Surface phases of the transition-metal dichalcogenide IrTe2

Transition-metal dichalcogenide IrTe2 has attracted attention because of striped lattice, charge ordering and superconductivity. We have investigated the surface structure of IrTe2, using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). A complex striped lattice modulations as a function of temperature is observed, which shows hysteresis between cooling and warming. While the bulk 5x1 and 8x1 phases appear at high temperatures, the surface ground state has the 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 devil's staircase behavior.