7160

6666

كارشناسي ارشد

ماده چگال

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1390

ده، 76ص.: مصور، جدول، نمودار

ص.ع. به فارسي و انگليسي

فرهاد فضيله

علي اكبر بابايي بروجني

6/8/91

فرهاد شهبازي، پيمان صاحب سرا

1396/09/20

كتابنامه

فيزيك

فيزيك

ID6666

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Numerical Study of the Effect of Disorder and Magnetic Field on the QuantumTransport of two Dimensional Nanostructures Modeled in Tight binding Approximation Esmaeil Taghizadeh Sisakht etsisakht @yahoo com November Department of physics Isfahan University of Technology Isfahan Iran Degree M Sc language FarsiSupervisor Farhad Fazileh Mail fazileh@cc iut ac irAbstractIn recent years semiconductor nanostructures have become the model systems of choice for investigationsof electrical conduction on short length scales Quantum transport is conveniently studied in a twodimensional electron gas because of the combination of a large Fermi wavelength and large mean free path The phase coherence of charge carriers gives rise to the unique transport properties of mesoscopic systems Thismakes them interesting to study from a fundamental point of view but also gives these small systems a possiblefuture in nanoelectronics applications In the present work a numerical method is implemented in order tocontribute to the understanding of quantum transport in narrow channels that electrons have confined by anelectrostatic potential and therefore form a quasi one dimensional system we introduce an approach that hasproved to be very useful in describing mesoscopic transport In this approach the current through aconductor is expressed in terms of the probability that an electron can transmit through it Then we describeB ttiker extension on this approach to describe multi terminal measurement in magnetic fields generallyreferred to as the Landauer B ttiker formalism To simplify the discussion we assume zero temperature andphase coherent transport We introduce the concept of Green s functions and then show that a conductorconnected to infinite leads can be replaced by a finite conductor with the effect of the leads incorporatedthrough a self energy function This provides a convenient method for evaluating the Green s function andhence the transmission function numerically A numerical technique for calculating the transmissioncoefficients through a coherent mesoscopic conductor using it s green s function is introduced Theconductance of phase coherent quasi one dimensional systems is studied in ballistic diffusive and highfield regimes Our calculations was done in a model system with Hard wall boundary conditions in thetransverse direction and the Anderson model of disorder was used in disordered samples Spin splitting wasignored and spin degeneracy was assumed We have presented the results of quantum transport for differentstrengths of disorder and introduced magnetic fields Our results confirmed the Landauer formalism forcalculation of electronic transport We observed conductance fluctuations due to quantum interferencein our numerical results and showed that weak localization effect can be remove by application of aweak perpendicular magnetic field Magnetic depopulation of subbands in ballistic samples was studiednumerically Finally we showed numerically the transition to the integral quantum Hall effect regimethrough the suppression of backscattering on a disordere d model system by calculating the two terminal conductance of a quasi one dimensional quantum conductor as a s t r o n g magnetic field isapplied Our results showed that this regime is entered when there is negligible overlap between electron edgestates localized at opposite sides of the sample Key words quantum transport Green s function tight binding model disorder magnetotransport

فرهاد فضيله

علي اكبر بابايي بروجني

فرهاد شهبازي، پيمان صاحب سرا