Topological ground-state excitations and symmetry in the many-electron one-dimensional problem

TL;DR

This paper introduces a pseudohole basis for the Hubbard chain in a magnetic field, revealing how electron and hole excitations are composed of confined quantum objects and how they transform under symmetry operations.

Contribution

It develops a pseudohole basis that enables a comprehensive operator description of the Hubbard chain's excitations and symmetries across the entire Hilbert space.

Findings

Electron and hole excitations are composed of one c pseudohole, one s pseudohole, and one topological momenton.

Pseudohole types transform according to the symmetry group of the Hamiltonian.

Pseudohole generators for holons and spinons at half-filling are identified.

Abstract

We consider the Hubbard chain in a magnetic field and chemical potential. We introduce a pseudohole basis where all states are generated from a single reference vacuum. This allows the evaluation for all sectors of Hamiltonian symmetry of the model of the expression of the $\sigma $ electron and hole operators at Fermi momentum $\pm k_{F\sigma }$ and vanishing excitation energy in terms of pseudohole operators. In all sectors and to leading order in the excitation energy the electron and hole are constituted by one $c$ pseudohole, one $s$ pseudohole, and one {\it topological momenton}. These three quantum objects are confined in the electron or hole and cannot be separated. We find that the set of different pseudohole types which in pairs constitute the two electrons and two holes associated with the transitions from the $(N_{\uparrow }, N_{\downarrow })$ ground state to the $(N_{\uparrow }+1,N_{\downarrow })$, $(N_{\uparrow },N_{\downarrow }+1)$ and $(N_{\uparrow }-1, N_{\downarrow })$, $(N_{\uparrow },N_{\downarrow }-1)$ ground states, respectively, transform in the representation of the symmetry group of the Hamiltonian in the initial-ground-state sector of parameter space. We also find the pseudohole generators for the half-filling holon and zero-magnetic-field spinon. The pseudohole basis introduced in this paper is the only suitable for the extension of the present type of operator description to the whole Hilbert space.