ELFT HÍRADÓ

[Szommer Peter <szpl AT metal.elte.hu>]

ELTE Fizikai Intézet

                               ORTVAY KOLLOKVIUM
                                
                    2012. április 26., csütörtök, 15 órakor
                Az ELTE Pázmány Péter s. 1/A alatti épületében
                           földszinti 0.81 előadóban


   Guido Burkard (Department of Physics, University of Konstanz, Germany):
          "Spin and valley control in graphene and carbon nanotubes"



Kivonatos ismertetés:

Carbon has emerged as an interesting material for coherent spin physics and 
spin qubits, due to both the low concentration of nuclear spins and relatively 
weak spin-orbit coupling. However, the localization of electrons in quantum 
dots in graphene is a non-trivial task due to the absence of a band gap and 
the related effect of Klein tunneling [1]. However, the vicinity of the 
valence band also offers interesting possibilities, e.g. for non-local spin 
coupling [2]. Interestingly, electrons in carbon-based quantum dots comprise 
a degree of freedom in addition to spin: The existence of two Dirac cones in 
the graphene band structure leads to the valley degree of freedom which can 
be coherently manipulated with oscillatory fields in a similar way as the 
spin in electron spin resonance (ESR). We describe this electron valley 
resonance (EVR) and its detection in a transport measurement [3]. The valley 
degeneracy also enters the hyperfine interactions with remaining 13C nuclear 
spins as well as non-magnetic atomic impurities and plays an important role 
in the spin-valley blockade effect in double quantum dots formed in a carbon 
nanotube [4].



[1] B. Trauzettel, D. Bulaev, D. Loss, and G. Burkard, Nature Phys. 3, 192 
(2007).

[2] M. Braun, P. R. Struck, and G. Burkard, Phys. Rev. B 84, 115445 (2011).

[3] A. Pályi and G. Burkard, Phys. Rev. Lett. 106, 086801 (2011).

[4] A. Pályi and G. Burkard, Phys. Rev. B 80, 201404 (2009); ibid. 82, 155424 (2010).