Anisotropic strain at atomic steps in SnTe(111)/Au(111) heterostructures revealed by moiré superlattices

Topological crystalline insulator SnTe(111) thin films offer a promising platform for strain-engineered topological phases and proximity-induced superconductivity, yet their structural response to local strain remains poorly understood. Here, we use scanning tunneling microscopy to investigate the strain landscape of SnTe(111) films grown on Au(111). We observe a coexistence of pristine and (3×3) reconstructed surfaces, along with a spontaneously formed moiré superlattice originating from interlayer twist between adjacent SnTe layers. Remarkably, the moiré period exhibits pronounced spatial variations near atomic steps on both SnTe and Au(111) surfaces. Quantitative strain mapping reveals a strain gradient of up to several percent that develops primarily perpendicular to the step direction, while the parallel component remains uniform. These findings establish the moiré superlattice as a sensitive local probe of anisotropic strain and identify few-layer SnTe(111) as a highly strain-tunable van der Waals system. Our work provides a pathway toward strain engineering of topological surface states and the design of SnTe-based quantum devices.