Doped Spin Liquid: Luttinger Sum Rule and Low Temperature Order

TL;DR

This paper investigates a model of coupled Hubbard ladders revealing how interladder tunneling induces a semimetallic state with small Fermi pockets, affecting the Luttinger Sum Rule and leading to low-temperature order, including potential superconductivity.

Contribution

It introduces a detailed analysis of a coupled ladder model showing the impact of tunneling on Fermi surface topology and the emergence of order, extending to doped regimes with superconductivity.

Findings

Threshold tunneling induces semimetallic state with small Fermi pockets.

Sign changes in Green's function involve zeroes and infinities, affecting ARPES interpretation.

Residual interactions lead to low-temperature order and possible superconductivity.

Abstract

We analyze a model of two-leg Hubbard ladders weakly coupled by interladder tunneling. At half filling a semimetallic state with small Fermi pockets is induced beyond a threshold tunneling strength. The sign changes in the single electron Green's function relevant for the Luttinger Sum Rule now take place at surfaces with both zeroes and infinities with important consequences for the interpretation of ARPES experiments. Residual interactions between electron and hole-like quasi-particles cause a transition to long range order at low temperatures. The theory can be extended to small doping leading to superconducting order.