It is found that for on-site interaction
U=0 the local
SU(2)×SU(2)×U(1) gauge symmetry of the Hubbard model on a bipartite lattice with vanishing transfer integral
t=0 can be lifted to a global
[SU(2)×SU(2)×U(1)]/Z22=SO(3)×SO(3)×U(1) symmetry in the presence of the kinetic-energy hopping term of the Hamiltonian with
t>0. The generator of the new found hidden independent charge global U(1) symmetry is one half the rotated-electron number of singly-occupied sites operator. It is confirmed elsewhere that our results have important physical consequences concerning the further understanding of the unusual properties of the hole-doped cuprates.
In this paper we review recent results on the preliminary applications of the new-found extended global SO(3) × SO(3) × U(1) symmetry of the Hubbard model on a bipartite lattice. Our results refer to the particular case of the bipartite square lattice. Specifically, we review a general description for such a model with nearest-neighbor transfer integral t and on-site repulsion U on a square lattice with N2a 1 sites consistent with its extended global symmetry. It refers to three types of elementary objects whose occupancy configurations generate the state representations of the model extended global symmetry. Such objects emerge from a suitable electron-rotated-electron unitary transformation. An application to the spin spectrum of the parent compound La2CuO4 is shortly reviewed.
In this paper a description of the Hubbard model on the square lattice with nearest-neighbor transfer integral
t, on-site repulsion
U, and
Na2≫1 sites consistent with its exact global
SO(3)×SO(3)×U(1) symmetry is constructed. Our studies profit from the interplay of that recently found global symmetry of the model on any bipartite lattice with the transformation laws under a suitable electron - rotated-electron unitary transformation of a well-defined set of operators and quantum objects. For
U/4t>0 the occupancy configurations of these objects generate the energy eigenstates that span the one- and two-electron subspace. Such a subspace as defined in this paper contains nearly the whole spectral weight of the excitations generated by application onto the zero-spin-density ground state of one- and two-electron operators. Our description involves three basic objects: charge
c fermions, spin-1/2 spinons, and
η-spin-1/2
η-spinons. Alike in chromodynamics the quarks have color but all quark-composite physical particles are color-neutral, the
η-spinon (and spinons) that are not invariant under that transformation have
η spin 1/2 (and spin 1/2) but are part of
η-spin-neutral (and spin-neutral)
2ν-
η-spinon (and
2ν-spinon) composite
ην fermions (and
sν fermions) where
ν=1,2,... is the number of
η-spinon (and spinon) pairs.The description introduced here is consistent with a Mott-Hubbard insulating ground state with antiferromagnetic long-range order for half filling at
x=0 hole concentration and a ground state with short-range spin order for a well-defined range of finite hole concentrations
x>0.