Low-high voltage duality in tunneling spectroscopy of the Sachdev-Ye-Kitaev model

The Sachdev-Ye-Kitaev (SYK) model describes a strongly correlated metal with all-to-all random interactions (average strength J) between N fermions (complex Dirac fermions or real Majorana fermions). In the large-N limit a conformal symmetry emerges that renders the model exactly soluble. Here we study how the non-Fermi-liquid behavior of the closed system in equilibrium manifests itself in an open system out of equilibrium. We calculate the current-voltage characteristic of a quantum dot, described by the complex-valued SYK model, coupled to a voltage source via a single-channel metallic lead (coupling strength Γ). A one-parameter scaling law appears in the large-N conformal regime, where the differential conductance $G=dI/dV$ depends on the applied voltage only through the dimensionless combination ξ=eVJ/Γ². Low and high voltages are related by the duality G(ξ)=G(π/ξ). This provides for an unambiguous signature of the conformal symmetry in tunneling spectroscopy.