118 research outputs found
Gauge Invariance and Spinon-Dopon Confinement in the t-J Model: implications for Fermi Surface Reconstruction in the Cuprates
We discuss the application of the two-band spin-dopon representation of the
t-J model to address the issue of the Fermi surface reconstruction observed in
the cuprates. We show that the electron no double occupancy (NDO) constraint
plays a key role in this formulation. In particular, the auxiliary lattice spin
and itinerant dopon degrees of freedom of the spin-dopon formulation of the t-J
model are shown to be confined in the emergent U(1) gauge theory generated by
the NDO constraint. This constraint is enforced by the requirement of an
infinitely large spin-dopon coupling. As a result, the t-J model is equivalent
to a Kondo-Heisenberg lattice model of itinerant dopons and localized lattice
spins at infinite Kondo coupling at all dopings. We show that mean-field
treatment of the large vs small Fermi surface crossing in the cuprates which
leaves out the NDO constraint, leads to inconsistencies and it is automatically
excluded form the t - J model framework
Fermi surface renormalization and quantum confinement in the two-coupled chains model
We address the problem of the Fermi surface renormalization and the quantum
confinement regime (QCR) in the two coupled chains model(TCCM) of spinless
fermions. We perform a self-consistent calculation of the renormalization
group(RG) flows of the renormalized TCCM couplings and quasiparticle weight. On
top of that we take explicitly into account the renormalization of the Fermi
surface. The flow of the difference of the renormalized Fermi wave vectors
associated with the bonding and antibonding bands has a dramatic effect on the
single particle spectrum. Although the quasiparticle amplitude is nullified
already at intermediate coupling the QCR is only observed at strong coupling.
The state associated with this regime has a charge gap and it is not a
Luttinger liquid. In contrast, the Fermi liquid regime is stabilized by the
umklapp "--like" interactions at very weak coupling regime.Comment: 9 pages, 9 figure
Insulating spin liquid in the lightly doped two-dimensional Hubbard model
We calculate the charge compressibility and uniform spin susceptibility for
the two-dimensional (2D) Hubbard model slightly away from half-filling within a
two-loop renormalization group scheme. We find numerically that both those
quantities flow to zero as we increase the initial interaction strength from
weak to intermediate couplings. This result implies gap openings in both charge
and spin excitation spectra for the latter interaction regime. When this
occurs, the ground state of the lightly doped 2D Hubbard model may be
interpreted as an insulating spin liquid as opposed to a Mott insulating state.Comment: Accepted for publication in Phys. Rev.
Self-consistent Fermi surface renormalization of two coupled Luttinger liquids
Using functional renormalization group methods, we present a self-consistent
calculation of the true Fermi momenta k_F^a (antibonding band) and k_F^b
(bonding band) of two spinless interacting metallic chains coupled by small
interchain hopping. In the regime where the system is a Luttinger liquid, we
find that Delta = k_F^b - k_F^a is self-consistently determined by Delta =
Delta_{1} [ 1 + {g}_0^2 ln (Lambda_0 / Delta)^2]^{-1} where g_0 is the
dimensionless interchain backscattering interaction, Delta_{1} is the
Hartree-Fock result for k_F^{b}-k_F^a, and Lambda_0 is an ultraviolet cutoff.
If {g}_0^2 ln (Lambda_0 / Delta_{1})^2 is much larger than unity than even weak
interachain backscattering leads to a strong reduction of the distance between
the Fermi momenta.Comment: extended version with additional technical details; 5 RevTex pages, 2
figures; to appear in Phys. Rev.
Low-energy effective representation of the Gutzwiller-projected BCS Hamiltonian close to half filling
We investigate analytically a connection between the t-J model and the
strongly correlated Bardeen-Cooper-Schrieffer (BCS) Hamiltonian, with the
effect of strong electron correlations accounted by the Gutzwiller projection.
We show that in the immediate vicinity of half filling the projected 2D BCS
Hamiltonian with strong pairing develops an antiferromagnetically (AF) ordered
ground state. This result explicitly demonstrates that antiferromagnetism in
this model appears as a natural consequence of the strong Coulomb repulsion in
a low doped regime. At moderate doping the ground state of the
Gutzwiller-projected BCS Hamiltonian becomes qualitatively similar to
Anderson's resonating valence bond state which is known to fit nicely the
properties of the t-J model in this regime. These two properties taken together
indicate that the projected BCS Hamiltonian captures the essential low-energy
physics of the t-J model in the whole underdoped region
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