Surface phases of the transition metal dichalcogenide IrTe$_{2}$

Transition metal dichalcogenides have received great attention because of their fertile properties. The bulk of IrTe$_{2}$ exhibits first-order structural transitions from the expected trigonal structure at room temperature to unusual quasi-one-dimensional striped structure at low temperature. We have investigated, using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM), the surface structural properties of IrTe$_{2}$. We observe complex striped lattice modulations as a function of temperature via cooling and warming processes, including 5x1 and 8x1 phases seen in the bulk. The ground state at the surface is 6x1 phase, not seen in the bulk, and the surface transition temperatures are distinct from the bulk. The broken symmetry at the surface creates a quite different phase diagram, with the coexistence of several periodicities resembling a devil's staircase phenomena.