Superconductivity from Luttinger surfaces: Emergent $\infty$-body SYK physics

TL;DR

This paper explores how pairing on a Luttinger surface leads to a quantum critical point with thermodynamics akin to the SYK model, revealing a novel connection between non-Fermi liquids and superconductivity.

Contribution

It demonstrates that Luttinger surface models exhibit SYK-like reparametrization symmetry and gauge invariance effects, establishing a link between pair fluctuations and SYK physics.

Findings

Luttinger surface models share SYK's reparametrization symmetry.

Fluctuation propagator near QCP shows SYK-like $rac{1}{ au^{1/2}}$ behavior.

Mapping of pair fluctuations to SYK model in strong coupling limit.

Abstract

The pairing of two electrons on a Fermi surface due to an infinitesimal attraction between them always results in a superconducting instability at zero temperature ($T=0$). The equivalent question of pairing instability on a Luttinger surface (LS) -- a contour of zeros of the propagator -- instead leads to a quantum critical point (QCP) that separates a non-Fermi liquid (NFL) and superconductor. A surprising and little understood aspect of pair fluctuations at this QCP is that their thermodynamics maps to that of the Sachdev-Ye-Kitaev (SYK) model in the strong coupling limit. Here, we offer a simple justification for this mapping by demonstrating that (i) LS models share the reparametrization symmetry of the $q\rightarrow \infty$ SYK model with $q$-body interactions \textcolor{black}{close to the LS}, and (ii) the enforcement of gauge invariance results in a $\frac{1}{\sqrt{\tau}}$ ($\tau\sim T^{-1}$) behavior of the fluctuation propagator near the QCP, as is a feature of the fundamental SYK fermion.