Featured Research

Strange Metals Get Stranger

Posted: June 08, 2018

Phase diagram of the cuprates, temperature versus doping. The strange metal phase (SM) lays above the superconducting dome region (SC). In that phase, the Fermi liquid picture (FL) breaks down.

The strange metal is a poorly understood state of matter found in a variety of quantum materials, notably both Cu- and Fe-based high-temperature superconductors. This phase is believed to be key for the understanding of superconductivity in those materials, which have been observed at record high temperatures. OU Professor Bruno Uchoa coauthored a paper published in the Proceedings of the National Academy of Sciences with an experimental group from the University of Illinois. In this work, it is found experimental evidence that this phase exhibits a property called “local scale invariance”, which seems to challenge previous assumptions about this state.

Strange metals exhibit a non-saturating electrical resistivity that scales linearly with temperature, suggesting the absence of electron quasiparticles, the elementary excitations of the Fermi sea. This property is at odds with conventional Fermi liquids, justifying the “strangeness” of this phase. Using inelastic electron scattering, this study reports for the first time the momentum-resolved measurement of the dynamical charge fluctuations of optimally doped Bi2.1Sr1.9CaCu2O8+x. The results suggest that it does not exhibit propagating collective modes, such as the plasmon excitation of normal metals, but instead shows a featureless charge response lacking either temperature or momentum dependence. The charge dynamics in the strange metal is found to be made of purely local excitations in which the space and time axes are entirely decoupled. The findings indicate that this state is defined by a singular kind of charge dynamics for which there is no generally accepted theory. 

See also: http://www.pnas.org/content/115/21/5392