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SEMICONDUCTORS AND NANOSTRUCTURES 2009Two-dimensional weak localization in polycrystalline granular SnO 2 filmsThe phenomenon of quantum interference in disorderedconductors is well known and its effects on the electricalconductance are widely used to determine the inelasticscattering time of charge carriers, and thus, the mechanismsof inelastic scattering. Because of the prominenteffects of weak localization in 2D systems they became anobject of intensive studies. However, the reduced dimensionalityand the presence of disorder lead not only to enhancementof interference effects, but also to the necessityto take into account the electron-electron interaction. It appearedthat such characteristics as density of states, temperatureand magnetic field dependencies of electrical conductancecould be described only if one takes into accountthe effects of electron-electron interaction in a disorderedlow-dimensional system [Altshuler and Aronov, Modernproblems in condensed matter sciences Vol 10, Efros andPollak. ed., North Holland 1985]. Moreover, the dephasingmechanisms in weak localization are strongly relatedto interaction effects; inelastic electron-phonon scattering,quasi-elastic electron-electron scattering with small energytransfer. The interplay of interference and interaction effectsremains a puzzling problem that is still far from beingsolved.(2006)] where the weak localization model is extended beyondthe diffusion limit. In the frame of this model, onlysmall closed loops are believed to give contribution to theeffect of weak localization at such high magnetic fields, theminimum number of collisions in each loop being 3. Onecan suppose that relative to electron-electron interaction effects,these triangles should be easier to study rather thanany complicated electronic path with a large number of collision.As in many materials the dephasing in the weak localizationeffect was found to be due to electron-electroninteractions, the study of these materials in high magneticfields should provide important information about these interactions(single electron’s wave function interference isdestroyed, so the interaction effects should give the maincontribution to magnetoconductance).In our SnO 2 polycrystalline films the low transverse magneticfield dependence of the conductance is positive andcan be described in the frame of a 2D weak localizationmodel, the phase breaking mechanism being electronelectronscattering with small energy transfer.In figure 64, the dependence of the magnetoconductance onthe normalized magnetic field B/B ϕ , measured on the samesample, are presented over the full range of applied magneticfield up to 50 T. Here, B ϕ is the value of magnetic fieldat which the flux of magnetic field through an area enclosedby the electron’s paths becomes equal to the flux quantumh/2e. From both the inset, where the curves are presentedin linear coordinates, and from the main part of figure 64,one can see that at high fields the curves exhibit differentbehaviour and no longer overlap any more. We thus suggestthe necessity to take into account the anisotropy ofthe scattering potential in order to describe the observedresults. Different particularities of single scattering eventsmay have influence at different temperatures in this highfield region.The experimental curves in figure 64 resemble those derivedby Zduniak et al. [Phys. Rev. B 56, 1996 (1997)]and by Germanenko et al. [Phys. Rev. B 73, 233301Figure 64: The magnetic field dependencies of magnetoconductanceas a function of normalized magnetic field. Inset shows fielddependencies of magnetoresistance in linear coordinates measuredon the same sample.The analysis of high-field magnetoresistance data, obtainedon our samples of SnO 2 polycrystalline thin films, will provideanother one possibility to justify the mechanism ofelectron-electron interaction in disordered systems. The advantageof our samples is in highly controllable degree ofdisorder, which provides possibility to tune the range of occurrenceof quantum interference under applied magneticfields.T. A. Dauzhenka, J. GalibertV. K. Ksenevich (Belarus State University, Dept Phys. SC & Nanoelectronics, BY-Minsk), I.A. Bashmakov (BelarusState Univ. Research Institute of Physicochemical Problems, BY-Minsk)48