What’s Up with the Cuprates?*

It has been over thirty years since the discovery of high temperature cuprate superconductivity, and yet, despite much work, many open questions remain [1]. What is the pseudogap phase? Preformed pairs? Nematic order? Loop current order? And is the strange metal phase really a strange metal? Does it exhibit quantum critical scaling? Planckian physics? And ultimately, what is the origin of high temperature superconductivity? Can one get away with a weak coupling spin fluctuation picture, or is a liquid of singlets a more appropriate way of thinking about it? Finally, do cuprate analogues exist [2], and if so, what can they tell us that we already do not know?

[1] B. Keimer, S. A. Kivelson, M. R. Norman, S. Uchida, J. Zaanen, From Quantum Matter to High Temperature Superconductivity in Copper Oxides, Nature 518, 179 (2015).

[2] M. R. Norman, Materials design for new superconductors, Rep. Prog. Phys. 79, 074502 (2016).