Comment on 'Hysteresis, Switching, and Negative Differential Resistance in Molecular Junctions: a Polaron Model', by M. Galperin, M.A. Ratner, and A. Nitzan, Nano Lett. 5, 125 (2005)
Loading...
Date
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Description
It is shown that the ``hysteresis'' in a polaron model of electron transport through the molecule found by M.Galperin et al. [Nano Lett. 5, 125 (2005)] is an artefact of their ``mean-field'' approximation. The reason is trivial: after illegitimate replacement $\hat{n}^{2}=\hat{n}n_{0},$ where \hat{n} is the electron number operator, n_{0} the average molecular level occupation, Galperin et al. obtained non-physical dependence of a renormalized molecular energy level on the non-integer mean occupation number n_{0} (i.e. the electron self-interaction) and the resulting non-linearity of current. The exact theory of correlated polaronic transport through molecular quantum dots (MQDs) that we proposed earlier [Phys. Rev. B67, 235312 (2003)] proved that there is no hysteresis or switching in current-voltage characteristics of non-degenerate, d=1, or double degenerate, d=2, molecular bridges, contrary to the mean-field result. Switching could only appear in multiply degenerate MQDs with d>2 due to electron correlations. Most of the molecular quantum dots are in the regime of weak coupling to the electrodes addressed in our formalism.
3 pages, no figures; (v3) estimates added showing that most of the molecules are very resistive, so the actual molecular quantum dots are in the regime we study, unlike very transparent `molecules' studied by Galperin et al and other authors. In the latter case the molecules are rather `transparent' and, obviously, no current hysteresis can exist
3 pages, no figures; (v3) estimates added showing that most of the molecules are very resistive, so the actual molecular quantum dots are in the regime we study, unlike very transparent `molecules' studied by Galperin et al and other authors. In the latter case the molecules are rather `transparent' and, obviously, no current hysteresis can exist