Hidden Weyl Fermions in Paramagnetic Electride Y${}_2$C

Abstract

Recent experimental observations of Weyl fermions in materials opens a new frontier of condensed matter physics. Based on first-principles calculations, we here discover Weyl fermions in a two-dimensional layered electride material Y${}_2$C. We find that the Y 4$d$ orbitals and the anionic $s$-like orbital confined in the interstitial spaces between [Y${}_2$C]${}^{2+}$ cationic layers are hybridized to give rise to van Have singularities near the Fermi energy $E_{\mathrm{F}}$, which induce a ferromagnetic (FM) order via the Stoner-type instability. This FM phase with broken time-reversal symmetry hosts the rotation-symmetry protected Weyl nodal lines near $E_{\mathrm{F}}$, which are converted into the multiple pairs of Weyl nodes by including spin-orbit coupling (SOC). However, we reveal that, due to its small SOC effects, Y${}_2$C has a topologically nontrivial drumhead-like surface state near $E_{\mathrm{F}}$ as well as a very small magnetic anisotropy energy with several $\mu$eV per unit cell, consistent with the observed surface state and paramagnetism at low temperatures below $\sim$2 K. Our findings propose that the Brillouin zone coordinates of Weyl fermions hidden in paramagnetic electride materials would fluctuate in momentum space with random orientations of the magnetization direction.

arXiv comment9 pages, 11 figures

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• Underlying mechanism of charge transfer in Li-doped MgH${}_{16}$ at high pressure
• Interlayer Exchange Interaction Driven Topological Phase Transition in Antiferromagnetic Electride Gd${}_2$O
• Topological Fermi-arc surface state covered by floating electrons on a two-dimensional electride
• Anomalous diamagnetism of electride electrons in transition metal silicides