Breakdown of nodal quasiparticles across the strange metal phase of Bi2201

The lineshapes of “nodal” electrons measured with photoemission spectroscopy have been used to assert that they behave as weakly interacting quasiparticles, subject to an anomalous strong damping. We quantitatively verify the consistency between the energy and momentum dependence of these line shapes for the single layer cuprate (Bi,Pb)₂(Sr,La)₂CuO_6+δ, discovering two major surprises. Firstly, below a critical doping p* the energy distribution curves are characterized by tails of spectral weight that are inconsistent with expectations based on an analysis of the momentum distribution curves at all temperatures, pointing to a breakdown of the quasiparticle paradigm. Secondly, above p* quasiparticles appear to be present in overdoped samples at very low temperature, but they lose their coherence at elevated temperature in a fashion that departs from perturbation theory. Both cases point to a genuine non-Fermi liquid behavior across the entire strange metal phase. A careful analysis of the data point to non-local self-energy corrections with a diverging energy dependence near the Fermi level as source for this non-Fermi liquid behavior.