Unconventional order parameter induced by helical chiral molecules adsorbed on a metal proximity coupled to a superconductor

Abstract

Following our previous results, which provide evidence for the emergence of a chiral p-wave tripletpairing component in superconducting Nb upon the adsorption of chiral molecules, we turned to investigate whether such an effect can take place in a proximal superconductor consisting of metal on superconductor bilayer. Note that in such proximity systems, correlated electron-hole (Andreev) pairs exist in the normal metal rather than genuine Cooper pairs. To that end, we used scanning tunneling spectroscopy (STS) on thin Au films grown in-situ on NbN (a conventional s-wave superconductor) before and after adsorbing helical chiral, alpha-helix polyalanine molecules. The tunneling spectra measured on the pristine Au surface showed conventional (s-wave like) proximity gaps. However, upon molecules adsorption the spectra significantly changed, all exhibiting a zero-bias conductance peak embedded inside a gap, indicating unconventional superconductivity. The peak reduced with magnetic field but did not split, consistent with equal-spin triplet-pairing p-wave symmetry. In contrast, adsorption of non-helical chiral cysteine molecules did not yield any apparent change in the order parameter, and the tunneling spectra exhibited only gaps free of in-gap structure.

Magnetic-related States and Order Parameter Induced in a Conventional Superconductor by Nonmagnetic Chiral Molecules

“…Most models for such topological phases demand a uniform ferromagnetic ordering; a condition that probably does not occur in our system considering the drop cast method we used to form the molecular monolayers. Indeed, our previous STM/STS studies 22,23 of chiral molecules adsorbed on Nb and Au/NbN films showed that the adsorption is not uniform and homogeneous all over the surface, although we did find islands of uniformly aligned molecules within an overall disordered molecular layer (including moleculefree regions). A similar disordered adsorption configuration was revealed also in our present STM measurements on the surface of a cleaved NbSe2 crystal (e.g., inset of Fig.…”

“…This is consistent with our previous results, described in refs. 22,23 and discussed above, suggesting that the introduction of chiral molecules modifies the order-parameter.…”

“…The inset of (a) shows an 800×800 nm 2 STM topographic image of the surface before adsorption, revealing a NbSe2 monolayer step 6-7 A high, while the inset of (b) portrays a 60×60 nm 2 STM image of the surface after adsorption, revealing a non-homogenous configuration of adsorbed molecules, akin to that found in Refs. 22,23 . The spectra presented here were all measured, correspondingly, on the regions presented by the images.…”

Functional Colloidal Assemblies Based on Superwettable Substrates

“…In addition, colloidal assembly provides an economical way of structural color development and plays an important role in fabrication of stopband materials, optic devices, sensing materials, etc., thus drawing much interest. [ 11–25 ] Among them we mainly focus on the latex assembly affording either long‐range‐order crystalline lattices or short‐range‐order glassy arrays, thus providing stable structures highly controllable within a relatively wide (ultraviolet, visible, and infrared regions) range of stopbands. Typically, colloidal assembly involves the spreading of a latex suspension onto a substrate followed by solvent evaporation‐induced latex nucleation and crystal growth.…”

Interplay between friction and spin-orbit coupling as a source of spin polarization

“…We speculate that the predicted effect has been observed with chiral molecules adsorbed on various substrates. For example, it has been shown that chiral molecules adsorbed onto s-wave superconductors induce triplet superconductivity [32][33][34], or Shiba-like states [34]. Chiral molecules on ferromagnetic surfaces induce magnetic ordering [35,36].…”