One-dimensional edge state induced by strain in a monolayer copper nitride on Cu(001)

Abstract

One-dimensional (1D) states at step edges of solid surfaces have attracted considerable interest in a wide range of materials properties, including nanomagnetism and heterogeneous catalysis. Here, a lattice-stain-induced 1D electronic states at the step edges of the nitrogen (N)-saturated Cu(001) surface are reported on the basis of low-temperature scanning tunneling microscopy observations and theoretical calculations. The 1D state appears along the step edge of the upper nanoterrace, where the surface Cu₂N lattice is locally expanded. The observed standing waves confined on rectangular terraces are well reproduced by numerical simulations for a model of the 1D electrons confined in a box with a triangular edge potential well. The emergence of the edge 1D state is attributed to the strain-dependent energy shift of the N-derived two-dimensional band on the surface using the calculations based on the density functional theory. Further theoretical analysis reveals that the direction of the band energy shift depends on the orbital character of the surface band.