Visualizing anisotropic propagation of stripe domain walls in staircaselike transitions of IrTe2

We present a scanning tunneling microscopy (STM) study of the domain evolution across two first-order phase transitions of stripe modulations in IrTe2 that occur at TC≈275 K and TS≈180 K, respectively. Phase coexistence of the hexagonal (1×1) structure and the (5×1) stripe modulation is observed at TC, while various (p×1) modulations (p=3n+2 with 2≤N) are observed below TS. Using STM atomic resolution, we observe anisotropic propagation of domain boundaries along different directions, indicating significantly different kinetic energy barriers. These results are consistently explained by a theoretical analysis of the energy barrier for domain wall propagation as obtained by density functional theory. Individual switching processes observed by STM indicate that the wide temperature range of the transition from the (5×1) stripes to the (6×1)-ordered ground state is probably caused by the numerically limited subset of switching processes that are allowed between a given initial and the final state. The observations on IrTe2 are discussed in terms of a "harmless staircase" with a finite number of first-order transitions between commensurate phases and within a "dynamical freezing" scenario.