Spin-Orbital Separation in the quasi 1D Mott-insulator Sr2CuO3

TL;DR

This study demonstrates the separation of spin, charge, and orbital degrees of freedom in a 1D Mott insulator, revealing orbiton propagation as a distinct quasi-particle using advanced X-ray scattering techniques.

Contribution

It provides experimental evidence of orbital degree separation in a 1D Mott insulator, extending the concept of spin-charge separation to include orbitons.

Findings

Observation of orbiton separation from spinons.

Detection of orbiton propagation with ~0.2 eV dispersion.

Confirmation of quantum number separation in 1D Mott insulators.

Abstract

As an elementary particle the electron carries spin \hbar/2 and charge e. When binding to the atomic nucleus it also acquires an angular momentum quantum number corresponding to the quantized atomic orbital it occupies (e.g., s, p or d). Even if electrons in solids form bands and delocalize from the nuclei, in Mott insulators they retain their three fundamental quantum numbers: spin, charge and orbital[1]. The hallmark of one-dimensional (1D) physics is a breaking up of the elementary electron into its separate degrees of freedom[2]. The separation of the electron into independent quasi-particles that carry either spin (spinons) or charge (holons) was first observed fifteen years ago[3]. Using Resonant Inelastic X-ray Scattering on the 1D Mott-insulator Sr2CuO3 we now observe also the orbital degree of freedom separating. We resolve an orbiton liberating itself from spinons and propagating through the lattice as a distinct quasi-particle with a substantial dispersion of ~0.2 eV.