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Electronic and Spin Transport in Dirac-Like Systems

Asmar, Mahmoud M.

Abstract Details

2015, Doctor of Philosophy (PhD), Ohio University, Physics and Astronomy (Arts and Sciences).
In this dissertation we study transport properties of graphene within the low energy Dirac approximation. We utilize partial wave scattering methods and relate the scattering matrix elements to physical observables such as the elastic time, transport time, and skewness of scattering. We suggest that experimentally measurable quantities, such as the transport to elastic time ratio, indicate the presence of perturbations that lead to the reduction of symmetries of graphene, as well as spin-orbit interactions. This result relies on the fact that perturbations that leave graphene symmetries untouched, such as potential scatterers, display a constant ratio of transport to elastic times at low energies, making this ratio robust to random scatterer size and strength disorder. We also show that this ratio is not robust to either symmetry breaking perturbations or spin-orbit interactions, as these interactions lead to the ratio deviating from its ideal value. Even though both kinds of perturbations, symmetry breaking and spin-orbit interactions, lead to changes in the ratio, we show that the qualitatively different dependence on energy for each of these perturbations allows the experimental identification and quantification of both effects simultaneously. We have also shown, in relation to the spin Hall effect detection in graphene, that even though the local enhancement of spin-orbit interactions leads to the appearance of a spin Hall effect signal robust to potential and size disorder, the breaking of effective time reversal symmetry through local perturbations leads to the appearance of a valley Hall effect through skew scattering. This valley skew processes contribute to the non-local resistance that helps quantify the Hall effect. Similarly, we show that multiple potential scatterers with space dependence that breaks parity in graphene, also lead to the appearance of a valley Hall effect due to the separation of electrons from different valleys in space through skew scattering. These results suggest that measured spin Hall effect in graphene is not robust to the latter perturbations, indicating that this effect may not be completely produced by local enhancement of spin orbit interactions alone, but as suggested before, may be accompanied by a competing valley Hall effect that overestimates the measured effect. Finally, in the high energy regime we show that long-lived quasi-bound states in graphene gated regions mimic the behavior of whispering gallery modes. In the limit of electron optics, we have also shown how gated regions in graphene are analogous to lenses with variable index of refraction, and that the presence of spin-orbit interactions makes these lenses birefringent, with a degree of birefringence that indicates the strength of the spin-orbit enhancement.
Ulloa Sergio E., PhD (Advisor)
165 p.

Recommended Citations

Citations

  • Asmar, M. M. (2015). Electronic and Spin Transport in Dirac-Like Systems [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1437564830

    APA Style (7th edition)

  • Asmar, Mahmoud . Electronic and Spin Transport in Dirac-Like Systems. 2015. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1437564830.

    MLA Style (8th edition)

  • Asmar, Mahmoud . "Electronic and Spin Transport in Dirac-Like Systems." Doctoral dissertation, Ohio University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1437564830

    Chicago Manual of Style (17th edition)