The phase diagram of the one-dimensional t-J model is investigated by analyzing the results of ex... more The phase diagram of the one-dimensional t-J model is investigated by analyzing the results of exact diagonalization and the exact solutions at J/t=0 and 2. Phase separation takes place above a critical value of J around JJt =2.5-3.5 depending on the electron density. In the small-J region, Tomonaga-Luttinger liquid theory holds and its correlation exponents are calculated as a function of J/t and the electron density. Superconducting correlations become dominant in a region between the solvable case (J/t =2) and phase separation. A spin-gap region is also found at low density.
We study statistical characterization of the many-body states in exactly solvable models with int... more We study statistical characterization of the many-body states in exactly solvable models with internal degrees of freedom. The models under consideration include the isotropic and anisotropic Heisenberg spin chain, the Hubbard chain, and a model in higher dimensions which exhibits the Mott metal-insulator transition. It is shown that the ground state of these systems is all described by that of a generalized ideal gas of particles (called exclusons) which have mutual exclusion statistics, either between different rapidities or between different species. For the Bethe ansatz solvable models, the low temperature properties are well described by the excluson description if the degeneracies due to string solutions with complex rapidities are taken into account correctly. For the Hubbard chain with strong but finite coupling, charge-spin separation is shown for thermodynamics at low temperatures. Moreover, we present an exactly solvable model in arbitrary dimensions which, in addition to giving a perspective view of spin-charge separation, constitutes an explicit example of mutual exclusion statistics in more than two dimensions.
We report a study of disordered electron systems with spin-orbit coupling on a cylinder using met... more We report a study of disordered electron systems with spin-orbit coupling on a cylinder using methods of random matrix ensembles. With a threading flux turned on, the single particle levels will generally avoid, rather than cross, each other. Our numerical study of the level-avoiding gaps in the disordered Rashba model demonstrates that the normalized gap distribution is of a universal form, independent of the random strength and the system size. For small gaps it exhibits a linear behavior, while for large gaps it decays exponentially. A framework based on matrix mechanical models is suggested, and is verified to reproduce the universal linear behavior at small gaps. Thus we propose to use the distribution of the spectral-flow gaps associated with flux insertion as a new way to characterize 2d random systems with spin-orbit coupling. The relevance and qualitative implications for spin (Hall) transport are also addressed.
In this note a lately proposed gravity dual of noncommutative Yang-Mills theory is derived from t... more In this note a lately proposed gravity dual of noncommutative Yang-Mills theory is derived from the relations, recently suggested by Seiberg and Witten, between closed string moduli and open string moduli. The only new input one needs is a simple form of the running string tension as a function of energy. This derivation provides convincing evidence that string theory integrates with the holographical principle, and demonstrates a direct link between noncommutative Yang-Mills theory and holography.
In this paper we propose the quantized spin Hall effect (SHE) in the vortex state of a rotating p... more In this paper we propose the quantized spin Hall effect (SHE) in the vortex state of a rotating p-wave paired Fermi system in an inhomogeneous magnetic field and in a weak periodic potential. It is the three dimensional extension of the spin Hall effect for a 3 He-A superfluid film studied in Ref. 1. It may also be considered as a generalization of the 3D quantized charge Hall effect of Bloch electrons in Ref. 2 to the spin transport. The A-phase of 3 He or, more generally, the p-wave paired phase of a cold Fermi atomic gas, under suitable conditions should be a good candidate to observe the SHE, because the system has a conserved spin current (with no spin-orbit couplings).
In this paper we study duality properties of the M(atrix) theory compactified on a circle. We est... more In this paper we study duality properties of the M(atrix) theory compactified on a circle. We establish the equivalence of this theory to the strong coupling limit of type IIB string theory compactified on a circle. In the M(atrix) theory context, our major evidence for this duality consists of identifying the BPS states of IIB strings in the spectrum and finding the remnant symmetry of SL(2, Z) and the associated τ moduli. By this IIB /M duality, a number of insights are gained into the physics of longitudinal membranes in the infinite momentum frame. We also point out an accidental affine Lie symmetry in the theory.
