NMR Evidence for Spontaneous Electronic Chiral Order in URhSn

URhSn exhibits successive phase transitions at T_{O}=54  K and T_{C}=16  K. While the transition at T_{C} is known to be ferromagnetic, the nature of the intermediate phase between T_{O} and T_{C} has remained elusive. Here, we report ^{117}Sn nuclear magnetic resonance (NMR) measurements on high-quality single crystals of URhSn, which reveal NMR line splittings indicative of symmetry breaking in the intermediate phase. The field-direction and site dependences of these splittings are consistent with antiferroquadrupolar ordering characterized by the space group P321 (No. 150). This finding confirms the emergence of a novel form of chiral order driven by electronic degrees of freedom, without an underlying chiral crystal structure in URhSn.