The ‘strange metal’ is a projected Fermi liquid with edge singularities

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The first measurements on single-crystalline high-temperature superconductors revealed that the ‘normal’ metal above the superconducting transition temperature, Tc, was as unusual as the superconductor: the large, temperature-dependent resistivity implied a scattering rate not just linear in T but of the order of the average excitation energy kBT/h, where kB is Boltzmann’s constant and h is Planck’s constant. This ‘strange metal’ phase continues to be of much theoretical interest. Here we show it is a consequence of projecting the doubly occupied amplitudes out of a conventional Fermi-sea wavefunction (Gutzwiller projection), requiring no exotica such as a mysterious quantum critical point. Exploiting a formal similarity with the classic problem of Fermi-edge singularities in the X-ray spectra of metals, we find a Fermi-liquid-like excitation spectrum, but the excitations are asymmetric between electrons and holes, show anomalous forward scattering and the renormalization constant Z=0. We explain the power-law frequency dependence of the conductivity, and predict tunnelling spectrum anomalies and the forms of photoelectron spectra.