Open Access Nano Express

Electronic transmittance phase extracted from mesoscopic interferometers

M Ţolea1*, V Moldoveanu1, IV Dinu1 and B Tanatar2

Author Affiliations

1 , National Institute of Materials Physics, P. O. Box MG-7, Bucharest-Magurele 77125, Romania

2 Department of Physics, Bilkent University, Bilkent, Ankara 06800, Turkey

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Nanoscale Research Letters 2012, 7:568  doi:10.1186/1556-276X-7-568

Published: 13 October 2012

Abstract

The usual experimental set-up for measuring the wave function phase shift of electrons tunneling through a quantum dot (QD) embedded in a ring (i.e., the transmittance phase) is the so-called ‘open’ interferometer as first proposed by Schuster et al. in 1997, in which the electrons back-scattered at source and the drain contacts are absorbed by additional leads in order to exclude multiple interference. While in this case one can conveniently use a simple two-path interference formula to extract the QD transmittance phase, the open interferometer has also a number of draw-backs, such as a reduced signal and some uncertainty regarding the effects of the extra leads. Here we present a meaningful theoretical study of the QD transmittance phase in ‘closed’ interferometers (i.e., connected only to source and drain leads). By putting together data from existing literature and giving some new proofs, we show both analytically and by numerical simulations that the existence of phase lapses between consecutive resonances of the ‘bare’ QD is related to the signs of the corresponding Fano parameters - of the QD + ring system. More precisely, if the Fano parameters have the same sign, the transmittance phase of the QD exhibits a Π lapse. Therefore, closed mesoscopic interferometers can be used to address the ‘universal phase lapse’ problem. Moreover, the data from already existing Fano interference experiments from Kobayashi et al. in 2003 can be used to infer the phase lapses.

Keywords:
Phase measurement; Aharonov-Bohm interferometers; Phase lapse problem