High temperature superconductivity and the Catch-22 conundrum

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CATCH-22 sets out to resolve the mystery of the cuprate high temperature superconductors. Hailed as one of the major discoveries of the 20th Century, its central mysteries – the pairing mechanism, the origin of the ‘pseudogap’ and the nature of the ‘strange metal’ phase, have remained elusive for over 30 years. Typically, what scatters electrons also binds them into pairs, and in the cuprates, the strong pairing interaction manifests itself in the strange metal phase as intense scattering, so strong in fact that it drives the electronic states required for pairing incoherent. In other words, what first promotes high temperature superconductivity ultimately destroys it! This logical paradox is the Catch-22 conundrum. CATCH-22, the program, comprises three parts. Part 1 will explore the fate of electronic states within the strange metal phase by studying how the metallic response diminishes across universal bounds, both as a function of temperature and interaction strength, through momentum-averaged electrical conductivity and thermal diffusivity studies and momentum-resolved photoemission spectroscopy. Part 2 will seek to access the ground state of optimally doped cuprates for the first time, by applying intense current and laser pulses to ultra-thin samples in a high magnetic field. The latter, if successful, will open up a new frontier in which intense THz light and intense magnetic fields combine to access the terra incognita of hidden phases. Finally, Part 3 will explore the origins of the strange metal at the edge of the superconducting dome and search for manifestations of incoherence in other strange metals in an attempt to unify the governing principles. Given that the central mysteries are intertwined – the strange metal is a precursor to the pseudogap which in turn leads to superconductivity - CATCH-22 will aim to bring significant new insight into all three and pave the way, finally, for a coherent phenomenological model for cuprate superconductivity.