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

One-dimensional (1D) states at the step edges of solid surfaces have attracted considerable attention in a wide range of materials properties, including nanomagnetism and heterogeneous catalysis. Here, lattice strain-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 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 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.