Unusual Hall Effect Anomaly in MnSi

Minhyea Lee, University of Colorado

The interplay between spin and charge of electrons in solids provides  a rich setting for exploring collective behavior of many interacting quantum-mechanical particles. Since its discovery more than century ago,  the Hall effect remains one of the most fundamental probes of spin-charge coupling. In a simple metal, the Hall effect arises from the deflection of electrons in the applied magnetic field, and is related to the density of carriers. In ferromagnets, the spontaneous magnetization contributes to an additional Hall current and gives rise to the so-called anomalous Hall effect. MnSi is remarkably free of impurities with a low Curie temperature and thus provides an excellent testing ground for theories of the anomalous Hall effect, not to mention the recent exciting discovery of the partial-order state at high pressure. In this talk, I present a distinct, unexpected additional contribution to the Hall effect in MnSi, which has not been observed before in helical magnetic systems. I will discuss the evidence favoring the existence of non-trivial spin texture, i.e. non-zero chirality, for the origin of the anomaly.