Recent Publications

Tchavdar Todorov

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  1. Title: Nonconservative dynamics in long atomic wires

    Author(s): Cunningham B., Todorov T.N., Dundas D.

    Physical Review B, 90, pp. 115430 - (24 September 2014)

    doi: 10.1103/PhysRevB.90.115430
    Abstract



    The effect of nonconservative current-induced forces on the ions in a defect-free metallic nanowire is investigated using both steady-state calculations and dynamical simulations. Nonconservative forces were found to have a major influence on the ion dynamics in these systems, but their role in increasing the kinetic energy of the ions decreases with increasing system length. The results illustrate the importance of nonconservative effects in short nanowires and the scaling of these effects with system size. The dependence on bias and ion mass can be understood with the help of a simple pen and paper model. This material highlights the benefit of simple preliminary steady-state calculations in anticipating aspects of brute-force dynamical simulations, and provides rule of thumb criteria for the design of stable quantum wires.

  2. Title: Current-induced forces: a simple derivation

    Author(s): Todorov T.N., Dundas D., Lü J., Brandbyge M., Hedegård P.

    European Journal of Physics, 35, No. 6, pp. 065004- (02 September 2014)

    doi: 10.1088/0143-0807/35/6/065004
    Abstract



    We revisit the problem of forces on atoms under current in nanoscale conductors. We derive and discuss the five principal kinds of force under steady-state conditions from a simple standpoint that—with the help of background literature—should be accessible to physics undergraduates. The discussion aims at combining methodology with an emphasis on the underlying physics through examples. We discuss and compare two forces present only under current—the non-conservative electron wind force and a Lorentz-like velocity-dependent force. It is shown that in metallic nanowires both display significant features at the wire surface, making it a candidate for the nucleation of current-driven structural transformations and failure. Finally we discuss the problem of force noise and the limitations of Ehrenfest dynamics