Implications of the B20 crystal structure for the magnetoelectronic structure of MnSi

Due to increased interest in the unusual magnetic and transport behavior of 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 MnSi. The nonsymmorphic P2(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 0.4mu(B)/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.