Quantum dynamics in atomic wires
Supervisors: Dr Tchavdar Todorov, Dr Daniel Dundas and Prof. J Kohanoff
Summary
Every morning we boil the kettle and make toast. In winter we'd first turn on
the electric heater to take the chill out of the air. In all these cases we are
getting heat. But where does it come from? Amazingly its agents are the tiny
particles that carry current, and bind atoms together: the electrons. When
electrical current is driven through a wire, the current-carrying electrons
"slam" into the atomic nuclei. (It is a bit more subtle than that but this is
the basic idea.) The nuclei, though much heavier, respond and pick up small
bits of kinetic energy. Over time, this makes them vibrate more and more
energetically: the result is what we perceive as heating.
But ordinary wires are not the only place where this happens. Experimentalists
can now make and study the smallest possible conductors in nature: atomic and
molecular wires, such as atomic chains, carbon nanotubes and molecular
junctions.
Current flow in these systems is a fascinating problem, for both experiment
and theory.
We are interested in this problem as theorists. Transport in nanoscale
conductors has many aspects. One of the hardest - but also most interesting
and topical - is how current flow in these systems drives atomic motion in
them.
Two key processes involved are Joule heating (the nanoscale analogue of what
happens in the toaster) and a novel effect, from the past couple of years:
the atomic-scale analogue of how a stream drives a watermill. We have worked
on both problems, making advances using our own methods [1,2].
The theory involved is challenging and can be formulated at a variety of
levels, depending on what aspects of the interaction between current-carrying
electrons and atomic motion we wish to capture. A central issue is that atomic
motion, fundamentally, is a dynamical quantum problem, like the motion of
electrons.
Both the dynamical simulation of Joule heating and of the atomic-waterwheel
effect remain areas of ongoing theoretical development. In this project we
wish to explore a recent idea for a simple but promising method for quantum
electron-nuclear dynamics and apply it to both problems.
The project is likely to involve a balanced and flexible combination of theory
and computational work. It is an attractive problem, in an exciting field,
offering training in important areas: transport theory, electron-nuclear
dynamics, numerical modelling and simulation.
References:
[1] E. J. McEniry, D. R. Bowler, D. Dundas, A. P. Horsfield, C. G. Sanchez and T. N. Todorov: Dynamical simulation of inelastic quantum transport, Journal of Physics: Condensed Matter 19 (2007) 196201
[2] D. Dundas, E. J. McEniry and T. N. Todorov: Current-driven atomic waterwheels, Nature Nanotechnology 4 (2009) 99
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