Bonding instability induced Surface Insulating State in IrTe$_{2}$

Using STM/S and DFT calculations, we find that the surface of in-situ cleaved IrTe2 undergoes a structural transition from trigonal to triclinic lattice below transition temperature, accompanied by formation of unidirectional structural modulations with distinct wavelengths. As temperature approaches 4 K, the system changes into a phase with formation of a single modulated structure with a fully-developed insulating gap. DFT rules out the CDW instability as the origin of this transition, confirming local structural distortion induced orbital degeneracy leading to strong-repulsion between Te p-band, therefore producing an insulting Te surface layer while the bulk stays metallic. This research was conducted (QL, WL, MP) at the CNMS, sponsored at ORNL by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE. Research was supported (WL, SVK) by MSED, Basic Energy Sciences, the U.S. DOE. Fellowship support (AG) from the UT/ORNL Bredesen Center for Interdisciplinary Research and Graduate Education.