Skyrmions, emergent magnetic monopoles, and their electromagnetic responses in cubic chiral magnets

Topological spin crystals can give rise to versatile electromagnetic responses through the interplay of conduction electrons and scalar-spin chirality (SSC) [1]. Among them, emergent magnetic monopoles formed in a cubic chiral magnet MnGe exhibit intriguing transport phenomena due to static and dynamic SSC, which can be controlled by external magnetic field [2]. In particular, the dynamics of emergent magnetic monopoles generate unique electronic functions such as enhanced magneto-resistivity, magneto-Seebeck effect, or magneto-chiral effect. Furthermore, a gigantic anomalous Hall effect (AHE) showing a Hall conductivity of ~40,000 Ω^-1cm^-1 and a Hall angle of ~18 % is identified, which can hardly be explained by conventional mechanisms of intrinsic and extrinsic AHE [3]. All these unusual phenomena will be discussed in the light of magnetic fluctuations and novel electron scattering process upon unwinding of the dense topological spin singularities. The formation mechanism of emergent magnetic monopoles will also be discussed, highlighting the role of conduction-electron mediated exchange interactions (e.g. RKKY and related higher-order spin interactions), which is also supported by the experimental observation of skyrmion-monopole transition induced by chemical pressure control in MnSi_1-xGe_x [4].