Rotation of neutron spin in passing through a noncentrosymmetric single crystal

Rotation of the spin of cold neutrons passing through a noncentrosymmetric single crystal is observed. This effect is caused by the Schwinger interaction of the magnetic moment of a moving neutron with the crystalline electric field in a noncentrosymmetric single crystal and depends both on the direction of neutron trajectory in the crystal and on its energy. It is shown that the characteristic magnitude of the effect for $\alpha$-quartz is $\simeq (1\div2)\times10^{-4}$ rad/cm over a wide wavelength range (from $2.8$ to $5.5$ Å) and is determined by the degree of beam monochromaticity [$\Delta\lambda/\lambda=(2\div5)\times10^{-2}$ in our experiment]. This magnitude corresponds to an electric field of $\simeq(0.5\div1)\times10^5$ V/cm acting on a neutron. The measured value agrees well with the theoretical calculation.