Voltage controlled spin precession in InAs quantum wells

In this work we investigate spin diffusion in InAs quantum wells with the Rashba spin-orbit coupling modulated by a gate voltage. The gate voltage dependence of the spin diffusion under different temperatures is studied with all the scattering explicitly included. Our result partially supports the claim of the realization of the Datta-Das spin-injected field effect transistor by Koo {\it et al.} [Science {\bf 325}, 1515 (2009)]. We also show that the scattering plays an important role in spin diffusion in such a system.Comment: 4 pages, 2 figure

Substrate effects on quasiparticles and excitons in graphene nanoflakes

The effects of substrate on electronic and optical properties of triangular and hexagonal graphene nanoflakes with armchair edges are investigated by using a configuration interaction approach beyond double excitation scheme. The quasiparticle correction to the energy gap and exciton binding energy are found to be dominated by the long-range Coulomb interactions and exhibit similar dependence on the dielectric constant of the substrate, which leads to a cancellation of their contributions to the optical gap. As a result, the optical gaps are shown to be insensitive to the dielectric environment and unexpectedly close to the single-particle gaps.Comment: 4 pages, 4 figure