William J. Herrera

Microscopic theory of Cooper pair beam splitters based on carbon nanotubes

This work was supported by MICINN-Spain via Grant No. FIS2008-04209, the EU FP7 project SE2ND (P.B. and A.L.Y.), and DIB from Universidad Nacional de Colombia, Project No. 12170 (W.J.H.)

A Green function approach to graphene–superconductor junctions with well-defined edges

This work presents a novel approach to describing spectral properties of graphene layers with well-defined edges. We microscopically analyze the boundary problem for the continuous Bogoliubov-de Gennes-Dirac equations and derive the Green functions for normal and superconducting graphene layers. Importing the idea used in tight-binding models of a microscopic hopping that couples different regions, we are able to set up and solve an algebraic Dyson equation describing a graphene-superconductor junction. For this coupled system we analytically derive the Green functions and use them to calculate the local density of states and the spatial variation of the induced pairing correlations in the normal region. Signatures of specular Andreev reflections are identified.

Selective focusing of electrons and holes in a graphene-based superconducting lens

This work was supported by COLCIENCIAS, project 110152128235 (S.G. and W.J.H.), and MICINN-Spain via Grant No. FIS2008-04209 and EU project SE2ND

Quantum point contact conductance in normal-metal/insulator/metal/superconductor junctions

The effect of an insulating barrier located at a distance

Long-range crossed Andreev reflections in high-temperature superconductors

a

Moments of inertia for solids of revolution and variational methods

from a NS quantum point contact is analyzed in this work. The Bogoliubov de Gennes equations are solved for NINS junctions (S: anysotropic superconductor, I: insulator and N: normal metal), where the NIN region is a quantum wire. For

Work and energy in inertial and noninertial reference frames

% a\neq0

The geometrical nature and some properties of the capacitance coefficients based on Laplace’s equation

, bound states and resonances in the differential conductance are predicted. These resonances depend on the symmetry of the pair potential, the strength of the insulating barrier and

Proximity-induced interface bound states in superconductor-graphene junctions

a

Electrostatic internal energy using the method of images

. Our results show that in a NINS quantum point contact the number of resonances vary with the symmetry of the order parameter. This is to be contrasted with the results for the NINS junction, in which only the position of the resonances changes with the symmetry.