Instability of a Landau Fermi liquid as the Mott insulator is approached

TL;DR

This paper investigates how a two-dimensional Fermi liquid becomes unstable and transitions into an insulating spin liquid state as it approaches a Mott insulator, highlighting the breakdown of Landau theory at specific Fermi surface points.

Contribution

It reveals the mechanism by which Umklapp processes induce strong coupling and non-Landau behavior near the Mott transition in a 2D Fermi liquid.

Findings

Strong coupling behavior at four Fermi surface points

Breakdown of Landau theory at these points

Fermi surface fragments into disconnected segments

Abstract

We examine a two-dimensional Fermi liquid with a Fermi surface which touches the Umklapp surface first at the 4 points $(\pm \pi/2, \pm \pi/2)$ as the electron density is increased. Umklapp processes at the 4 patches near $(\pm \pi/2, \pm\pi/2)$ lead the renormalization group equations to scale to strong coupling resembling the behavior of a 2-leg ladder at half-filling. The incompressible character of the fixed point causes a breakdown of Landau theory at these patches. A further increase in density spreads the incompressible regions so that the open Fermi surface shrinks to 4 disconnected segments. This non-Landau state, in which parts of the Fermi surface are truncated to form an insulating spin liquid, has many features in common with phenomenological models recently proposed for the cuprate superconductors.