Hysteretic melting transition of a soliton lattice in a commensurate charge modulation.

We report on the observation of the hysteretic transition of a commensurate charge modulation in IrTe2 from transport and scanning tunneling microscopy (STM) studies. Below the transition (TC≈275  K on cooling), a q=1/5 charge modulation was observed, which is consistent with previous studies. Additional modulations [qn=(3n+2)(-1)] appear below a second transition at TS≈180  K on cooling. The coexistence of various modulations persists up to TC 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 TS on cooling. Our results provide compelling evidence that the ground state of IrTe2 is a commensurate 1/6 charge modulation, which originates from the periodic dimerization of Te atoms visualized by atomically resolved STM images.