Strange metal transport from coupling to fluctuating spins

Abstract: Metals hosting strong electronic interactions, including high-temperature superconductors, behave in ways that do not conform to the normal Fermi liquid theory. To pinpoint the microscopic origin of this "strange metal" behavior, here we reexamine the d.c. and frequency-dependent conductivity of the two-dimensional t-J model taking advantage of recent improvements made on the finite temperature Lanczos method, enabling numerically exact calculations at unprecedentedly low temperatures and high spectral resolution. We find that strange metallicity is pervasive in the temperature-doping phase diagram wherever anti-ferromagnetic correlations are suppressed, being instead driven by paramagnetic spin fluctuations and unrelated to quantum criticality. Our results precisely characterize the Planckian carriers responsible for both the strange metal resistivities and the unconventional optical conductivities seen in experiments, highlighting striking similarities with the universal relaxation of glasses and dielectrics.