Peter Abbamonte (SIMES Seminar)

Date(s) - Oct 13 2017
8:30 AM - 9:30 AM

Room 335, McCullough Building


Singular density fluctuations in the strange metal phase of Bi2Sr2CaCu2O8+x observed with momentum-resolved EELS (M-EELS)

  Peter Abbamonte

University of Illinois, Urbana, IL

High-temperature superconductivity arises out of an anomalous normal state commonly referred to as a “bad” or “strange” metal, since it lacks the usual signatures of electron quasiparticles. In ordinary metals, such quasiparticles manifest as propagating collective modes encoded in the dynamic charge susceptibility c²(q,w), which describes the response of the system to applied fields. However, the analogous collective modes of a strange metal are currently unknown.  Here, we present the first measurement of c²(q,w) for a prototypical strange metal, Bi2.1Sr1.9CaCu2O8+x (BSCCO), using momentum-resolved inelastic electron scattering (M-EELS). We discover a surprising energy- and momentum-independent continuum of fluctuations extending up to 1 eV, at odds with the dispersive plasmons expected in normal metals. This spectrum is found to be temperature-independent across the superconducting phase transition at optimal doping. Tuning the composition to overdoping, where a crossover to Fermi liquid behavior is expected, this momentum-independent continuum is found to persist, though a 0.5 eV gap-like feature now emerges at low temperature. Our results indicate that the phenomenon underlying the strange metal is a singular form a charge dynamics of a new kind, that does not fit into any known picture of quantum critical scaling.