Spin and charge dynamics of a quasi-one-dimensional antiferromagnetic metal

TL;DR

This study uses quantum Monte Carlo simulations to explore how spin and charge behaviors evolve with temperature in weakly coupled Hubbard chains, revealing a crossover from 1D Mott insulators to higher-dimensional metallic states influenced by antiferromagnetic fluctuations.

Contribution

It provides a detailed analysis of the finite-temperature dimensional crossover in quasi-1D Hubbard systems, highlighting the interplay between charge gaps, antiferromagnetic fluctuations, and metallic behavior.

Findings

Identification of a crossover between two energy scales: Mott gap and AF fluctuation gap.

Emergence of Drude-like peak indicating higher-dimensional metallic behavior.

Observation of damped spin excitations (paramagnons) near the AF wave-vector.

Abstract

We use quantum Monte Carlo simulations to study a finite-temperature dimensional-crossover-driven evolution of spin and charge dynamics in weakly coupled Hubbard chains with a half-filled band. The low-temperature behavior of the charge gap indicates a crossover between two distinct energy scales: a high-energy one-dimensional (1D) Mott gap due to the umklapp process and a low-energy gap which stems from long-range antiferromagnetic (AF) fluctuations. Away from the 1D regime and at temperature scales above the charge gap, the emergence of a zero-frequency Drude-like feature in the interchain optical conductivity $\sigma_{\perp}(\omega)$ implies the onset of a higher-dimensional metal. In this metallic phase, enhanced quasiparticle scattering off finite-range AF fluctuations results in incoherent single-particle dynamics. The coupling between spin and charge fluctuations is also seen in the spin dynamical structure factor $S({\pmb q},\omega)$ displaying damped spin excitations (paramagnons) close to the AF wave-vector ${\pmb q}=(\pi,\pi)$ and particle-hole continua near 1D momentum transfers spanning quasiparticles at the Fermi surface. We relate our results to the charge deconfinement in quasi-1D organic Bechgaard-Fabre salts.