Nonlinear Thermal Effects in Ballistic Electron Devices
Final rept. 1 Oct 2011-30 Sep 2012
LUND UNIV (SWEDEN) DEPT OF SOLID STATE PHYSICS
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Our results have shown that the transverse thermopower of the four-terminal junction with a central scatterer is very sensitive to the symmetry of the four QPC transmissions functions. We have shown that as a first order conceptual model, the four-terminal junction can be thought of as two pairs of QPCs, one left and one right. This model is capable of describing both the observed sign change in the transverse thermopower upon reversal of the thermal gradient, as well as the observed nonlinear effects in the transverse thermopowers. To fully take all four terminals into account, we have put forth a multi-terminal thermoelectric scattering theory, which we have used to extract the applied temperature increase as well as the effective transverse thermopower. Finally, we have experimentally demonstrated the fundamental magnetic-field symmetries of thermoelectric transport coefficients under thermal and electrical biases. We have also shown that these symmetries tend to decrease with increasing thermal bias. From our experiments we cannot conclude whether this symmetry breaking is due to a heating effect for example the destruction of phase coherence due to inelastic scattering or due to a nonlinear effect.
- Solid State Physics