Fermi surface studies of a non-trivial topological compound YSi

TL;DR

This study combines experimental dHvA measurements and first-principle calculations to reveal the topological nature of YSi's Fermi surface, identifying non-trivial Berry phases and symmetry-enforced Dirac points indicative of a topological metal.

Contribution

It provides the first detailed Fermi surface analysis of YSi, demonstrating its non-trivial topological features and the effects of spin-orbit coupling on its electronic structure.

Findings

Identification of a non-trivial $eta$-branch with $ ext{2D}$ character and $1.24 ext{ extpi}$ Berry phase.

Observation of a $ ext{21 T}$ frequency with non-trivial topological character and linear dispersion.

Detection of symmetry-enforced Dirac points near the Fermi energy due to spin-orbit coupling.

Abstract

The Fermi surface properties of a nontrivial system YSi is investigated by de Haas-van Alphen (dHvA) oscillation measurements combined with the first-principle calculations. Three main frequencies ($\alpha$, $\beta$, $\gamma$) are probed up to $14$~T magnetic field in dHvA oscillations. The $\alpha$-branch corresponding to $21$~T frequency possesses non-trivial topological character with $\pi$ Berry phase and a linear dispersion along $\Gamma$ to $Z$ direction with a small effective mass of $0.069~m_e$ with second-lowest Landau-level up to $14$~T. For $B~\parallel$~[010] direction, the 295~T frequency exhibits non-trivial $2D$ character with $1.24\pi$ Berry phase and a high Fermi velocity of $6.7 \times 10^5$~ms$^{-1}$. The band structure calculations reveal multiple nodal crossings in the vicinity of Fermi energy $E_f$ without spin-orbit coupling (SOC). Inclusion of SOC opens a small gap in the nodal crossings and results in nonsymmorphic symmetry enforced Dirac points at some high symmetry points, suggesting YSi to be a symmetry enforced topological metal.