Breaking of general rotational symmetries by multi-dimensional classical ratchets

We demonstrate that a particle driven by a set of spatially uncorrelated, independent colored noise forces in a bounded, multidimensional potential exhibits rotations that are independent of the initial conditions. We calculate the particle currents in terms of the noise statistics and the potential asymmetries by deriving an n-dimensional Fokker-Planck equation in the small correlation time limit. We analyze a variety of flow patterns for various potential structures, generating various combinations of laminar and rotational flows.Comment: Accepted, Physical Review

Mirror symmetry breaking through an internal degree of freedom leading to directional motion

We analyze here the minimal conditions for directional motion (net flow in phase space) of a molecular motor placed on a mirror-symmetric environment and driven by a center-symmetric and time-periodic force field. The complete characterization of the deterministic limit of the dissipative dynamics of several realizations of this minimal model, reveals a complex structure in the phase diagram in parameter space, with intertwined regions of pinning (closed orbits) and directional motion. This demonstrates that the mirror-symmetry breaking which is needed for directional motion to occur, can operate through an internal degree of freedom coupled to the translational one.Comment: Accepted for publication in Phys. Rev.

Scanning tunneling microscopy

A brief review of the state-of-the-art of scanning tunneling microscopy (STM) is presented with emphasis on materials problems. I shall discuss in particular the variety of materials, environrnents and temperatures that can be investigated. In addition to topographie studies, some examples of STM as local probe are given. It is proposed that STM be increasingly incorporated as a technique for investigation of real materials problems

Stable and metastable reconstructions at the C60/Au(110) interface

The geometric structure of C60 monolayers on Au(110) has been investigated by scanning tunneling microscopy. C60 rearranges the (11̄0) rows of surface Au atoms into several unique new reconstruction patterns, i.e. (1 7 5), (1 7 6) and stepped (1 7 2). The latter two reconstructions are merely metastable. The stable (1 7 5) reconstruction is characterized by only two adsorption sites, in which each C60 molecule has two ridge Au atoms as nearest neighbours. The changes in the Au reconstruction and the tendency to bind to the most reactive surface atoms indicate strong chemical bonding between the substrate and C60