Ballistic transport properties across nonuniform strain barriers in graphene

We study the effect of uniaxial strain on the transmission and the conductivity across a strain-induced barrier in graphene. At variance with conventional studies, which consider sharp barriers, we consider a more realistic, smooth barrier, characterized by a nonuniform, continuous strain profile. Our results are instrumental towards a better understanding of the transport properties in corrugated graphene.Comment: High Press. Res., to appea

Pairing symmetry of superconducting graphene

The possibility of intrinsic superconductivity in alkali-coated graphene monolayers has been recently suggested theoretically. Here, we derive the possible pairing symmetries of a carbon honeycomb lattice and discuss their phase diagram. We also evaluate the superconducting local density of states (LDOS) around an isolated impurity. This is directly related to scanning tunneling microscopy experiments, and may evidence the occurrence of unconventional superconductivity in graphene.Comment: Eur. Phys. J. B, to appea

Extended d

Remarkable anisotropic structures have been recently observed in the order parameter $\Delta_{\bf k}$ of the underdoped superconductor Bi2Sr2CaCu2O$_{8+\delta}$. Such findings are strongly suggestive of deviations from a simple $d_{x^2 - y^2}$-wave picture of high-Tc superconductivity, i.e. $\Delta_{\bf k}\sim \cos k_x - \cos k_y$. In particular, flatter nodes in $\Delta_{\bf k}$ are observed along the $k_x = \pm k_y$ directions in ${\bf k}$-space, than within this simple model for a d-wave gap. We argue that nonlinear corrections in the ${\bf k}$-dependence of $\Delta_{\bf k}$ near the nodes introduce new energy scales, which would lead to deviations in the predicted power-law asymptotic behaviour of several measurable quantities, at low or intermediate temperatures. We evaluate such deviations, either analytically or numerically, within the interlayer pair-tunneling model, and within yet another phenomenological model for a d-wave order parameter. We find that such deviations are expected to be of different sign in the two cases. Moreover, the doping dependence of the flatness of the gap near the nodes is also attributable to Fermi surface effects, in addition to possible screening effects modifying the in-plane pairing kernel, as recently proposed