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Title: Magnetoresistance and Dephasing in a Two-dimensional Electron Gas at Intermediate Conductances
Authors: Minkov, G. M.
Germanenko, A. V.
Gornyi, I. V.
Issue Date: 2004
Publisher: American Physical Society
American Physical Society (APS)
Citation: Minkov G. M. Magnetoresistance and Dephasing in a Two-dimensional Electron Gas at Intermediate Conductances / G. M. Minkov, A. V. Germanenko, I. V. Gornyi // Physical Review B - Condensed Matter and Materials Physics. — 2004. — Vol. 70. — Iss. 24. — P. 1-24. — 245423.
Abstract: We study, both theoretically and experimentally, the negative magnetoresistance (MR) of a two-dimensional (2D) electron gas in a weak transverse magnetic field B. The analysis is carried out in a wide range of zero-B conductances g (measured in units of e2/h), including the range of intermediate conductances g∼1. Interpretation of the experimental results obtained for a 2D electron gas in GaAs/InxGa 1-xAs/GaAs single quantum well structures is based on a theory that takes into account terms of higher orders in 1/g. We show that the standard weak localization (WL) theory is adequate for g ≳ 5. Calculating the corrections of second order in 1/g to the MR, stemming from both the interference contribution and the mutual effect of WL and Coulomb interaction, we expand the range of a quantitative agreement between the theory and experiment down to significantly lower conductances g∼1. We demonstrate that at intermediate conductances the negative MR is described by the standard WL "digamma-functions" expression, but with a reduced prefactor α. We also show that at not very high g the second-loop corrections dominate over the contribution of the interaction in the Cooper channel, and therefore appear to be the main source of the lowering of the prefactor α≃1-2/πg. The fitting of the MR allows us to measure the true value of the phase breaking time within a wide conductance range g≳1. We further analyze the regime of a "weak insulator," when the zero-B conductance is low g(B=0)<1 due to the localization at low temperature, whereas the Drude conductance is high g0≫1, so that a weak magnetic field delocalizes electronic states. In this regime, while the MR still can be fitted by the digamma-functions formula, the experimentally obtained value of the dephasing rate has nothing to do with the true one. The corresponding fitting parameter in the low-T limit is determined by the localization length and may therefore saturate at T→0, even though the true dephasing rate vanishes. © 2004 The American Physical Society.
Keywords: ARTICLE
Access: info:eu-repo/semantics/openAccess
SCOPUS ID: 14944380372
PURE ID: 8532682
ISSN: 1098-0121
metadata.dc.description.sponsorship: We are grateful to I. L. Aleiner, A. D. Mirlin, D. G. Polyakov, P. Wölfle, and A. G. Yashenkin for interesting discussions and valuable comments. We thank O. I. Khrykin, V. I. Shashkin, and B. N. Zvonkov for growing the samples. This work was supported by the RFBR through Grants No. 02-02-17688, No. 03-02-16150, and No. 04-02-16626, the Program Russian Science School 2192.2003.2, the INTAS through Grant No. 1B290, the CRDF through Grants No. EK-005-X1 and No. Y1-P-05-11, the Russian Program “Physics of Solid State Nanostructures,” the Program of Russian Academy of Science, the Schwerpunktprogramm “Quanten-Hall-Systeme,” and the SFB195 der Deutschen Forschungsgemeinschaft.
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