Giant fractional Shapiro steps have been observed in Josephson junction arrays as resulting from magnetic flux quantization in the two-dimensional array. We demonstrate experimentally the appearance of giant fractional Shapiro steps in anisotropic Josephson junction arrays as unambiguous evidence of a skewed current phase relationship. Introducing anisotropy in the array results in a giant collective high frequency response that reflects the properties of a single junction, as evidenced by the observation of a Fraunhofer like magnetic field dependence of the total critical current of the system. The observed phase dynamics can be perfectly captured within an extended resistively shunted Josephson junction model. These results directly indicate the potential of Josephson junction arrays to explore the current phase relation in a very broad frequency range (down to 50 MHz) and in a wide variety of novel link materials exhibiting non-conventional current phase relationships.

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The interaction between Aun (n=1-6) clusters and graphene is studied using first-principles simulations, based on density functional theory. The computed binding energy between Aun and graphene depends on the number of atoms in the cluster and lies between -0.6 eV and -1.7 eV, suggesting (weak) chemisorption of the clusters on graphene, rather than physisorption. Overall, the electronic properties, spin-orbit interaction and spin texture, as well as the transport properties of graphene strongly depend on the precise size of the Aun clusters. Doping of graphene is predicted for clusters with an odd number of Au atoms, due to overlap between Au s and carbon pz states close to the Fermi level. On the other hand, there is no charge transfer between even size Au clusters and graphene, but a gap is formed at the Dirac cone, due to the breaking of the pseudospin inversion symmetry of graphene’s lattice. The adsorbed Aun clusters induce spin-orbit interactions as well as spin and pseudospin interactions in graphene, as indicated by the splitting of the electronic band structure. A hedgehog spin texture is also predicted for adsorbed clusters with an even number of Au atoms. Ballistic transport simulations are performed to study the influence of the adsorbed clusters on graphene’s electronic transport properties. The influence of the cluster on the electron transmission across the structure depends on the mixing of the valence orbitals in the transport energy window. In the specific case of the Au3/graphene system, the adsorbed clusters reduce the transmission and the conductance of graphene. The Au3 clusters act as “scattering centres” for charge carriers, in agreement with recent experimental studies.

Weak link modification through current-induced atom displacement in order to tune the SQUID's response.