  Chirality of matter can produce unique responses in optics, electricity and
magnetism. In particular, magnetic crystals transmit their handedness to the
magnetism via antisymmetric exchange interaction of relativistic origin,
producing helical spin orders as well as their fluctuations. Here we report for
a chiral magnet MnSi that chiral spin fluctuations manifest themselves in the
electrical magnetochiral effect (eMChE), i.e. the nonreciprocal and nonlinear
response characterized by the electrical conductance depending on inner product
of electric and magnetic fields $\boldsymbol{E} \cdot \boldsymbol{B}$.
Prominent eMChE signals emerge at specific temperature-magnetic field-pressure
regions: in the paramagnetic phase just above the helical ordering temperature
and in the partially-ordered topological spin state at low temperatures and
high pressures, where thermal and quantum spin fluctuations are conspicuous in
proximity of classical and quantum phase transitions, respectively. The finding
of the asymmetric electron scattering by chiral spin fluctuations may explore
new electromagnetic functionality in chiral magnets.
