7 research outputs found
Shuttling heat across 1D homogenous nonlinear lattices with a Brownian heat motor
We investigate directed thermal heat flux across 1D homogenous nonlinear
lattices when no net thermal bias is present on average. A nonlinear lattice of
Fermi-Pasta-Ulam-type or Lennard-Jones-type system is connected at both ends to
thermal baths which are held at the same temperature on temporal average. We
study two different modulations of the heat bath temperatures, namely: (i) a
symmetric, harmonic ac-driving of temperature of one heat bath only and (ii) a
harmonic mixing drive of temperature acting on both heat baths. While for case
(i) an adiabatic result for the net heat transport can be derived in terms of
the temperature dependent heat conductivity of the nonlinear lattice a similar
such transport approach fails for the harmonic mixing case (ii). Then, for case
(ii), not even the sign of the resulting Brownian motion induced heat flux can
be predicted a priori. A non-vanishing heat flux (including a non-adiabatic
reversal of flux) is detected which is the result of an induced dynamical
symmetry breaking mechanism in conjunction with the nonlinearity of the lattice
dynamics. Computer simulations demonstrate that the heat flux is robust against
an increase of lattice sizes. The observed ratchet effect for such directed
heat currents is quite sizable for our studied class of homogenous nonlinear
lattice structures, thereby making this setup accessible for experimental
implementation and verification.Comment: 9 pages, 10 figures. Phys. Rev. E (in press
Molecular wires acting as quantum heat ratchets
We explore heat transfer in molecular junctions between two leads in the
absence of a finite net thermal bias. The application of an unbiased,
time-periodic temperature modulation of the leads entails a dynamical breaking
of reflection symmetry, such that a directed heat current may emerge (ratchet
effect). In particular, we consider two cases of adiabatically slow driving,
namely (i) periodic temperature modulation of only one lead and (ii)
temperature modulation of both leads with an ac driving that contains a second
harmonic, thus generating harmonic mixing. Both scenarios yield sizeable
directed heat currents which should be detectable with present techniques.
Adding a static thermal bias, allows one to compute the heat current-thermal
load characteristics which includes the ratchet effect of negative thermal bias
with positive-valued heat flow against the thermal bias, up to the thermal
stop-load. The ratchet heat flow in turn generates also an electric current. An
applied electric stop-voltage, yielding effective zero electric current flow,
then mimics a solely heat-ratchet-induced thermopower (``ratchet Seebeck
effect''), although no net thermal bias is acting. Moreover, we find that the
relative phase between the two harmonics in scenario (ii) enables steering the
net heat current into a direction of choice.Comment: 9 pages, 8 figure
Phononics: Manipulating heat flow with electronic analogs and beyond
The form of energy termed heat that typically derives from lattice
vibrations, i.e. the phonons, is usually considered as waste energy and,
moreover, deleterious to information processing. However, with this colloquium,
we attempt to rebut this common view: By use of tailored models we demonstrate
that phonons can be manipulated like electrons and photons can, thus enabling
controlled heat transport. Moreover, we explain that phonons can be put to
beneficial use to carry and process information. In a first part we present
ways to control heat transport and how to process information for physical
systems which are driven by a temperature bias. Particularly, we put forward
the toolkit of familiar electronic analogs for exercising phononics; i.e.
phononic devices which act as thermal diodes, thermal transistors, thermal
logic gates and thermal memories, etc.. These concepts are then put to work to
transport, control and rectify heat in physical realistic nanosystems by
devising practical designs of hybrid nanostructures that permit the operation
of functional phononic devices and, as well, report first experimental
realizations. Next, we discuss yet richer possibilities to manipulate heat flow
by use of time varying thermal bath temperatures or various other external
fields. These give rise to a plenty of intriguing phononic nonequilibrium
phenomena as for example the directed shuttling of heat, a geometrical phase
induced heat pumping, or the phonon Hall effect, that all may find its way into
operation with electronic analogs.Comment: 24 pages, 16 figures, modified title and revised, accepted for
publication in Rev. Mod. Phy