Alejandro V. Silhanek

We have studied both theoretically and experimentally symmetric and asymmetric planar metallic Split Ring Resonators. We demonstrate that introducing structural asymmetry makes it possible to excite several higher order modes of both even (l = 2) and odd (l = 3, 5) order, which are otherwise inaccessible for a normally incident plane wave in symmetric structures. Experimentally we observe that the even mode resonances of asymmetric resonators have a quality factor 5.8 times higher than the higher order odd resonances.

We explore, with unprecedented single vortex resolution, the dissipation and motion of vortices in a superconducting ribbon under the influence of an external alternating magnetic field. This is achieved by combining the phase sensitive character of ac susceptibility, allowing us to distinguish between the inductive and dissipative responses, with the local power of scanning Hall probe microscopy. Whereas the induced reversible screening currents contribute only inductively, the vortices do leave a fingerprint in the out-of-phase component. The observed large phase-lag demonstrates the dissipation of vortices at time scales comparable to the period of the driving force (i.e., 13 ms). These results indicate the presence of slow microscopic loss mechanisms mediated by thermally activated hopping transport of vortices between metastable states.

Scanning second harmonic generation (SHG) microscopy is becoming an important tool for characterizing nanopatterned metal surfaces and mapping plasmonic local field enhancements. Here we study G-shaped and mirror-G-shaped gold nanostructures and test the robustness of the experimental results versus the direction of scanning, the numerical aperture of the objective, the magnification, and the size of the laser spot on the sample. We find that none of these parameters has a significant influence on the experimental results.

Researchers from France and Belgium use two state-of-the-art magnetic imaging techniques to reveal the patterns, annihilations, and mobilities of the vortices and antivortices in a superconducting film that they generate and manipulate with a micromagnet array and an external magnetic field.

We report that in the absence of electric dipole contributions, upon azimuthal sample rotation, the corresponding SHG response was found to be chiral, i.e. it shows the presence of asymmetries with a sense of rotation (lack of mirror symmetry). It was found that this sense of rotation reverses with the handedness configuration (G and mirror-G, see Fig. 1). While it is apparent that the property originates in local field enhancements of electric and/or magnetic multipoles, its explanation invites further theoretical research.