Enhanced electrical magnetochiral effect by spin-hedgehog lattice structural transition

Nonreciprocal resistance, depending on both directions of current $\mathbit{j}$ and magnetic-field $\mathbit{H}$ or magnetization $\mathbit{M}$, is generally expected to emerge in a chiral conductor and be maximized for $\mathbit{j}\phantom{\rule{4pt}{0ex}}\ensuremath{\parallel}\phantom{\rule{4pt}{0ex}}\mathbit{H}(\mathbit{M}$). This phenomenon, electrical magnetochiral effect (eMChE), is empirically known to increase with $H$ in a paramagnetic or fully ferromagnetic state on chiral lattice or to depend on fluctuation properties of a helimagnetic state. We report here the eMChE over a wide temperature range in the chiral-lattice magnet MnGe in which the spin hedgehog lattice (HL) forms with the triple spin-helix modulation vectors. The magnitude of nonreciprocal resistivity is sharply enhanced in the course of the field-induced structural transition of HL from cubic to rhombohedral form. This is attributed to the enhanced asymmetric electron scatterings by vector spin chirality in association with the large thermal fluctuations of spin hedgehogs.