Nearly Perfect Fluidity in a High Temperature Superconductor

TL;DR

This study demonstrates that a high-temperature superconductor exhibits nearly perfect fluidity, with a low shear viscosity to entropy density ratio, similar to exotic states like quark-gluon plasma.

Contribution

First measurement of electronic analogue of {}/s in a high-temperature superconductor using ARPES, revealing nearly perfect fluid behavior above Tc.

Findings

Superconductor exhibits nearly perfect fluidity around Tc.

Electronic {}/s ratio is comparable to that of quark-gluon plasma.

Fluid-like behavior persists above the superconducting transition temperature.

Abstract

Perfect fluids are characterized as having the smallest ratio of shear viscosity to entropy density, {\eta}/s, consistent with quantum uncertainty and causality. So far, nearly perfect fluids have only been observed in the Quark-Gluon Plasma (QGP) and in unitary atomic Fermi gases (UFG), exotic systems that are amongst the hottest and coldest objects in the known universe, respectively. We use Angle Resolve Photoemission Spectroscopy (ARPES) to measure the temperature dependence of an electronic analogue of {\eta}/s in an optimally doped cuprate high temperature superconductor, finding it too is a nearly perfect fluid around, and above, its superconducting transition temperature Tc.