Nonreciprocal transmission of neutrons through the noncoplanar magnetic   system
  We report on observation of the time reversal symmetry breaking in unpolarized neutrons scattering experiment. Neutron transmittivity through the system consisting of two magnetic mirrors placed in an external magnetic field is measured. Time reversal symmetry holds for coplanar magnetic configuration, meaning that transmitted intensity does not change when interchanging neutron source and detector. Contrarily, for noncoplanar magnetic configuration the time reversal symmetry breaks down. In this case the transmitted intensity changes when interchanging the source and detector. The observed time reversal symmetry breaking is the consequence of the one of the most fundamental properties of quantum mechanics, namely the non-commutativity of spin algebra. 
D.A. Tatarskiy, A.V. Petrenko, S.N. Vdovichev, O.G. Udalov, Yu.V.   Nikitenko, A.A. Fraerman
cond-mat.mes-hall cond-mat.other