Vinitha Balachandran, Riccardo Bosisio, Giuliano Benenti
We report our investigations on the finite size effects of Lorenz number in a
molecular wire. Using Landauer-B\"uttiker formalism, we find that for
sufficiently long wires there are two validity regimes of Wiedemann-Franz (WF)
law, the cotunneling and the sequential tunneling regimes, while in small
systems only the first regime survives. We compare our results with standard
Kubo formalism and explain its failure to detect the WF law in small systems.
Furthermore, our studies on exponentially localized disordered wires show that
Lorenz number value L_0 predicted by WF law is obtained only in the cotunneling
regime. Also, Lorenz number L exhibits typical distribution at different
temperatures corresponding to different tunneling process. In particular, first
order tunneling results in a low value of L whereas second order tunneling
recovers the universal value L_0.
View original:
http://arxiv.org/abs/1202.5109
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