[f(k)] Colloquium Mika Prunnila today 10:15 FYS 1

[Ilari Maasilta]

Dear all,

welcome to today's physics colloquium,

Friday 18 March, at 10:15 in FYS1 Speaker:**Mika Prunnila, VTT***
Title:    ******Phonon tunneling and related near-field heat transfer 
effects*****

Abstract:

Non-contact heat transfer between distant objects is described by the 
well known black body radiation law. When the inter-body distance d is 
smaller than the characteristic wave length of Planck's spectrum 
near-field effects start to play crucial role in the inter-body heat 
transport and new physics emerges (see Refs. [1,2] for a review). Due to 
advances in experimental techniques various near-field heat transfer 
effects from micron down to nm body distances have been also verified 
experimentally.[3--5] A recent paper [6] proposes that at such distances 
a new type of near-field heat transfer mechanism due to acoustic phonons 
can exist. It should be noted that even though acoustic phonons are the 
major
heat carriers in dielectrics and semiconductors, their effect on 
non-contact heat transfer (through a vacuum gap) has been previously 
considered to be negligible, because they couple weakly to photons. 
However, significant energy transmission and heat flux is possible if 
the acoustic phonons can induce a time-dependent electric field, which 
then can leak into the vacuum.[6]  Suitable field-to-displacement 
coupling mechanism is provided, for example, by the piezoelectric 
effect. Solid-vacuum-solid acoustic phonon transmission can be thought 
of as an acoustic phonon tunneling through vacuum. In this presentation, 
we will discuss near-field heat
transfer effects and, especially, focus on the heat transfer due to 
phonon tunneling.
[1] K. Joulain et al., Surface Science Reports 57, 59 (2005).
[2] A. I. Volokitin and B. N. J. Persson, Rev. Mod. Phys. 79, 1291 (2007).
[3] A. Kittel et al., Phys. Rev. Lett. 95, 224301 (2005).
[4] A. Narayanaswamy, S. Shen, and G. Chen, Phys. Rev. B 78, 115303 (2008).
[5] E. Rousseau et al., Nature Photonics 3, 514 (2009).
[6] M. Prunnila and J. Meltaus, Phys. Rev. Lett. 105, 125501 (2010).




Best regards,

Kari Eskola and Ilari Maasilta

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