Scanning SQUID Imaging of Reduced Superconductivity Due to the Effect of Chiral Molecule Islands Adsorbed on Nb

Abstract

Unconventional superconductivity was realized in systems comprising a monolayer of magnetic adatoms adsorbed on conventional superconductors, forming Shiba‐bands. Another approach to induce unconventional superconductivity and 2D Shiba‐bands was recently introduced, namely, by adsorbing chiral molecules (ChMs) on conventional superconductors, which act in a similar way to magnetic impurities as verified by conductance spectroscopy. However, the fundamental effect ChMs have on the strength of superconductivity has not yet been directly observed and mapped. In this work, local magnetic susceptometry is applied on heterostructures comprising islands of ChMs (α‐helix L‐polyalanine) monolayers adsorbed on Nb. It is found that the ChMs alter the superconducting landscape, resulting in spatially‐modulated weaker superconductivity. Surprisingly, the reduced diamagnetic response is located along the perimeter of the islands with respect to both their interior and the bare Nb. The authors suggest that topological edge‐states forming at the edges are the source of the reduced superconductivity, akin to the case of magnetic islands. The results pave new paths for the realization of topological‐superconductivity‐based devices with changing order parameter.

Chiral Induced Spin Selectivity

“…Indeed, such behavior is responsible for the response in Hall devices (Section ), magnetic force microscopy (Section ), and spin-exchange microscopy (Section ) measurements; however, other methods for detection have also been employed. For instance, superconducting quantum interference device (SQUID) magnetometry has been used to measure the effect of chiral molecules on the magnetic properties of materials; studies show that superparamagnetic iron oxide nanoparticles adsorbed on chiral self-assembled monolayers become ferromagnetic and conventional superconductors may exhibit topological superconductivity when interfaced with chiral molecules …”

“…For instance, superconducting quantum interference device (SQUID) magnetometry has been used to measure the effect of chiral molecules on the magnetic properties of materials; studies show that superparamagnetic iron oxide nanoparticles adsorbed on chiral self-assembled monolayers become ferromagnetic 92 and conventional superconductors may exhibit topological superconductivity when interfaced with chiral molecules. 93 Another technique, which has been used to probe the CISSeffect in chiral materials, is magnetic circular dichroism. Here, a magnetic field is oriented parallel or antiparallel to the direction of light and the differential adsorption of left and right circularly polarized light is measured.…”