Academic & Research

Recomputing the quartet phase diagram of an earlier study, I found a region where quartet correlations vanish exactly — missed by the original publication — and traced it to a doublet ground state.

GAL tracks exact NRG almost perfectly in the strongly correlated regime and at weaker couplings, but cannot produce the triplet ground state NRG finds. Knowing where an approximation breaks is what makes it usable.

Current–phase analysis of a three-lead junction, locating the “sweet line” of couplings where the OFF supercurrent vanishes and switching becomes ideal — calculations that grew into an article of its own.

Python scripts on top of the Kwant package: define the honeycomb lattice site by site, attach leads, and compute band structures, conductance curves and local densities of states for zigzag and armchair graphene nanoribbons, from a single ring of atoms up to ribbons three hundred rings wide. The complete scripts are printed in the thesis appendix, so every figure can be rerun.

Armchair ribbons came out metallic only at the widths the known 3M − 1 rule allows, semiconducting otherwise with the gap closing as ribbons widen; zigzag ribbons conducted at every width through a zero-energy state living on their edges, which fades away in the infinite-width graphene limit. Nothing new here: the point was making the machinery agree with the literature.

A single-atom vacancy breaks the lattice's bipartite symmetry: the conductance loses its symmetry around zero energy and the edge-state density of states is wiped out. The effect is pronounced in narrow ribbons and barely registers in wide ones. A modest, expected result, reported as such.