Girija S. Dubey

Numerical simulations of flux-line lattices in layered superconductors

Abstract A model of the effective interaction between the magnetic flux-lines in a layered superconductor is derived from the Lawrence–Doniach model. We show analytically that the intralayer interaction energy can be evaluated using the Ewald summation technique. To illustrate the usefulness of the simulation technique, the isothermal shear modulus c 66 of flux-line lattices with various values of the interlayer coupling strength was obtained with a Langevin dynamics simulation.

Molecular dynamics study of the effect of cooling and heating on the pattern formation and stability of silicon clusters

Molecular dynamics simulations are carried out for silicon clusters to analyze the effect of heating and cooling on their structural properties. The calculations are based on the Kaxiras and Pandey potential which has been derived from a microscopic calculation with the density functional method. Results for the cluster formation are presented for different rates of cooling and heating. Our simulation results clearly show the dependence of the patterns on the cooling and heating rates as well as the way in which these clusters evolve.

Effect of two-body and three-body correlations on the diffusion constant of two-dimensional Coulomb systems in a uniform magnetic field

Abstract We calculate the diffusion constant of a two-dimensional electron gas (2DEG) in a uniform perpendicular external magnetic field using the short-time expansion of the Kubo–Greenwood formula. We model the 2DEG as a one-component plasma. The two-body and three-body correlation functions are obtained from the hypernetted-chain integral equation theory and the Kirkwood superposition approximation, respectively. We compare the diffusion constant at two different temperatures. At the lower temperature, the diffusion constant increases as the magnetic field is increased but decreases with increasing magnetic field at the higher temperature. We compare our results when only two-body correlations are taken into account with those when both two-body and three-body correlations are included. These results may be interpreted as being due to the competition between the magnetic force and the force exerted on the target particle by the surrounding electrons in the 2DEG in the presence of a perpendicular magnetic field.

Two-dimensional Coulomb systems in a uniform magnetic field

Abstract We present molecular dynamics (MD) calculations of the velocity autocorrelation function and the self-diffusion constant of the two-dimensional electron gas in a uniform perpendicular magnetic field.

Isothermal elastic constants of flux-line lattice in layered superconductors

A model of the effective interaction between the magnetic flux-lines in a layered superconductor is derived from the Lawrence–Doniach model. We show analytically that the intralayer interaction energy can be evaluated using the Ewald summation technique. The melting of flux line lattices is studied using Langevin dynamics simulation of the model with various values of interlayer coupling strength and pinning intensities. The thermal fluctuation terms of the isothermal shear modulus are found to increase sharply at the melting transition temperature for systems with or without pinning, while the structural order parameters were close to zero at all temperatures for systems with strong pinning. The melting of the pinned flux-line lattice is discussed in the context of its elastic properties.