CATCH-22 sets out to resolve the mystery of the copper-oxide high temperature superconductors. Hailed as one of the major discoveries of the 20th Century in physics, 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. The stark failure to explain these phenomena using conventional theories have led to a consensus that the cuprates represent fundamentally new states of matter that require a radically new theoretical framework.
Typically, what scatters electrons in their metallic state also binds them into pairs. In the cuprates, the strong pairing interaction, of as yet unknown origin, manifests itself in the strange metal phase as intense scattering, so strong in fact that it drives the coherent electronic states required for pairing to the edge of incoherence. In other words, what first promotes high temperature superconductivity ultimately destroys it! Within literary circles, such a logical paradox is known as the Catch-22 conundrum.
CATCH-22, the program, comprises three parts. The focus of Part 1 will be the incoherent transport regime in which the fate of electronic states within the strange metal phase will be determined. A dedicated study of decoherence in cuprates is long overdue. CATCH-22 will seek to demystify the strange metal by studying how the metallic response disintegrates across universal bounds, both as a function of temperature and doping (interaction strength), through a combination of momentum-averaged electrical, optical and thermal conductivity studies in high magnetic fields with momentum-resolved photoemission spectroscopy. Part 2 will seek to access the electronic ground state of optimally doped cuprates for the first time, using THz spectroscopy and pulsed high-current measurements on ultra-thin samples in magnetic fields up to 45 T and 90 T respectively. The latter, if successful, will open up a new frontier in the exploration of unconventional superconductors and other correlated systems in which intense THz light and intense magnetic fields combine to access the ‘terra incognita’ of hidden phases. Finally, in Part 3, we will explore the origins of the strange metal at the edge of the superconducting dome and search for manifestations of incoherence in other candidate strange metals in an attempt to establish the paradigm for strange metal behaviour.
Given that the central mysteries are intertwined – the strange metal is a precursor to the pseudogap which in turn leads to superconductivity - CATCH-22 has the potential to bring significant new insight into all three and pave the way, finally, for the development of a coherent explanation of the cuprate phenomenon.
