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Induced unconventional superconductor order parameter in a proximity layer coated with chiral molecules


  Tamar Shapira  ,  Hen Alpern [1,2]  ,  Shira Yochelis [2]  ,  Gad Koren [3]  ,  Yossi Paltiel [2]  ,  Oded Millo [1]  
 [1] Racah Institute of Physics and the Center for Nanoscience and Nanothechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
[2] Applied Physics Department and the Center for Nanoscience and Nanothechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
[3] Department of Physics, Technion - Israel Institute of Technology, Haifa 32000, Israel

Following our previous results [1] that provide evidence for the emergence of a triplet-pairing chiral p-wave superconducting component in Nb upon the adsorption of chiral molecules, we turned to investigate whether such an effect can take place in a proximal superconductor. Note that in such proximity systems correlated electron-hole (Andreev) pairs exist instead of real Cooper pairs. To that end, we applied scanning tunneling spectroscopy (STS) on thin Au films grown expitaxially onto NbN (a conventional s-wave superconductor) before and after adsorbing chiral polyalanine alpha-helix 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, exhibiting zero-bias conductance peaks embedded inside gaps. These results suggest the emergence of unconventional superconductivity with sing-changing order-parameter, consistent, here too, with triplet-pairing p-wave symmetry. These results may open a way for realizing simple superconducting spintroinics devices.

 [1] H. Alpern, E. Katzir, S. Yochelis, N. Katz, Y. Paltiel, and O. Millo, New J. Phys. 18, 113048 (2016)