The normal state of unconventional superconductors often exhibits anomalous transport properties, and it is commonly referred to as a “bad” or “strange” metal. Understanding its collective charge dynamics, which defies the standard quasiparticle description of a Fermi liquid, is an outstanding challenge of modern condensed matter physics. In this talk, I will present direct measurements of the collective charge dynamics of the strange metal using inelastic electron scattering. First, I will discuss how normal-state Bi2Sr2CaCu2O8+δ is defined by a featureless, localized continuum, undergoing a massive, low-temperature spectral weight redistribution,. I will then describe how such a phase is found to coexist with a low-energy Fermi liquid in Sr2RuO4. These results indicate that strange metal fluctuations are highly localized and strongly dissipative, however they do not necessarily exclude the existence of a low-energy/low-momentum Fermi liquid. Implications for various theories of the strange metal phase will also be discussed.
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