Thermoelectricity
Due to the potential revolutionary impact on
economy and on the global energy challenge, thermoelectric
phenomena have already triggered tremendous research
interests worldwide. Yet available thermoelectric
materials to date still have very poor efficiency as compared
with compressor-based refrigerators. Fundamentally this is
because a comprehensive understanding of electron
transport, heat transport and their interplay is still
lacking. More research efforts should be devoted to
understanding how microscopic chaos and ergodicity,
disorder effects, and local thermalization are connected
with transport phenomena at different scales. We apply
extensively our expertise in nonlinear dynamics, complex
systems and statistical mechanics, our purpose being to
gain a better understanding of the physical mechanisms
which might lead to higher thermoelectric efficiencies.
Systems
with broken time-reversal symmetry
Three-dot model (left) for which the Seebeck and the Peltier coefficients are not symmetric
We have shown [2] that
for systems with broken time-reversal symmetry,
typically in presence of an applied magnetic field,
the maximum efficiency and the efficiency at
maximum power are both determined by two
parameters: a ``figure of merit'' and an asymmetry
parameter. In contrast to the time-symmetric case,
the figure of merit is bounded from above;
nevertheless the Carnot efficiency can be reached
at lower and lower values of the figure of merit
and far from the strong coupling condition as the
asymmetry parameter increases. Moreover, the
Curzon-Ahlborn limit for efficiency at maximum
power can be overcome within linear response. We
have shown that a weak magnetic field generally
improves either the efficiency of thermoelectric
power generation or of refrigeration, the
efficiencies of the two processes being no longer
equal when a magnetic field is added. Finally, we
have shown [3] that when non-unitary noise effects
are taken into account the thermopower is in
general asymmetric under magnetic field reversal,
even for non-interacting systems. Our findings
have been illustrated in the example of a
three-dot ring structure pierced by an
Aharonov-Bohm flux.
Three-dot model (left) for which the Seebeck and the Peltier coefficients are not symmetric
References
[1] K. Saito, G. Benenti and G. Casati, A microscopic mechanism for increasing thermoelectric efficiency, Chem. Phys. 375, 508 (2010).
[1] K. Saito, G. Benenti and G. Casati, A microscopic mechanism for increasing thermoelectric efficiency, Chem. Phys. 375, 508 (2010).
[2] G. Benenti, K. Saito and G. Casati, Thermodynamic bounds on efficiency for systems with broken time-reversal symmetry, Phys. Rev. Lett. 106, 230602 (2011).
[3] K. Saito, G. Benenti, G. Casati and T. Prosen, Thermopower with broken time-reversal symmetry, Phys. Rev. B 84, 201306(R) (2011).