Eran Katzir

Increased superconducting transition temperature of a niobium thin film proximity coupled to gold nanoparticles using linking organic molecules.

The superconducting critical temperature, T(C), of thin Nb films is significantly modified when gold nanoparticles (NPs) are chemically linked to the Nb film, with a consistent enhancement when using 3 nm long disilane linker molecules. The T(C) increases by up to 10% for certain linker length and NP size. No change is observed when the nanoparticles are physisorbed with nonlinking molecules. Electron tunneling spectra acquired on the linked NPs below T(C) typically exhibit zero-bias peaks. We attribute these results to a pairing mechanism coupling electrons in the Nb and the NPs, mediated by the organic linkers.

Formation of Au-Silane Bonds

Many intriguing aspects of molecular electronics are attributed to organic-inorganic interactions, yet charge transfer through such junctions still requires fundamental study. Recently, there is a growing interest in anchoring groups, which considered dominating the charge transport. With this respect, we choose to investigate self-assembly of disilane molecules sandwiched between gold surface and gold nanoparticles. These assemblies are found to exhibit covalent bonds not only between the anchoring Si groups and the gold surfaces but also in plane crosslinks that increase the monolayer stability. Finally, using scanning tunneling spectroscopy we demonstrate that the disilane molecules provide strong electrical coupling between the Au nanoparticles and a superconductor substrate.

Increasing the critical temperature of Nb films by chemically linking magnetic nanoparticles using organic molecules

In type-II superconductors vortex pinning enhances the critical current density. One known method to induce pinning sites is the use of magnetic nanostructures that locally degrade the superconductivity via stray fields. In recent studies, we showed that both the critical temperature and critical current of Nb thin films can be enhanced by coupling Au nanoparticles via organic molecules and, concomitantly, a zero-bias peak appeared in the density of states. One suggested mechanism to explain these effects was the interaction of the induced pinning potential landscape with the Cooper pairs and vortices. To further examine this mechanism we study in the present work the effects of chemically linking magnetic nanoparticles to Nb films. Two types of magnetic nanoparticles are investigated, half-metal (Fe3O4) and metallic (Co). For high nanoparticle density, resulting in an effective continuous magnetic film, the critical temperature is reduced, as expected. However, for intermediate density, where the magnetic nanoparticles are well separated and a distinct pinning landscape is formed above the Nb film, critical temperature and current density enhancements are observed for both types of particles. Moreover, the tunnelling spectra acquired on the (metallic) Co nanoparticles exhibit a zero-bias conducting peak. The magnetic nanoparticles proximity through organic molecules presents similar behaviour to the non-magnetic Au nanoparticles inverse proximity results. This may suggest that pinning mechanisms play a role in the critical temperature enhancement.

Unconventional superconductivity induced in Nb films by adsorbed chiral molecules

Motivated by recent observations of chiral-induced magnetization and spin-selective transport we studied the effect of chiral molecules on conventional BCS superconductors. By applying scanning tunneling spectroscopy, we demonstrate that the singlet-pairing s-wave order parameter of Nb is significantly altered upon adsorption of chiral polyalanine alpha-helix molecules on its surface. The tunneling spectra exhibit zero-bias conductance peaks embedded inside gaps or gap-like features, suggesting the emergence of unconventional triplet-pairing components with either d-wave or p-wave symmetry at the Nb organic–molecules interface, as corroborated by simulations. These results may open a way for realizing simple superconducting spintronics devices.

Using the peak effect to pick the good organic couplers

Nanostructures are likely to become primary components of future electronic devices. Self assembled molecular electronics is a route to achieve this goal. One central issue in molecular electronics deals with charge transport across molecular elements. In this letter we present a hybrid system sensitive to the coupling and consequently to charge or energy transfer through organic molecules. Our system uses gold nanoparticles coupled through organic molecules layers to type II superconductor. We correlate the organic capping ligands of the gold nanoparticles with the vortices pinning efficiency. This sensitive phenomenon distinguishes between different organic molecules coupling efficiency.

Dynamic Control of the Vortex Pinning Potential in a Superconductor Using Current Injection through Nanoscale Patterns

Control over the vortex potential at the nanoscale in a superconductor is a subject of great interest for both fundamental and technological reasons. Many methods for achieving artificial pinning centers have been demonstrated, for example, with magnetic nanostructures or engineered imperfections, yielding many intriguing effects. However, these pinning mechanisms do not offer dynamic control over the strength of the patterned vortex potential because they involve static nanostructures created in or near the superconductor. Dynamic control has been achieved with scanning probe methods on the single vortex level but these are difficult so scale up. Here, we show that by applying controllable nanopatterned current injection, the superconductor can be locally driven out of equilibrium, creating an artificial vortex potential that can be tuned by the magnitude of the injected current, yielding a unique vortex channeling effect.