Going Dutch: Jan Zaanen and the strange metals consortium

Under the visionary guidance of Jan Zaanen, a group of researchers within The Netherlands formed a consortium in 2018 to explore the physics of strange metals; its core objective to determine whether strange metals represent a novel quantum critical phase and whether this phase can be described by holographic emergence principles. The consortium itself brought together theorists working on, or at the boundaries of, the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence and experimentalists with collective expertise in optical conductivity, high-field magnetotransport, scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES). For reasons that will become apparent, the experimental team chose to perform their spectroscopy and transport studies on the same crystals of a single cuprate family – (Pb,Bi)₂Sr_2-xLa_xCuO_6+δ (Bi2201). Holographic signatures were indeed found in the nodal self energies observed by ARPES. Optical conductivity and magnetotransport also found evidence for the dual character of the strange metal phase, manifest in STS as a real-space differentiation into superconducting and non-superconducting regions. The evolution of the superconducting state with temperature and doping was found to be at odds with a conventional BCS picture. This compendium of the output of that consortium serves as both a tribute to Jan's vision and perhaps, a signpost for how progress in such a complex field can be made through multiple experiments on the same material.