arXiv subjects

Kipton Barros

Publications and source records attributed to Kipton Barros.

79 records · Page 5Linked to original sources

arXiv2013

Liquid to solid nucleation via onion structure droplets

We study homogeneous nucleation from a deeply quenched metastable liquid to a spatially modulated phase. We find, for a general class of density functional theories, that the universally favored nucleating droplet in dimensions $d \geq 3$ is spherically symmetric with radial modulations resembling the layers of an onion. The existence of this droplet has important implications for systems with effective long-range interactions, and potentially applies to polymers, plasmas, and metals.

cond-mat.stat-mech↗

arXiv2013

Efficient Langevin Simulation of Coupled Classical Fields and Fermions

We introduce an efficient Langevin method to study bilinear Fermionic Hamiltonians interacting with classical fields. Our method is suitable for very large systems and offers high accuracy. To demonstrate the method, we study complex non-coplanar chiral spin textures on the triangular Kondo lattice model. We also explore non-equilibrium mesoscale physics such as chiral domain coarsening and Z2 vortex annihilation.

cond-mat.stat-mech↗

arXiv2011

Freezing into Stripe States in Two-Dimensional Ferromagnets and Crossing Probabilities in Critical Percolation

When a two-dimensional Ising ferromagnet is quenched from above the critical temperature to zero temperature, the system eventually converges to either a ground state (all spins aligned) or an infinitely long-lived metastable stripe state. By applying results from percolation theory, we analytically determine the probability to reach the stripe state as a function of the aspect ratio and the form of the boundary conditions. These predictions agree with simulation results. Our approach generally applies to coarsening dynamics of non-conserved scalar fields in two dimensions.

cond-mat.stat-mech↗

arXiv2008

Early time kinetics of systems with spatial symmetry breaking

In this paper we present a study of the early stages of unstable state evolution of systems with spatial symmetry changes. In contrast to the early time linear theory of unstable evolution described by Cahn, Hilliard, and Cook, we develop a generalized theory that predicts two distinct stages of the early evolution for symmetry breaking phase transitions. In the first stage the dynamics is dominated by symmetry preserving evolution. In the second stage, which shares some characteristics with the Cahn-Hilliard-Cook theory, noise driven fluctuations break the symmetry of the initial phase on a time scale which is large compared to the first stage for systems with long interaction ranges. To test the theory we present the results of numerical simulations of the initial evolution of a long-range antiferromagnetic Ising model quenched into an unstable region. We investigate two types of symmetry breaking transitions in this system: disorder-to-order and order-to-order transitions. For the order-to-order case, the Fourier modes evolve as a linear combination of exponentially growing or decaying terms with different time scales.

cond-mat.stat-mech↗

arXiv2008

Blasting through lattice calculations using CUDA

Modern graphics hardware is designed for highly parallel numerical tasks and provides significant cost and performance benefits. Graphics hardware vendors are now making available development tools to support general purpose high performance computing. Nvidia's CUDA platform, in particular, offers direct access to graphics hardware through a programming language similar to C. Using the CUDA platform we have implemented a Wilson-Dirac operator which runs at an effective 68 Gflops on the Tesla C870. The recently released GeForce GTX 280 runs this same code at 92 Gflops, and we expect further improvement pending code optimization.

hep-lat↗

arXiv2008

Beyond Cahn-Hilliard-Cook: Early time behavior of symmetry breaking phase transition kinetics

We extend the early time ordering theory of Cahn, Hilliard, and Cook (CHC) so that our generalized theory applies to solid-to-solid transitions. Our theory involves spatial symmetry breaking (the initial phase contains a symmetry not present in the final phase). The predictions of our generalization differ from those of the CHC theory in two important ways: exponential growth does not begin immediately following the quench, and the objects that grow exponentially are not necessarily Fourier modes. Our theory is consistent with simulation results for the long-range antiferromagnetic Ising model.

cond-mat.stat-mech↗

arXiv2007

Approaching equilibrium and the distribution of clusters

We investigate the approach to stable and metastable equilibrium in Ising models using a cluster representation. The distribution of nucleation times is determined using the Metropolis algorithm and the corresponding $ϕ^{4}$ model using Langevin dynamics. We find that the nucleation rate is suppressed at early times even after global variables such as the magnetization and energy have apparently reached their time independent values. The mean number of clusters whose size is comparable to the size of the nucleating droplet becomes time independent at about the same time that the nucleation rate reaches its constant value. We also find subtle structural differences between the nucleating droplets formed before and after apparent metastable equilibrium has been established.

cond-mat.stat-mech↗