Gauge-gravity duality comes to the laboratory: Evidence of momentum-dependent scaling exponents in the nodal electron self-energy of cuprate strange metals

We show that the momentum-dependent scaling exponents of the holographic fermion self-energy of the conformal-to-AdS₂ Gubser-Rocha model can describe new findings from angle-resolved photoemission spectroscopy experiments on a single-layer (Pb,Bi)₂Sr_2-xLaₓCuO_6+δ copper oxide. In particular, it was recently observed in high-precision measurements on constant energy cuts along the nodal direction that the spectral function departs from the Lorentzian line shape that is expected from the power-law-liquid model of a nodal self-energy, with an imaginary part featureless in momentum as ΣPLL^''(ω)∝(ω²)^α. By direct comparison with experimental results, we provide evidence that this departure from either a Fermi liquid or the power-law liquid, resulting in an asymmetry of the spectral function as a function of momentum around the central peak, is captured at low temperature and all dopings by a semiholographic model that predicts a momentum-dependent scaling exponent in the electron self-energy as ${{Σ}}({ω},k){∝}{ω}{({-}{{ω}}²)}^{{α}(1{-}(k{-}{k}F)/{k}F){-}1/2}$, with ${}{k}F$ the Fermi momentum.