Az ELTE Nanofizika Szeminárium jövő hétfői dupla előadása:
(Kezdés 10:05-kor, 10 perccel a szokott 10:15 előtt!)

10:05-11:00
Sári Judit (PTE): Inter-Landau-level magnetoexcitons in bilayer graphene

11:05-12:00
Makk Péter (Basel): MoS2 for valleytronics

Helyszin: ELTE Eszaki Tömb, 5.55-os terem (1117 Budapest, Pázmány Péter sétany 1/A)
Időpont: 2013. május 6., hétfő, 10:05

Minden érdeklődőt szívesen látunk.

A szeminárium további programja: http://wigner.elte.hu/koltai/science/?q=seminar

Sári Judit (PTE): Inter-Landau-level magnetoexcitons in bilayer graphene

The last decade has witnessed an immense growth of interest in two-dimensional materials after the experimental confirmation of the existence of graphene, a monolayer graphite allotrope in 2004 [1]. One of the most peculiar properties of graphene monolayers and multilayers is the unconventional quantum Hall effect characteristic to both monolayer and bilayer graphene [2].
In the case of bilayer graphene, several quantum Hall plateaux are observed at low enough temperatures. Of these, the ?xy = 4ne2/h sequence (n _= 0) is explained by standard Landau quantization, while the other integer plateaux arise due to interactions. The low-energy excitations in both cases are magnetoexcitons, whose dispersion relation depends on single- and many-body effects in a complicated manner [3]. In the first part of the lecture a short introduction will be given to the Landau level structure of bilayer graphene, afterwards the approach of magnetoexcitons is summarized.
The second part of the lecture describes the result of our analysis of the magnetoexciton modes in bilayer graphene [4]. We find that the mixing of different Landau level transitions not only renormalizes them, but essentially changes their spectra and orbital character at finite wavelength. These predictions can be probed in inelastic light scattering experiments.
References:
[1] K. S. Novoselov et al., Nature 438, 197 (2005) and Y. Zhang et al., Nature 438, 201 (2005).
[2] K. S Novoselov et al., Nature Physics 2, 177 (2006).
[3] For the approach of magnetoexcitons, see C. Kallin and B. I. Halperin, PRB 30, 5655 (1984); I. V. Lerner and Yu. E. Lozovik, Zh. Eksp. Teor. Fiz. 78, 1167 (1980) [Sov. Phys. JETP 51, 588 (1981)]; Yu. A. Bychkov, S.
V. Iordanskii, and G. M. Eliashberg, Pis'ma Zh. Eksp. Teor. Fiz. 33, 152 (1981) [Sov. Phys. JETP Lett. 33, 143 (1981)]; Yu. A. Bychkov, E. I. Rashba, Zh. Eksp. Teor. Fiz. 85, 1826 (1980) [Sov. Phys. JETP 58, 1062 (1983)].
[4] J. Sári and Cs. Tőke, Phys. Rev B 87 085432 (2013).

Makk Péter (Basel): MoS2 for valleytronics

After the discovery of graphene several proposals have been put forward to use the valley degree of freedom for electronic devices. This concept is called valleytronics. However the realisation of these proposals for graphene is extremely challenging, mainly because of the valley scattering present in graphene. Recently, it was shown, that single layer MoS2 (molybdenum disulphide) can provide an alternative to graphene for valleytronics applications as a result of its special electronics properties. In my talk I will review some of the recent results in the literature on single layer MoS2 devices.