  Layered 5d transition metal dichalcogenide (TMD) IrTe2 is distinguished from
the traditional TMDs (such as NbSe2) by the existence of multiple CDW-like
stripe phases and superconductivity at low temperatures. Despite of intensive
studies, there is still no consensus on the physical origin of the stripe
phases or even the ground state modulation for this 5d material. Here, we
present atomic-scale evidence from scanning tunneling microscopy and
spectroscopy (STM/STS), that the ground state of IrTe2 is a q=1/6 stripe phase,
identical to that of the Se-doped compound. Furthermore, our data suggest that
the multiple transitions and stripe phases are driven by the intralayer Ir-Ir
dimerization that competes against the interlayer Te-Te bonding. The
competition results in a unified phase diagram with a series of hierarchical
modulated stripe phases, strikingly similar to the renowned "devil's staircase"
phenomena.
