Sn adatoms on a Si(111) substrate with 1/3 monolayer coverage form a two-dimensional triangular adatom lattice with one unpaired electron per site and an antiferromagnetic Mott insulating state. The Sn layers can be modulation hole-doped and metallized using heavily-doped p-type Si(111) substrates, and become superconducting at low temperatures. While the pairing symmetry of the superconducting state is currently unknown, the combination of repulsive interactions and frustration inherent to the triangular adatom lattice opens up the possibility for a chiral order parameter. Here, we study the superconducting state of Sn/Si(111) using scanning tunneling microscopy/spectroscopy and quasi-particle interference imaging. We find evidence for a doping-dependent Tc with a fully gapped order parameter, the presence of time-reversal symmetry breaking, and a strong enhancement of the zero-bias conductance near the edges of the superconducting domains. While each individual piece of evidence could have a more mundane interpretation, our combined results suggest the tantalizing possibility that Sn/Si(111) is an unconventional chiral d-wave superconductor.
@article{arxiv.2210.06273,
title = {Evidence for chiral superconductivity on a silicon surface},
author = {F. Ming and X. Wu and C. Chen and K. D. Wang and P. Mai and T. A. Maier and J. Strockoz and J. W. F. Venderbos and C. Gonzalez and J. Ortega and S. Johnston and H. H. Weitering},
journal= {arXiv preprint arXiv:2210.06273},
year = {2023}
}