Gauge-gravity duality comes to the lab: 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-AdS_2 Gubser-Rocha model can describe new findings from angle-resolved photoemission spectroscopy experiments on a single layer (Pb,Bi)_2Sr_2-xLa_xCuO_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 Σ”_PLL(ω) ∝ (ω^2)^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 semi-holographic 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 ħ k_F the Fermi momentum.