Electronic Collective Modes in the "One-Dimensional" Mott-Insulating Cuprates: Breakdown of the Spin-Charge Separation Paradigm

The collective modes (CMs) in one-dimensional (1D) cuprates are widely held to embody the spin-charge separation (SCS) innate to the 1D Hubbard model at half-filling (1DHM-HF). This paradigm was ‘solidified’ in theory after angle-resolved photoemission spectroscopy (ARPES) [1] show two distinct features in SrCuO₂ which were attributed to the light-induced hole in the photoemission process disintegrating into a continuum of charge-only (holons) and spin-only (spinons) collective modes. Here, we show, ab initio and parameter-free, the longitudinal collective modes in the 1D cuprates are Mott-gapped, pole-driven, and zero-charge/zero-spin modes agreeing quantitatively with electron and X-ray scattering. To gain insight, we downfold/upfold ab initio electronic structure to/from a low-energy space of Wannier orbitals and find the key ingredients of the CMs to be long-range screening and strong inter-plaquette chemistry —both absent in the 1DHM-HF. Additionally, long-overlooked ellipsometry data further validates this claim. Furthermore, the seminal ARPES features can be reproduced using the quasiparticle self-consistent GW (QSGW) approximation yielding a robust band theory description for the 1D cuprates.

[1] B. J. Kim, H. Koh, E. Rotenberg, S. J. Oh, H. Eisaki, N. Motoyama, S. Uchida, T. Tohyama, S. Maekawa, Z. X. Shen, et al., Nature Physics 2, URL https://www.osti.gov/biblio/889174.