Spin and valley control in carbon quantum dots

Nanostructures based on carbon have emerged as an interesting alternative material for spin qubits, due to both the low concentration of nuclear spins and relatively weak spin-orbit coupling. However, the formation of 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]. 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 sipn resonance (ESR). We describe this electron valley resonance (EVR) and its detection in a transport measurement [2]. 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 [3]. [1] B. Trauzettel, D. Bulaev, D. Loss, and G. Burkard, Nature Phys. 3, 192 (2007). [2] A. Pályi and G. Burkard, Phys. Rev. Lett. 106, 086801 (2011). [3] A. Pályi and G. Burkard, Phys. Rev. B 80, 201404 (2009); ibid. 82, 155424 (2010).

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