Disappearance of the quasi-one-dimensional plasmon at the metal-insulator phase transition of indium atomic wires

An array of indium atomic wires on Si(111) exhibits a temperature-induced phase transition between (4×1) and (8×2) structures, both of which were investigated by using electron energy loss spectroscopy (EELS). The EELS spectra of the (4×1) phase taken at room temperature show a clear momentum-dependent energy loss peak, which is assigned to the one-dimensional (1D) plasmon originating from 1D metallic electronic state of the In atomic wires. In the (8×2) structure at 80 K, in contrast, the plasmon peak completely disappears. This result is explained by the wide gap opening of the 1D electronic band at the Fermi energy at the metal-insulator transition between the (4×1) and (8×2) structures.