ELFT HÍRADÓ

[andraspalyi AT caesar.elte.hu]

Az ELTE Nanofizika Szeminarium jovo hetfoi dupla eloadasa:
(Kezdes 10:05-kor, 10 perccel a szokott 10:15 elott!)


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 Tomb, 5.55-os terem (1117 Budapest, Pazmany  
Peter setany 1/A),
Idopont: 2013. majus 6., hetfo, 10:05


Minden erdeklodot szivesen latunk.

A szeminarium tovabbi programja:  
http://wigner.elte.hu/koltai/science/?q=seminar

Udvozlettel,
Palyi Andras

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Ui.: Az eloadasok absztraktjai:

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).


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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.