Two-point function of a $d=2$ quantum critical metal in the limit $k_F\rightarrow\infty$, $N_f\rightarrow 0$ with $N_fk_F$ fixed

TL;DR

This paper analyzes a 2D quantum critical metal at finite density, deriving non-perturbative fermionic and bosonic spectra in a specific double scaling limit, revealing non-Fermi-liquid behavior and limitations of RPA approximations.

Contribution

It provides the first non-perturbative analytical and numerical determination of spectra in a critical 2D metal using a double scaling limit, highlighting Landau damping effects.

Findings

Boson two-point function corrected at one-loop

Fermion spectrum exhibits non-Fermi-liquid behavior

RPA approximation does not fully capture IR physics

Abstract

We show that the fermionic and bosonic spectrum of $d=2$ fermions at finite density coupled to a critical boson can be determined non-perturbatively in the combined limit $k_F\rightarrow {\infty}$, $N_f \rightarrow 0$ with $N_fk_F$ fixed. In this double scaling limit, the boson two-point function is corrected, but only at one-loop. This double scaling limit therefore incorporates the leading effect of Landau damping. The fermion two-point function is determined analytically in real space and numerically in (Euclidean) momentum space. The resulting spectrum is discontinuously connected to the quenched $N_f\rightarrow 0$ result. For $\omega \rightarrow 0$ with $k$ fixed the spectrum exhibits the distinct non-Fermi-liquid behavior previously surmised from the RPA approximation. However, the exact answer obtained here shows that the RPA result does not fully capture the IR of the theory.