The phase diagram of the one-dimensional t-J model is investigated by analyzing the results of ex... more The phase diagram of the one-dimensional t-J model is investigated by analyzing the results of exact diagonalization and the exact solutions at J/t=0 and 2. Phase separation takes place above a critical value of J around JJt =2.5-3.5 depending on the electron density. In the small-J region, Tomonaga-Luttinger liquid theory holds and its correlation exponents are calculated as a function of J/t and the electron density. Superconducting correlations become dominant in a region between the solvable case (J/t =2) and phase separation. A spin-gap region is also found at low density.
We study statistical characterization of the many-body states in exactly solvable models with int... more We study statistical characterization of the many-body states in exactly solvable models with internal degrees of freedom. The models under consideration include the isotropic and anisotropic Heisenberg spin chain, the Hubbard chain, and a model in higher dimensions which exhibits the Mott metal-insulator transition. It is shown that the ground state of these systems is all described by that of a generalized ideal gas of particles (called exclusons) which have mutual exclusion statistics, either between different rapidities or between different species. For the Bethe ansatz solvable models, the low temperature properties are well described by the excluson description if the degeneracies due to string solutions with complex rapidities are taken into account correctly. For the Hubbard chain with strong but finite coupling, charge-spin separation is shown for thermodynamics at low temperatures. Moreover, we present an exactly solvable model in arbitrary dimensions which, in addition to giving a perspective view of spin-charge separation, constitutes an explicit example of mutual exclusion statistics in more than two dimensions.
We report a study of disordered electron systems with spin-orbit coupling on a cylinder using met... more We report a study of disordered electron systems with spin-orbit coupling on a cylinder using methods of random matrix ensembles. With a threading flux turned on, the single particle levels will generally avoid, rather than cross, each other. Our numerical study of the level-avoiding gaps in the disordered Rashba model demonstrates that the normalized gap distribution is of a universal form, independent of the random strength and the system size. For small gaps it exhibits a linear behavior, while for large gaps it decays exponentially. A framework based on matrix mechanical models is suggested, and is verified to reproduce the universal linear behavior at small gaps. Thus we propose to use the distribution of the spectral-flow gaps associated with flux insertion as a new way to characterize 2d random systems with spin-orbit coupling. The relevance and qualitative implications for spin (Hall) transport are also addressed.
In this note a lately proposed gravity dual of noncommutative Yang-Mills theory is derived from t... more In this note a lately proposed gravity dual of noncommutative Yang-Mills theory is derived from the relations, recently suggested by Seiberg and Witten, between closed string moduli and open string moduli. The only new input one needs is a simple form of the running string tension as a function of energy. This derivation provides convincing evidence that string theory integrates with the holographical principle, and demonstrates a direct link between noncommutative Yang-Mills theory and holography.
In this paper we propose the quantized spin Hall effect (SHE) in the vortex state of a rotating p... more In this paper we propose the quantized spin Hall effect (SHE) in the vortex state of a rotating p-wave paired Fermi system in an inhomogeneous magnetic field and in a weak periodic potential. It is the three dimensional extension of the spin Hall effect for a 3 He-A superfluid film studied in Ref. 1. It may also be considered as a generalization of the 3D quantized charge Hall effect of Bloch electrons in Ref. 2 to the spin transport. The A-phase of 3 He or, more generally, the p-wave paired phase of a cold Fermi atomic gas, under suitable conditions should be a good candidate to observe the SHE, because the system has a conserved spin current (with no spin-orbit couplings).
In this paper we study duality properties of the M(atrix) theory compactified on a circle. We est... more In this paper we study duality properties of the M(atrix) theory compactified on a circle. We establish the equivalence of this theory to the strong coupling limit of type IIB string theory compactified on a circle. In the M(atrix) theory context, our major evidence for this duality consists of identifying the BPS states of IIB strings in the spectrum and finding the remnant symmetry of SL(2, Z) and the associated τ moduli. By this IIB /M duality, a number of insights are gained into the physics of longitudinal membranes in the infinite momentum frame. We also point out an accidental affine Lie symmetry in the theory.
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Papers by Yong-shi Wu