Understanding solitonic excitations in the charge density wave ordered ground state of the In/Si(111) nanowire array from phonon theory*

The Si(111)-(4x1)/(8x2)In atomic wire array is an extremely popular model system for one-dimensional electronic systems. It features a reversible temperature-induced metal-insulator transition into a charge density wave (CDW) ordered ground state. Solitonic excitations of the CDW and associated topological edge states are presently the focus of increasing attention. We carried out a combined ab initio and scanning tunneling microscopy (STM) study of solitonic phase defects in the In/Si(111) atomic wire array. We show how the solitonic CDW excitations can be modeled in terms of collective excitations of particular phonon modes. In conjunction with STM measurements, this phonon expansion approach allows us for the first time to determine the atomistic structure of the solitonic excitations. Due to the topological properties of the solitons and a strongly non-linear phonon-phonon coupling, these solitons interact in a deterministic way and are suitable for information processing.