Atomistic Origin Of Metal Versus Charge-Density-Wave Phase Separation In Indium Atomic Wires On Si(111)

We investigate in atomic scale the electronic phase separation occurring in the well known quasi-one-dimensional (quasi-1D) charge-density wave (CDW) phase of an In atomic wire array on a Si(111) surface. The characteristic atomic scale defects, originating from excess In atoms, are found to be actively involved in the formation of the phase boundary between the metallic and the CDW phases by extensive analysis of scanning tunneling microscopy images at various temperatures. These particular defects flip the phase of the quasi-1D CDW to impose strong local constraints in the CDW correlation. We show that such local constraints and the substantial interwire CDW interaction induce local condensates of CDW and the phase separation between the metallic and the CDW phases. This work unveils the atomistic origin of the electronic phase separation, highlighting the importance of atomic scale structures of defects and their collective interaction in electronically inhomogeneous materials.