Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 19: Symposium Spin-Orbit Coupling and Spin Relaxation in Graphene and Carbon Nanotubes

O 19.5: Invited Talk

Monday, March 22, 2010, 16:35–17:10, H1

Spin relaxation and decoherence in graphene quantum dots — •Guido Burkard — Dept. of Physics, Univ. of Konstanz, Germany

Graphene is a promising material for electron spin qubits due to its low concentration of nuclear spins and relatively weak spin-orbit coupling [1]. Despite the expected weakness of spin relaxation and decoherence effects, the time scales for these processes are relevant for coherent spin manipulations in graphene. We have calculated the spin relaxation time T₁ of a single spin in graphene quantum dots [1,2] as a function of the magnetic field B. In quantum dots without coupling between the valleys K and K′ in the graphene band structure, there is an effective time-reversal symmetry breaking which prevents the Van Fleck cancellation at B=0 known from semiconductor quantum dots. This leads to a distinct value of the exponent α in the power law T₁ ∝ B^α which can be different from the value for semiconductor quantum dots. In the context of spin decoherence, we have also studied the form of the hyperfine interaction with ¹³C atoms in graphene and find that it leads to a spin-valley coupling [3]. In the transport current through a double quantum dot, we find that the valley degeneracy and hyperfine-induced spin-valley coupling in graphene lead to features in the Pauli blockade that are qualitatively different from the known effect for semiconductor quantum dots.

[1] B. Trauzettel, D.V. Bulaev, D. Loss, and G. Burkard, Nature Phys. 3, 192 (2007). [2] P. Recher, J. Nilsson, G. Burkard, and B. Trauzettel, Phys. Rev. B 79, 085407 (2009). [3] A. Palyi and G. Burkard, Phys. Rev. B 80, 201404(R) (2009).