Giant magnetoresistance, Fermi-surface topology, Shoenberg effect, and vanishing quantum oscillations in the type-II Dirac semimetal candidates MoSi2 and WSi2

We performed comprehensive theoretical and experimental studies of the electronic structure and the Fermi surface topology of two novel quantum materials, $\mathrm{Mo}{\mathrm{Si}}₂$ and $\mathrm{W}{\mathrm{Si}}₂$. The theoretical predictions of the electronic structure in the vicinity of the Fermi level was verified experimentally by thorough analysis of the observed quantum oscillations in both electrical resistivity and magnetostriction. We established that the Fermi surface sheets in $\mathrm{Mo}{\mathrm{Si}}₂$ and $\mathrm{W}{\mathrm{Si}}₂$ consist of 3D dumbbell-shaped holelike pockets and rosette-shaped electronlike pockets, with nearly equal volumes. Based on this finding, both materials were characterized as almost perfectly compensated semimetals. In conjunction, the magnetoresistance attains giant values of ${10}⁴$ and ${10}⁵%$ for $\mathrm{W}{\mathrm{Si}}₂$ and $\mathrm{Mo}{\mathrm{Si}}₂$, respectively. In turn, the anisotropic magnetoresistance achieves $\ensuremath{-}95%$ and $\ensuremath{-}98%$ at $T=2$ K and in $B=14$ T for $\mathrm{W}{\mathrm{Si}}₂$ and $\mathrm{Mo}{\mathrm{Si}}₂$, respectively. Furthermore, for both compounds we observed the Shoenberg effect in their Shubnikov-de Haas oscillations that persisted at as high temperature as $T=25$ K in $\mathrm{Mo}{\mathrm{Si}}₂$ and $T=12$ K in $\mathrm{W}{\mathrm{Si}}₂$. In addition, we found for $\mathrm{Mo}{\mathrm{Si}}₂$ a rarely observed spin-zero phenomenon. Remarkably, the electronic structure calculations revealed type-II Dirac cones located near 480 and 710 meV above the Fermi level in $\mathrm{Mo}{\mathrm{Si}}₂$ and $\mathrm{W}{\mathrm{Si}}₂$, respectively.