Fermi surface studies of YSi from dHvA oscillations and first principles calculations

Topologically nontrivial compounds are enormously explored for their novel symmetry protected bulk and surface states. We present our experimental results on the Fermi surface study of YSi using de Haas-van Alphen (dHvA) oscillations combined with theoretical first principles calculations. The fast Fourier transform of the dHvA oscillations has revealed three frequencies α, β, and γ for B || [010] at 36 T, 295 T, and 61T, respectively. For other two configurations of magnetic field B || [100] and B || [001], quantum oscillations are observed only for α pocket. Further quantum oscillations simulation confirms the two-dimensional character of the β and γ pockets whereas α pocket is existing along all three directions. The estimated Berry phase of α pocket is 0.52p and 1.39p for B || [100] and [001], which gives the non-trivial character of α band. From the first principles calculations, in the absence of spin-orbit coupling (SOC) nodal line crossings are observed along various high symmetry paths whereas inclusion of spin-orbit coupling opens a small gap between the bands along the generic directions and symmetry enforced robust Dirac states are obtained at time reversal invariant points.