Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...
Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...
Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...
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Posters Monday February 4<br />
Poster 15:<br />
Mechanism for Giant Thermopower in Negative-U Molecular Quantum Dots<br />
Theo Costi<br />
We investigate with the aid of numerical renormalization group techniques<br />
the thermoelectric properties of a molecular quantum dot described by the<br />
negative-U An<strong>der</strong>son model. We show that the charge Kondo effect provides<br />
a mechanism for enhanced thermoelectric power via a correlation-induced<br />
asymmetry in the spectral function close to the Fermi level. We show that<br />
this effect results in a dramatic enhancement of the Kondo-induced peak in<br />
the thermopower of negative-U systems with Seebeck coefficients exceeding<br />
50 µV/K over a wide range of gate voltages [1,2].<br />
[1] S. An<strong>der</strong>gassen, T. A. Costi and V. Zlatic, Phys. Rev. B 84, 241107 (R)<br />
(2011)<br />
[2] T. A. Costi and V. Zlatic, Phys. Rev. Lett. {bf 108}, 36402 (2012); in<br />
"New Materials for Thermoelectric Applications: Theory and Experiment",<br />
ed. V. Zlatic and A. C. Hewson, ISBN 978-94-007-4983-2 (Springer, Berlin,<br />
2012)<br />
Coauthors: S. An<strong>der</strong>gassen and V. Zlatic<br />
Poster 16:<br />
Boltzmann-type approach to thermal drag in spin-1/2-lad<strong>der</strong> systems coupled<br />
to phonons<br />
Christian Bartsch<br />
We quantitatively investigate the spin-phonon drag contributions to the<br />
thermal conductivity of a two-leg-spin-1/2-lad<strong>der</strong> coupled to lattice vibrations<br />
in a magnetoelastic way. By applying suitable transformations the<br />
system is mapped onto a weakly interacting quantum gas model of bosonic<br />
spin excitations (magnons) and phonons. We adequately construct a collision<br />
term of a linear(ized) Boltzmann equation from the un<strong>der</strong>lying quantum<br />
dynamics by means of a pertinent projection operator technique. From the<br />
Boltzmann equation we obtain concrete numerical values for the drag conductivity<br />
and relate it to the individual thermal conductivities of magnons and<br />
phonons for parameter ranges which are typical for certain material classes.<br />
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