Abstract
Tin adatoms on a Si(111) substrate with a one-third monolayer coverage form a two-dimensional triangular lattice with one unpaired electron per site. These electrons order into an antiferromagnetic Mott-insulating state, but doping the Sn layer with holes creates a two-dimensional conductor that becomes superconducting at low temperatures. Although the pairing symmetry of the superconducting state is currently unknown, the combination of repulsive interactions and frustration inherent in the triangular adatom lattice opens up the possibility of a chiral order parameter. Here we study the superconducting state of Sn/Si(111) using scanning tunnelling microscopy, scanning tunnelling spectroscopy and quasiparticle interference imaging. We find evidence for a doping-dependent superconducting critical temperature with a fully gapped order parameter, the presence of time-reversal symmetry breaking and a strong enhancement in zero-bias conductance near the edges of the superconducting domains. Although each individual piece of evidence could have a more mundane interpretation, our combined results suggest the possibility that Sn/Si(111) is an unconventional chiral d-wave superconductor.
| Original language | English |
|---|---|
| Pages (from-to) | 500-506 |
| Number of pages | 7 |
| Journal | Nature Physics |
| Volume | 19 |
| Issue number | 4 |
| DOIs | |
| State | Published - Apr 2023 |
Funding
We thank C. D. Batista, P. J. Hirschfeld, P. Kent, A. Tennant and R. Zhang for fruitful discussions. The experimental work and QPI calculations were supported by the Guangdong Basic and Applied Basic Research Foundation (ref no. 2021A1515012034) and by the Office of Naval Research under grant no. N00014-18-1-2675. F.M. acknowledges support from the NSFC (no. 12174456) and the Guangdong Basic and Applied Basic Research Foundation (grant no. 2020B1515020009). C.G. acknowledges financial support from the Community of Madrid through the project NANOMAGCOST CM-PS2018/NMT-4321 and the computer resources at Centro de Computación Científica at UAM (project Biofast) as well as Altamira, with the technical support provided by the Instituto de Física de Cantabria (IFCA) via project QHS-2021-3-0005. J.O. acknowledges financial support by the Spanish Ministry of Science and Innovation through grants MAT2017-88258-R and CEX2018-000805-M (María de Maeztu Programme for Units of Excellence in R&D). The DCA calculations were supported by the Scientific Discovery through Advanced Computing (SciDAC) program funded by the US Department of Energy (DOE), Office of Science, Advanced Scientific Computing Research, and Basic Energy Sciences, Division of Materials Sciences and Engineering. This research also used resources of the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under contract DE-AC05-00OR22725.