We report on the observation of the hysteretic transition of a commensurate charge modulation in IrTe 2 from transport and scanning tunneling microscopy (STM) studies. Below the transition (T C ≈ 275 K on cooling), a q ¼ 1=5 charge modulation was observed, which is consistent with previous studies. Additional modulations [q n ¼ ð3n þ 2Þ −1 ] appear below a second transition at T S ≈ 180 K on cooling. The coexistence of various modulations persists up to T C on warming. The atomic structures of charge modulations and the temperature-dependent STM studies suggest that 1=5 modulation is a periodic soliton lattice that partially melts below T S on cooling. Our results provide compelling evidence that the ground state of IrTe 2 is a commensurate 1=6 charge modulation, which originates from the periodic dimerization of Te atoms visualized by atomically resolved STM images.

We present a scanning tunneling microscopy (STM) study of the domain evolution across two first-order phase transitions of stripe modulations in IrTe 2 that occur at T C ≈ 275 K and T S ≈ 180 K, respectively. Phase coexistence of the hexagonal (1 × 1) structure and the (5 × 1) stripe modulation is observed at T C , while various (p × 1) modulations (p = 3n + 2 with 2 ≤ n ∈ N) are observed below T S . 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 IrTe 2 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.

Phase coexistence phenomena have been intensively studied in strongly correlated materials where several ordered states simultaneously occur or compete. Material properties critically depend on external parameters and boundary conditions, where tiny changes result in qualitatively different ground states. However, up to date, phase coexistence phenomena have exclusively been reported for complex compounds composed of multiple elements. Here we show that charge- and magnetically ordered states coexist in double-layer Fe/Rh(001). Scanning tunnelling microscopy and spectroscopy measurements reveal periodic charge-order stripes below a temperature of 130 K. Close to liquid helium temperature, they are superimposed by ferromagnetic domains as observed by spin-polarized scanning tunnelling microscopy. Temperature-dependent measurements reveal a pronounced cross-talk between charge and spin order at the ferromagnetic ordering temperature about 70 K, which is successfully modelled within an effective Ginzburg–Landau ansatz including sixth-order terms. Our results show that subtle balance between structural modifications can lead to competing ordering phenomena.

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