We study the effect of disordered ripples on the conductivity of monolayer graphene flakes. We calculate the relaxation times and the Boltzmann conductivities associated with two mechanisms. First, we study the conductivity correction due to an external in-plane magnetic field B . Due to the irregular local curvature found at graphene sheets deposited over a substrate, B can be mapped into an effective random magnetic field perpendicular to the graphene surface. Second, we study the electron momentum relaxation due to intrinsic pseudo magnetic fields originated from deformations and strain. We find that the competition between these mechanisms gives rise to a strong anisotropy in the conductivity tensor. This result provides a new strategy to quantitatively infer the strength of pseudo-magnetic fields in rippled graphene flakes.
Spin torques at topological insulator (TI)/ferromagnet interfaces have received considerable attention in recent years with a view towards achieving full electrical manipulation of magnetic degrees of freedom. The most important...
The relative contributions of bulk and surface states to the spin torque at topological insulator (TI)/ferromagnet interfaces are poorly understood. Here we study spin torques due to TI bulk states and show that: (i) There is no spin torque on a homogeneous magnetization; (ii) There is a spin transfer torque on an inhomogeneous magnetization, which is small in our idealized model but may be sizable in real samples; (iii) There is no bulk spin-Hall effect. A smoking gun for experiment is the comparable size of the spin transfer torque for in-plane and out-of-plane magnetizations.
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