Implications of the B20 crystal structure for the magnetoelectronic structure ofMnSi

Abstract

Due to increased interest in the unusual magnetic and transport behavior of $\mathrm{MnSi}$ and its possible relation to its crystal structure (B20) which has unusual coordination and lacks inversion symmetry, we provide a detailed analysis of the electronic and magnetic structure of $\mathrm{MnSi}$. The nonsymmorphic $P{2}_{1}3$ spacegroup leads to unusual fourfold degenerate states at the zone corner $R$ point, as well as ``sticking'' of pairs of bands throughout the entire Brillouin zone surface. The resulting Fermi surface acquires unusual features as a result of the band sticking. For the ferromagnetic system (neglecting the long wavelength spin spiral) with the observed moment of $0.4{\ensuremath{\mu}}_{B}∕\mathrm{Mn}$, one of the fourfold levels at $R$ in the minority bands falls at the Fermi energy $({E}_{F})$, and a threefold majority level at $k=0$ also falls at ${E}_{F}$. The band sticking and presence of bands with vanishing velocity at ${E}_{F}$ imply an unusually large phase space for long wavelength, low energy interband transitions that will be important for understanding the unusual resistivity and far infrared optical behavior.