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21.01.2010. :: SCL seminar

 

Laboratorija za primenu racunara u nauci najavljuje seminar

"Graphene under uni-axial strain and 2D layered organic material alpha-(BEDT-TTF)_2I_3 – the physics of tilted Dirac cones"

Mark Oliver Goerbig
Laboratoire de Physique des Solides, CNRS, Université Paris-Sud

koji ce se odrzati u cetvrtak, 21. januara 2010. godine u biblioteci Instituta za fiziku sa pocetkom u 12 casova.


Apstrakt:

Dirac-fermion physics in condensed-matter physics has become a major issue since the discovery of graphene – a one-atom thick layer of graphite – where the low-energy electronic properties are governed by the relativistic Dirac rather than a Schrödinger equation. It has recently been argued that Dirac fermions would also be responsible for the particular electronic properties in the layered organic material alpha-(BEDT-TTF)_2I_3 [1], the temperature-dependent transport of which hints at a narrow (or even zero) semiconductor under pressure [2].

An interesting difference as compared to graphene arises from the tilt of the (anisotropic) Dirac cones in alpha-(BEDT-TTF)_2I_3, which has been obtained in a tight-binding calculation [1]. In this talk, I discuss the origins of this tilt as well as its consequence for the Landau-level quantisation in a strong magnetic field [3]. Surprisingly, the effect of the tilt yields the same modification of the Landau levels as an in-plane electric field for the case of non-tilted cones, which lowers indeed the Landau-level spacing as a consequence of an underlying Lorentz invariance [4]. Whereas neither the tilt of the Dirac cones nor the in-plane electric field may lift, on their own, the twofold valley degeneracy in these systems, the combination of the two achieves such as degeneracy lifting [5]. This scenario may eventually be tested with the help of infrared spectroscopy that has proven to be a powerful tool in the determination of the particular relativistic Landau-level structure in graphene.

[1] S. Katayama, A. Kobayashi, and Y. Suzumura, J. Phys. Soc. Jpn. 75, 054705 (2006).
[2] N. Tajima, S. Sugawara, M. Tamura, Y. Nishio, and K. Kajita, J. Phys. Soc. Jpn. 75, 051010 (2006).
[3] M. O. Goerbig, J.-N. Fuchs, G. Montambaux, and F. Piéchon, Phys. Rev. B 78, 045415 (2008).
[4] V. Lukose, R. Shankar, and G. Baskaran, Phys. Rev. Lett. 98, 116802 (2007).
[5] M. O. Goerbig, J.-N. Fuchs, G. Montambaux, and F. Piéchon, EPL 85, 57005 (2009).


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