arXiv subjects

Hans Fangohr

Publications and source records attributed to Hans Fangohr.

76 records · Page 5Linked to original sources

arXiv2002

Vortex matter in layered superconductors without Josephson coupling: numerical simulations within a mean-field approach

We study vortex matter in layered superconductors in the limit of zero Josephson coupling. The long range of the interaction between pancake vortices in the c-direction allows us to employ a mean-field method: all attractive inter-layer interactions are reduced to an effective substrate potential, which pancakes experience in addition to the same-layer pancake repulsion. We perform numerical simulations of this mean-field model using two independent numerical implementations with different simulation methods (Monte-Carlo sampling and Langevin molecular dynamics). The substrate potential is updated self-consistently from the averaged pancake density. Depending on temperature, this potential converges to a periodic profile (crystal) or vanishes (liquid). We compute thermodynamic properties of the system, such as the melting line, the instability line of the crystal, and the entropy jump across the melting transition. The simulation results are in good agreement with approximate analytical calculations.

cond-mat.supr-con↗

arXiv2001

Vortex dynamics in two-dimensional systems at high driving forces

We study numerically the dynamics of two-dimensional vortex systems at zero temperature. In addition to pinned states and turbulent plastic flow, we find motion of vortices in rough channels along the direction of the driving force. In this decoupled channel regime we demonstrate how topological defects mediate the phase slip of different channels moving with different velocities. We thus provide important confirmation of recent analytical work describing vortex dynamics at high driving forces such as the moving glass theory of Giamarchi and Le Doussal. For the largest driving forces we find that the channels couple and observe elastic motion.

cond-mat↗

arXiv2000

Critical Transverse Forces in Weakly Pinned Driven Vortex Systems

We present simulation results of the moving Bragg glass regime of a driven two-dimensional vortex system in the presence of a smoothly varying weak pinning potential. We study the critical transverse force and (i) demonstrate that it can be an order of magnitude larger than previous estimates (ii) show that it is still observable when the system is driven along low higher-order lattice vectors. We confirm theoretical predictions that the critical transverse force is the order parameter of the so-called moving glass phase, and provide data to support experimentalists verifying the existence of a critical transverse force.

cond-mat.supr-con↗

arXiv2000

Efficient Methods for Handling Long-Range Forces in Particle-Particle Simulations

A number of problems arise when long-range forces, such as those governed by Bessel functions, are used in particle-particle simulations. If a simple cut-off for the interaction is used, the system may find an equilibrium configuration at zero temperature that is not a regular lattice yet has an energy lower than the theoretically predicted minimum for the physical system. We demonstrate two methods to overcome these problems in Monte Carlo and molecular dynamics simulations. The first uses a smoothed potential to truncate the interaction in a single unit cell: this is appropriate for phenomenological characterisations, but may be applied to any potential. The second is a new method for summing the unmodified potential in an infinitely tiled periodic system, which is in excess of 20,000 times faster than previous naive methods which add periodic images in shells of increasing radius: this is suitable for quantitative studies. Finally we show that numerical experiments which do not handle the long-range force carefully may give misleading results: both of our proposed methods overcome these problems.

physics.comp-ph↗