ArXiv · 2026
Strange metals are widespread in strongly correlated quantum matter and closely intertwined with high-temperature superconductivity and quantum criticality, yet their microscopic charge dynamics remain fundamentally unresolved. Whether well-defined collective modes survive in an incoherent electronic fluid or dissolve into overdamped continua remains intensely debated. Here, employing high-momentum-resolution inelastic electron scattering complemented by direction-resolved transport, we show that the van der Waals compound MoOCl₂, a "bad" metal known to host unusually "good" plasmons, exhibits a striking dichotomy in electronic coherence and charge dynamics. Transport reveals coherent Fermi liquid behavior along one in-plane crystallographic axis and an incoherent strange metal response along the orthogonal axis. This dichotomy extends directly to the charge response. The Fermi liquid direction supports a well-defined, long-lived plasmon, whereas the strange metal direction exhibits an overdamped excitation that progressively loses its collective character with increasing momentum. Beyond a critical momentum (q_c ≈ 0.008 mathringA⁻¹), the mode undergoes a reversal into negative dispersion and ultimately collapses into a broad, nearly featureless continuum with a robust high-energy boundary (E_c ≈ 1.75 eV). Remarkably, thickness-dependent measurements show that both q_c and E_c remain nearly unchanged despite substantial modifications of Coulomb screening, revealing them as intrinsic scales of incoherent charge density fluctuations. These results establish a unique single-material platform in which coherent and incoherent electronic states are partitioned into in-plane orthogonal channels, and demonstrate that incoherent electronic fluids retain intrinsically structured charge dynamics beyond the quasiparticle paradigm.
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