séminaire 6 juillet 2015
Article mis en ligne le 22 juin 2015
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Séminaire disciplinaire du LIED

Lundi 6 juillet 14h, Salle Luc Valentin (454A)

Giuliano Benenti, Center for Nonlinear and Complex Systems,

Univ. Insubria, Como, and INFN, Milano, Italy

Increasing Thermoelectric Efficiency : A Statistical Mechanics Approach

The understanding of coupled charge and heat transport in complex systems is a fundamental problem, also of practical interest in connection with the challenging task of developing high-performance thermoelectric heat engines and refrigerators, the low efficiency of existing thermoelectric devices being the factor which limits their use. To investigate this problem, we follow an approach which starts from first principles i.e. from the fundamental microscopic dynamical mechanisms which determine the phenomenological laws of heat and particle transport. We compute the basic transport coefficients (isothermal charge conductivity, heat conductivity, thermopower, and Peltier coefficient) starting from the microscopic equations of motion of stylized models, including billiard models and single- or few-level quantum dots. The transport coefficients are computed by means of nonequilibrium simulations (stochastic reservoirs) and the Green-Kubo formula in classical models, while the (multi-terminal) Landauer-Buttiker approach is used for non-interacting quantum systems. We show that for systems with a single relevant constant of motion, notably momentum conservation, the thermoelectric efficiency reaches the Carnot efficiency in the thermodynamic limit. Such general result is illustrated by means of numerical simulations in the case of a diatomic chain of hard-point elastically colliding particles as well as for Coulomb interaction and for a two-dimensional gas of interacting particles.

For systems with broken time-reversal symmetry, we show that the maximum efficiency and the efficiency at maximum power are both determined by two parameters : a generalized figure of merit and an asymmetry parameter, given by the ratio of the thermopowers obtained for opposite directions of the magnetic field. We also discuss the efficiency of a thermal engine working in linear response regime in a multi-terminal configuration. We provide a general definition of local and non-local transport coefficients (electrical and thermal conductances, and thermoelectric powers).

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