We investigate the effects of homogeneous and inhomogeneous deformations and edge disorder on the conductance of gated graphene nanoribbons. Under increasing homogeneous strain the conductance of such devices initially decreases before it acquires a
resonance structure, and finally becomes completely suppressed at larger strain. Edge disorder induces mode mixing in the contact regions, which can restore the conductance to its ballistic value. The valley-antisymmetric pseudo-magnetic field induced by inhomogeneous deformations leads to the formation of additional resonance states, which either originate from the coupling into Fabry-Perot states that extend through the system, or from the formation of states that are localized near the contacts, where the pseudo-magnetic field is largest. In particular, the n=0 pseudo-Landau level manifests itself via two groups of conductance resonances close to the charge neutrality point.
We describe the weak localization correction to conductivity in ultra-thin graphene films, taking into account disorder scattering and the influence of trigonal warping of the Fermi surface. A possible manifestation of the chiral nature of electrons
in the localization properties is hampered by trigonal warping, resulting in a suppression of the weak anti-localization effect in monolayer graphene and of weak localization in bilayer graphene. Intervalley scattering due to atomically sharp scatterers in a realistic graphene sheet or by edges in a narrow wire tends to restore weak localization resulting in negative magnetoresistance in both materials.
We model the optical visibility of monolayer and bilayer graphene deposited on a silicon/silicon oxide substrate or thermally annealed on the surface of silicon carbide. We consider reflection and transmission setups, and find that visibility is stro
ngest in reflection reaching the optimum conditions when the bare substrate transmits light resonantly. In the optical range of frequencies a bilayer is approximately twice as visible as a monolayer thereby making the two types of graphene distinguishable from each other.
We propose a kinetic theory to describe the power dependence, $I_{PC}(P)$, of the photocurrent (PC) lineshape in optically pumped quantum dots at low temperatures, in both zero and finite magnetic fields. We show that there is a crossover power $P_c$
, determined by the electron and hole tunneling rates, at which the photocurrent spectra become strongly influenced by the dot kinetics, and no longer reflect the exciton lifetime in the dot. For $P>P_c$, we show that the photocurrent saturates due to the slow hole escape rate (in e.g., InGaAs/GaAs dots), whereas the line-width increases with power: $Gamma propto sqrt{P}$. We also analyze to what measure the spin-doublet lineshape of the photocurrent studied in a high magnetic field reflects the degree of circular polarization of the incident light.
We demonstrate that bistability of the nuclear spin polarization in optically pumped semiconductor quantum dots is a general phenomenon possible in dots with a wide range of parameters. In experiment, this bistability manifests itself via the hystere
sis behavior of the electron Zeeman splitting as a function of either pump power or external magnetic field. In addition, our theory predicts that the nuclear polarization can strongly influence the charge dynamics in the dot leading to bistability in the average dot charge.
