Good plasmons in a bad metal
Francesco L. Ruta, Yinming Shao, Swagata Acharya, Anqi Mu, Na Hyun Jo, Sae Hee Ryu, Daria A. Balatsky, Yifan Su, Dimitar Pashov, Brian S. Y. Kim, M. I. Katsnelson, James G. Analytis, Eli Rotenberg, Andrew J. Millis, Mark van Schilfgaarde, D. N. Basov
Abstract
Correlated metals may exhibit unusually high resistivity that increases linearly in temperature, breaking through the Mott-Ioffe-Regel bound, above which coherent quasiparticles are destroyed. The fate of collective charge excitations, or plasmons, in these systems is a subject of debate. Several studies have suggested that plasmons are overdamped, whereas other studies have detected propagating plasmons. In this work, we present direct nano-optical images of low-loss hyperbolic plasmon polaritons (HPPs) in the correlated van der Waals metal MoOCl 2 . HPPs are plasmon-photon modes that waveguide through extremely anisotropic media and are remarkably long-lived in MoOCl 2 . Photoemission data presented here reveal a highly anisotropic Fermi surface, reconstructed and made partly incoherent, likely through electronic interactions as explained by many-body theory. HPPs remain long-lived despite this, revealing previously unseen imprints of many-body effects on plasmonic collective modes.