Condensed Matter Seminar: "Singular density fluctuations in the strange metal phase of a copper-oxide superconductor"

Speaker Matteo Mitrano, University of Illinois at Urbana-Champaign
Date: 11/10/2017
Time: 1 p.m.

ESB 190


Physics - Condensed Matter

Event Type: Seminar/Symposium

High-temperature superconductivity often arises out of an anomalous normal state commonly referred to as a “bad” or “strange” metal, currently regarded as one of the least understood phases of matter. A fundamental hallmark of the strange metal is the lack of well-defined electron quasiparticles. In ordinary metals, quasiparticles manifest as propagating collective modes encoded in the dynamic charge susceptibility, χ(q,ω), which describes the response of the system to applied fields. However, the analogous collective modes of a strange metal are currently unknown.

In this talk, I will present the first measurement of χ(q,ω) for a prototypical strange metal, Bi2.1Sr1.9CaCu2O8+x (BSCCO), using momentum-resolved inelastic electron scattering. Our key experimental finding is the observation of 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. When moving towards the underdoped side of the phase diagram, the low-energy spectral weight is found to increase with decreasing temperature, pointing towards a monotonic doping dependence of the charge fluctuations. Our results indicate that the phenomenon underlying the strange metal is a singular form of charge dynamics of a new kind, not described by any known theory of quantum matter.

Mitrano1, A. A. Husain1, S. Vig1, A. Kogar1,2, M. S. Rak1, S. I. Rubeck1, J. Schmalian3, B. Uchoa4, J. Schneeloch5, R. Zhong5, G. D. Gu5, P. Abbamonte1

1 Department of Physics and Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA
Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Institute for the Theory of Condensed Matter, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73069, USA
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA

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