlations at finite temperature, we provide the full temperature and magnetic field evolution of the ESR paramagnetic shift. We show that for well chosen parameters the ESR shift can be in principle used to extract quantitatively the anisotropies and, as an example, discuss the material BPCB.     

Spectral and thermodynamic properties of a strong-leg quantum spin ladder

The strong-leg S=1/2 Heisenberg spin ladder system (C(7)H(10)N)(2)CuBr(4) is investigated using density matrix renormalization group calculations, inelastic neutron scattering, and bulk magnetothermodynamic measurements. Measurements showed qualitative differences compared to the strong-rung case. A long-lived two-triplon bound state is confirmed to persist across most of the Brillouin zone in a zero field. In applied fields, in the Tomonaga-Luttinger spin-liquid phase, elementary excitations are attractive, rather than repulsive. In the presence of weak interladder interactions, the strong-leg system is considerably more prone to three-dimensional ordering.     

Dipolar bosons in a planar array of one-dimensional tubes

We investigate bosonic atoms or molecules interacting via dipolar interactions in a planar array of one-dimensional tubes. We consider the situation in which the dipoles are oriented perpendicular to the tubes by an external field. We find various quantum phases reaching from a "sliding Luttinger liquid" phase to a two-dimensional charge density wave ordered phase. Two different kinds of charge density wave order occur: a stripe phase in which the bosons in different tubes are aligned and a checkerboard phase. We further point out how to distinguish the occurring phases experimentally.     

Controllable manipulation of crystallinity and morphology of aluminium surfaces using high intensity ultrasound

High intensity ultrasound (HIUS) provides highly non-equilibrium condition for metal processing. Controllable manipulation of crystallinity and morphology of metal coatings is important for different applications including catalysis and corrosion protection. Investigation of effects of HIUS in different sonication media on microstructure and morphology of aluminium (Al) layers showed that HIUS can cause melting and recrystallization of Al. Due to high cooling rate the grain size of Al can be reduced. Ultrasonically induced structure refinement could potentially be used for enhancement of mechanical properties of coatings. If ultrasonically generated temperature is not high enough for metal melting, temperature induced atomic diffusion leads to grain growth, segregation and fragmentation of Al layers and, thus, the formation of attractive for catalytic application increased surface area.     

The critical position for elastic electron scattering in neon

A measurement of the electron energy and scattering angle where the differential cross section for elastic electron scattering by neon atoms reaches its smallest value is reported. This is compared with our derivations of the critical position from seven theoretical models and from two sets of phase shifts obtained by analysis of experimental data. The latter show poor agreement with our value. The theoretical critical positions tend to lie at a lower energy and angle than our measurement, but theR-matrix calculations of Blum and Burke yield a critical position closest to it.     

Slow quench dynamics of a one-dimensional Bose gas confined to an optical lattice

We analyze the effect of a linear time variation of the interaction strength on a trapped one-dimensional Bose gas confined to an optical lattice. The evolution of different observables such as the experimentally accessible on site particle distribution are studied as a function of the ramp time by using time-dependent numerical techniques. We find that the dynamics of a trapped system typically displays two regimes: For long ramp times, the dynamics is governed by density redistribution, while at short ramp times, local dynamics dominates as the evolution is identical to that of an homogeneous system. In the homogeneous limit, we also discuss the nontrivial scaling of the energy absorbed with the ramp time.