Doping dependence of the spin gap in a 2-leg ladder

TL;DR

This paper investigates how doping affects the spin gap in a 2-leg ladder system using a spin-fermion model and path integral formalism, revealing that the spin gap decreases with doping, contrary to earlier mean-field results.

Contribution

It introduces a non-linear sigma model with doping-dependent couplings derived from a spin-fermion model, providing a more accurate description of doping effects on the spin gap.

Findings

Spin gap diminishes with doping.

Effective action derived from fermionic integration.

Contrasts with previous mean-field predictions.

Abstract

A spin-fermion model relevant for the description of cuprates ladders is studied in a path integral formalism, where, after integrating out the fermions, an effective action for the spins in term of a Fermi-determinant results. The determinant can be evaluated in the long-wavelength, low-frequency limit to all orders in the coupling constant, leading to a non-linear sigma model with doping dependent coupling constants. An explicit evaluation shows, that the spin-gap diminishes upon doping as opposed to previous mean-field treatments.