Evolution of the surface phase transitions in IrTe2

The phase transitions in IrTe₂ have been extensively studied but the symmetry at each phase is yet to be settled. Employing second harmonic generation (SHG) measurements over a temperature range of 4 -300 K, we probe the evolution of the symmetry of IrTe₂. Our results indicate shifts in two distinct transition temperatures (T_s1 and T_s2 with T_s1 > T_s2) through thermal cycling, providing an explanation for the variations of reported values in literature. The SHG polarimetry measurements identify symmetries in different temperature ranges, confirming the trigonal symmetry above T_s1, the triclinic symmetry between T_s1 and T_s2, and the coexistence of multiple stripe phases below T_s2. The most striking feature is the reemergence of a trigonal phase as reflected by six-fold symmetry below ~ 10 K which is likely responsible for phenomena observed at low temperatures.