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Jonathan WISE presents

 Theory of heat transfer in nanostructures: microscopic and phenomenological approaches

Monday 20 décembre 2021 at 14:30 

 Amphitheatre of the Maison des Magistères (ground floor), 25 avenue des Martyrs, Grenoble 

Lien visio : https://univ-grenoble-alpes-fr.zoom.us/j/98083110410?pwd=TWN2MnZZcm8xWHFUTXVLT2RLN1ZRdz09

Meeting ID : 980 8311 0410
Passcode : 172046

The presentation will be in English.


Abstract :

Spatially separated objects may exchange heat via radiation. The origin of this mechanism is the random thermal motion of charges inside a body that induce electromagnetic fields that behave and interact with other bodies according to Maxwell’s equations and the materials’ electromagnetic response. It has been understood for over 50 years that the nature of the radiative heat transfer is very different for bodies that are far apart than for bodies that are close together. In particular, for bodies that are close together, in the so-called near field, the wave-like character of the electromagnetic fields is significant and evanescent waves may enhance the heat transfer compared to the far field. There is a renewed interest in studies of the near field due to the relatively newfound experimental relevance of the associated small distances, as well as realisations of novel materials and structures with reduced size and/or dimension. In this thesis we provide theoretical contributions to further our understanding of near field radiative heat transfer.

In this work we elucidate the roles played in the radiative heat transfer by key physical ingredients that are common to many systems. First, we study the average heat exchanged by parallel two-dimensional metallic layers modelled by Drude conductivity. We perform an analytical calculation in the framework of fluctuational electrodynamics where the additive contributions to the heat transfer by waves of different type separate naturally. This study allows us to evaluate the importance of retardation in the electromagnetic interaction according to the temperature, separation, and the material dc conductivity. Focusing on the Coulomb limit valid for poor metals at small separations, we use a richer model for the material response to investigate the roles and interplay of disorder, spatial dispersion, and collective charge density excitations called surface plasmons. From our analytical expressions we show that in a parametric window of separation and temperature scales the radiative heat current is indeed dominated by surface plasmons.

We go on to study the fluctuations, or noise, of the radiative heat current about its average value. We approach this much less well-understood quantity because it is expected to contain more physical information about the systems exchanging heat. In particular, we are interested in systems where the dominant contribution to the heat transfer comes collective or resonant excitations, where the heat current noise may provide an experimental probe of these excitations. We study analytically two such systems: an effective zero-dimensional system where the heat current is mediated by a superconducting resonator, and the familiar system of two-dimensional metallic layers whose heat transfer may be dominated by surface plasmons. In both cases the finite-frequency noise spectrum reveals a signature of the resonant transfer channel, that could potentially be measurable and hence provide a probe of the relevant excitations.


Supervisors : 
Denis BASKO, Laboratoire de Physique et de Modélisation des Milieux Condensés, PhD supervisor
Wolfgang BELZIG, University of Konstanz, PhD co-supervisor

Jury’s Members :
Jean-Jacques GREFFET, Laboratoire Charles Fabry, Institute d’Optique (CNRS / Université Paris- Saclay), Referee

Jukka PEKOLA, Aalto University, Referee
Gianluigi CATELANI, Forschungszentrum Jülich, Examiner
Hervé COURTOIS, Institut Néel (CNRS / Université Grenoble Alpes), Examiner
Bart VAN TIGGELEN, Laboratoire de Physique et de Modélisation des Milieux Condensés, Examiner