Quantum spin Hall effect in graphene nanoribbons: Effect of edge eometry
* SPEAKERS
Name
Affiliation
E-mail
Jun-Won Rhim
KIAS
* HOST(Applicant)
Name
Affiliation
E-mail
Gun Sang Jeon
Ewha Womans Univ.
gsjeon(at)ewha.ac.kr
* DATE / TIME
2011-11-04, 3:00 p.m.
* PLACE
ECC B155, Ewha Womans Univ., Seoul, Korea
* ABSTRACT
There has been tremendous recent progress in realizing topological insulator initiated by the proposal of Kane and Mele for the graphene system. They have suggested that the odd Z2 index for the graphene manifests the spin-filtered edge states for the graphene nanoribbons, which lead to the quantum spin Hall effect (QSHE). Here, we investigate the role of the spin-orbit interaction both for the zigzag and armchair nanoribbons with special care in the edge geometry. For the pristine zigzag nanoribbons, we have shown that one of the σ edge bands located near E = 0 lifts up the energy of the spin-filtered chiral edge states at the zone boundary by warping the π edge bands, and hence the QSHE does not occur. Upon increasing the carrier density above a certain critical value, the spin-filtered edge states are formed leading to the QSHE. We suggest that the hydrogen passivation on the edge can recover the original feature of the QSHE. For the armchair nanoribbon, the QSHE is shown to be stable. We have also derived the real-space effective Hamiltonian, which demonstrates that the on-site energy and the effective spin-orbit coupling strength are strongly enhanced near the ribbon edges. We have shown that the steep rise of the confinement potential thus obtained is responsible for the warping of the π edge bands.
