Extended Data Fig. 2: Confirming ferro-rotational domains in NiTiO₃ by TEM.

(a) Selected area electron diffraction (SAED) pattern of quenched NiTiO₃ single crystal along [\(\bar{1}2\)0]. Side-view dark-field TEM images by selecting spots (b) (214) and (c) (211), showing CCW and CW ferro-rotational domains. The zone [\(\bar{1}\)20] is indexed in respect to CCW ferro-rotational domain and become zone [\(\bar{2}\)10] in respect to CW domain. Note that the Bragg spot (214) is converted into (12\(\bar{4}\)) in the reciprocal space by the twofold rotation as two ferro-rotation domains do in real space. This produces a corresponding contrast difference between the two ferro-rotational domains that allows us to uniquely confirm the existence of ferro-rotational domains.