D. N. Sheng

PHASE STRING EFFECT IN THE T-J MODEL : GENERAL THEORY

We reexamine the problem of a hole moving in an antiferromagnetic spin background and find that the injected hole will always pick up a sequence of nontrivial phases from the spin degrees of freedom. Previously unnoticed, such a stringlike phase originates from the hidden Marshall signs which are scrambled by the hopping of the hole. We can rigorously show that this phase string is nonrepairable at low energy and give a general proof that the spectral weight Z must vanish at the ground-state energy due to the phase-string effect. Thus, the quasiparticle description fails here and the quantum interference effect of the phase string dramatically affects the long-distance behavior of the injected hole. We introduce a so-called phase-string formulation of the t-J model for a general number of holes in which the phase-string effect can be explicitly tracked. As an example, by applying this new mathematical formulation in one dimension, we reproduce the well-known Luttinger-liquid behaviors of the asymptotic single-electron Greens function and the spin-spin correlation function. We can also use the present phase-string theory to justify previously developed spin-charge separation theory in two dimensions, which offers a systematic explanation for the transport and magnetic anomalies in the high-

Phase diagram of the integer quantum Hall effect

{mathrm{T}}_{mathrm{c}}

MEAN-FIELD DESCRIPTION OF THE PHASE STRING EFFECT IN THE T-J MODEL

cuprates.

Spin-charge separation in the t-J model: Magnetic and transport anomalies.

The phase diagram of the integer quantum Hall effect is numerically determined in the tight-binding model, which can account for overall features of recently obtained experimental phase diagram with direct transitions from high plateau states to the insulator. In particular, the quantum Hall plateaus are terminated by two distinct insulating regimes, characterized by the Hall resistance with classic and quantized values, respectively, which is also in good agreement with experiments. The physical origin of this peculiar phase diagram is discussed.

THEORY OF FERROMAGNETIC METAL TO PARAMAGNETIC INSULATOR TRANSITION IN R1-XAXMNO3

A mean-field treatment of the phase string effect in the

REFLECTION SYMMETRY AND QUANTIZED HALL RESISTIVITY NEAR THE QUANTUM HALL TRANSITION

t-J

Nature of spin-charge separation in the t-J model

model is presented. Such a theory is able to unite the antiferromagnetic (AF) phase at half-filling and metallic phase at finite doping within a single theoretical framework. We find that the low-temperature occurrence of the AF long range ordering (AFLRO) at half-filling and superconducting condensation in metallic phase are all due to Bose condensations of spinons and holons, respectively, on the top of a spin background described by bosonic resonating-valence-bond (RVB) pairing. The fact that both spinon and holon here are bosonic objects, as the result of the phase string effect, represents a crucial difference from the conventional slave-boson and slave-fermion approaches. This theory also allows an underdoped metallic regime where the Bose condensation of spinons can still exist. Even though the AFLRO is gone here, such a regime corresponds to a microscopic charge inhomogeneity with short-ranged spin ordering. We discuss some characteristic experimental consequences for those different metallic regimes. A perspective on broader issues based on the phase string theory is also discussed.

Topological characterization of delocalization in a spin-orbit coupling system.

A real spin-charge separation scheme is found based on a saddle-point state of the {ital t}-{ital J} model. In the one-dimensional (1D) case, such a saddle-point reproduces the correct asymptotic correlations at the strong-coupling fixed point of the model. In the two-dimensional (2D) case, the transverse gauge field confining spinon and holon is shown to be gapped at {ital finite} {ital doping} so that a spin-charge deconfinement is obtained for its first time in 2D. The gap in the gauge fluctuation disappears at half-filling limit, where a long-range antiferromagnetic order is recovered at zero temperature and spinons become confined. The most interesting features of spin dynamics and transport are exhibited at finite doping where exotic {ital residual} couplings between spin and charge degrees of freedom lead to systematic anomalies with regard to a Fermi-liquid system. In spin dynamics, a commensurate antiferromagnetic fluctuation with a small, doping-dependent energy scale is found, which is characterized in momentum space by a Gaussian peak at ({pi}/{ital a},{pi}/{ital a}) with a doping-dependent width. This commensurate magnetic fluctuation contributes a non-Korringa behavior for the NMR spin-lattice relaxation rate. There also exists a characteristic temperature scale below thich a pseudogap behavior appears in the spin dynamics. Furthermore,morexa0» an incommensurate magnetic fluctuation is also obtained at a {ital finite} energy regime. In the transport, a strong-range phase intereference leads to an effective holon Lagrangian which can give rise to a series of interesting phenomena including linear-{ital T} resistivity and a {ital T}{sup 2} Hall angle. We discuss the striking similarities of these theoretical features with those found in the high-{ital T}{sub {ital c}} cuprates and give a consistent picture for the latter. Electronic properties like Fermi surface and superconducting pairing in this framework are also discussed.«xa0less

Spin-charge separation: from one hole to finite doping

The double-exchange model for the Mn oxides with orbital degeneracy is studied with including on-site Coulomb repulsion, Jahn-Teller (J-T) coupling and doping-induced disorder. In the strong interaction limit, it is mapped onto a single-band Anderson model, in which all scattering mechanisms can be treated on an equal footing. A sharp rise in the mean square fluctuation of lattice distortions is found near the Curie temperature

Understanding high-Tc cuprates based on the phase string theory of doped antiferromagnet

T_c