Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 26: Transport: Graphene and Carbon Nanotubes

TT 26.2: Talk

Wednesday, March 25, 2009, 14:30–14:45, HSZ 03

Quantum spin Hall state in gapless graphene? — •Martina Hentschel and Grigory Tkachov — MPI für Physik komplexer Systeme, Dresden

We demonstrate the possibility of a quantum spin Hall state in a two-dimensional gas of massless Dirac fermions as is realized in graphene [1]. To this end we use a generalized zigzag-confinement model that admits a spin-orbit interaction. At a certain critical strength the spin-orbit coupling induces a phase transition of the quantum-spin-Hall type. It is characterized by the existence of a novel type of edge states consisting of a Kramers pair of counter propagating modes with opposite spin orientations (i.e. exhibiting spontaneous quantum Hall effects of opposite signs). These edge states are capable of accumulating an integer spin. They exist without any excitation gap in the bulk, due to which our system stands out among other quantum spin Hall systems studied earlier [2-4]. We show that the local density of states is discontinuous at the transition and its energy dependence reflects the phase diagram of the system.

[1] G. Tkachov and M. Hentschel, arXiv: 0803.0713.

[2] C. L. Kane and E. J. Mele, Phys. Rev. Lett. 95, 226801 (2005).

[3] B. A. Bernevig and S. C. Zhang,

Phys. Rev. Lett. 96, 106802 (2006).

[4] M. König, S. Wiedmann, C. Brüne, A. Roth, H. Buhmann,

L. W. Molenkamp, X.-L. Qi, and S.-C. Zhang

Science 318, 766-770 (2007).