[institut] Seminar Mark Goerbig

[Milica Milovanovic]

Postovane kolege,

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

odrzace seminar:

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

u cetvrtak, 21.01.2010., u 12.00 u sali biblioteke Instituta za fiziku.

Sazetak seminara:

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).






Milica V. Milovanovic
-----------------
Institute of Physics Belgrade
http://www.ipb.ac.rs/