Implications of the B20 Crystal Structure for the Magneto-electronic Structure of MnSi

TL;DR

This paper analyzes how MnSi's unique B20 crystal structure influences its electronic and magnetic properties, revealing unusual band degeneracies and Fermi surface features that impact its transport and optical behavior.

Contribution

It provides a detailed analysis of MnSi's electronic and magnetic structure, highlighting the effects of its non-symmorphic B20 crystal symmetry on band degeneracies and Fermi surface characteristics.

Findings

Unusual fourfold degenerate states at the R point due to B20 symmetry

Band sticking throughout the Brillouin zone surface

Presence of bands with vanishing velocity at the Fermi level

Abstract

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 non-symmorphic P2_13 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 \mu_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.