Tight-binding simulations of electrically driven spin-valley transitions   in carbon nanotube quantum dots
  We describe dynamics of spin and valley transitions driven by alternating electric fields in quantum dots defined electrostatically within semiconducting carbon nanotubes (CNT). We use the tight-binding approach to describe the states localized within a quantum dot taking into account the circumferential spin-orbit interaction due to the s-p hybridization and external fields. The basis of eigenstates localized in the quantum dot is used in the solution of the time-dependent Schroedinger equation for description of spin flips and inter-valley transitions that are driven by periodic perturbation in the presence of coupling between the spin, valley and orbital degrees of freedom. Besides the first order transitions we find also fractional resonances. We discuss the transition rates with selection rules that are lifted by atomic disorder and the bend of the tube. We demonstrate that the electric field component perpendicular to the axis of the CNT activates spin transitions which are otherwise absent and that the resonant spin-flip time scales with the inverse of the electric field. 
E. N. Osika, A. Mre\'nca, B. Szafran
cond-mat.mes-hall