Fermi surface “hot” spots in topological chiral semimetal CoSi

Materials with multifold band degeneracy provide a unique opportunity to study massless fermions without elementary particle counterparts. Recently CoSi has been shown to host both six- and four-fold band degenerate points[1,2].
Here we present a fermiology study of CoSi based on angle-resolved Shubnikov–de Haas oscillation measurements. The focused ion beam technique is used to fabricate microstructures with large length to cross section ratios to increase signal[3]. Two clear oscillation frequencies are observed at all angles. Despite the isotropic Fermi surface evident by the angle-independent oscillation frequency, the oscillation amplitude shows a sharp minimum with field applied along [100] direction, unexpected for the isotropic Fermi surfaces of a cubic material. Ab initio calculations reveal an angle-dependent electron-phonon lifetime, demonstrates the possible origin of the angle-dependent oscillation amplitude. These results indicate the existence of Fermi surface “hot” spots and its possible relation to band topology needs to be further investigated.

[1] Z. Rao et al., Nature 567, 496 (2019).
[2] D. S. Sanchez et al., Nature 567, 500–505 (2019).
[3] P. J. W. Moll, Annu. Rev. Condens. Matter Phys. 9, 147 (2018).