Nature of spin-charge separation

TL;DR

This paper investigates the effects of spin-charge separation and phase shifts in the $t-J$ model, revealing how they influence quasiparticle stability, Fermi surface structure, and the nature of the underdoped regime in high-temperature superconductors.

Contribution

It introduces a comprehensive effective theory incorporating phase shift effects, clarifying quasiparticle stability and Fermi surface topology in spin-charge separated states.

Findings

Phase shift causes non-Fermi liquid behavior as conjectured by Anderson.

Injected holes remain stable due to confinement by phase shift, except at zero doping.

Fermi surface transitions from large to four Fermi points with doping.

Abstract

Quasiparticle properties are explored in an effective theory of the $t-J$ model which includes two important components: spin-charge separation and unrenormalizable phase shift. We show that the phase shift effect indeed causes the system to be a non-Fermi liquid as conjectured by Anderson on a general ground. But this phase shift also drastically changes a conventional perception of quasiparticles in a spin-charge separation state: an injected hole will remain {\em stable} due to the confinement of spinon and holon by the phase shift field despite the background is a spinon-holon sea. True {\em deconfinement} only happens in the {\em zero-doping} limit where a bare hole will lose its integrity and decay into holon and spinon elementary excitations. The Fermi surface structure is completely different in these two cases, from a large band-structure-like one to four Fermi points in one-hole case, and we argue that the so-called underdoped regime actually corresponds to a situation in between, where the ``gap-like'' effect is amplified further by a microscopic phase separation at low temperature. Unique properties of the single-electron propagator in both normal and superconducting states are studied by using the equation of motion method. We also comment on some of influential ideas proposed in literature related to the Mott-Hubbard insulator and offer a unified view based on the present consistent theory.