Robust broadband directional plasmons in a MoOCl2 monolayer

We predict the existence of long-lived and highly anisotropic plasmon modes in a two-dimensional molybdenum oxide dichloride ($\mathrm{MoO}{\mathrm{Cl}}_{2}$) monolayer. We show that along the $x$ direction (\ensuremath{\Gamma}-X), the plasmon modes are immune from the single-particle excitations as $q<0.255\phantom{\rule{0.16em}{0ex}}{\AA{}}^{\text{--}1}$ and the maximal energy (up to \ensuremath{\sim}2.5 eV) reaches the visible region. In the $y$ direction (\ensuremath{\Gamma}-Y) the intraband plasmons decay rapidly into electron-hole pairs as $q>0.071\phantom{\rule{0.16em}{0ex}}{\AA{}}^{\text{--}1}$, but the interband plasmons are robust in a wide range of $q$ $(0.048\phantom{\rule{0.16em}{0ex}}{\AA{}}^{\text{--}1}