Abstract
Quantum effects are expected to disappear in the short-wavelength, semiclassical limit. As a matter of fact, recent investigations of transport through quantum chaotic systems have demonstrated the exponential suppression of the weak localization corrections to the conductance and of the Fano factor for shot noise when the Ehrenfest time ${\ensuremath{\tau}}_{E}$ exceeds the electronic dwell time ${\ensuremath{\tau}}_{D}$. On the other hand, conductance fluctuations, an effect of quantum coherence, retain their universal value in the limit ${\ensuremath{\tau}}_{E}/{\ensuremath{\tau}}_{D}\ensuremath{\rightarrow}\ensuremath{\infty}$, when the system is ideally coupled to external leads. Motivated by this intriguing result we investigate conductance fluctuations through quantum chaotic cavities coupled to external leads via (tunnel) barriers of arbitrary transparency $\ensuremath{\Gamma}$. Using the trajectory-based semiclassical theory of transport, we find that the linear ${\ensuremath{\tau}}_{E}$ dependence of the conductance variance shows a nonmonotonous, sinusoidal behavior as a function of $\ensuremath{\Gamma}$. Most notably, we find an increase of the conductance fluctuations with ${\ensuremath{\tau}}_{E}$, above their universal value, for $\ensuremath{\Gamma}\ensuremath{\lesssim}0.5$. These results, confirmed by numerical simulations, show that, contrary to common wisdom, effects of quantum coherence may increase in the semiclassical limit, under special circumstances.
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