Yasuhiro Saiga

Electron Addition Spectrum in the Supersymmetric t-J Model with Inverse-Square Interaction

The electron addition spectrum A+(k,omega) is obtained analytically for the one-dimensional (1D) supersymmetric t-J model with 1/r2 interaction. The result is obtained first for a small-sized system and its validity is checked against the numerical calculation. Then the general expression is found which is valid for arbitrary size of the system. The thermodynamic limit of A+(k,omega) has a simple analytic form with contributions from one spinon, one holon, and one antiholon-all of which obey fractional statistics. The upper edge of A+(k,omega) in the (k,omega) plane includes a delta-function peak which reduces to that of the single-electron band in the low-density limit.

Quantum Fluctuations of Chirality in One-Dimensional Spin-1/2 Multiferroics: Gapless Dielectric Response from Phasons and Chiral Solitons

We present a quantum theory for one-dimensional spin-1/2 multiferroics, where the vector spin chirality couples with the electric polarization. Based on exact diagonalization and bosonization, it is shown that quantum fluctuations appreciably reduce the chiral ordering amplitude and the associated ferroelectric polarization. This yields nearly collinear spin correlations in short-range scales, in qualitative agreement with recent neutron scattering experiments. There appear gapless chirality excitations described by phasons and new solitons, which can be experimentally verified from the low-energy dielectric response.We present a quantum theory for one-dimensional spin-1/2 multiferroics, where the vector spin chirality couples with the electric polarization. Based on exact diagonalization and bosonization, it is shown that quantum fluctuations appreciably reduce the chiral ordering amplitude and the associated ferroelectric polarization. This yields nearly collinear spin correlations in short-range scales, in qualitative agreement with recent neutron scattering experiments. There appear gapless chirality excitations described by phasons and new solitons, which can be experimentally verified from the low-energy dielectric response.

Charge Fluctuations and Superconductivity in an Extended Periodic Anderson Model: A Weak Coupling Theory

An extended periodic Anderson model, a model where repulsive interaction between an f -electron and a conduction electron is considered in addition to repulsive interaction between f -electrons, on a square lattice is studied with the fluctuation exchange approximation. It is found that charge susceptibilities at q =(π,π) are enhanced as the f -electron level e f becomes shallow, implying the tendency towards a charge density wave instability. The effective attractive interaction leading to superconductivity is then calculated, and is shown to depend on e f nonmonotonically.

Ground State of 3He Atoms in Narrow Tube

The ground state of 3 He atoms confined in a narrow tube is studied by the variational Monte Carlo method. It is found that 3 He atoms condense into a liquid state in the dilute limit in a certain ...

Exact dynamical structure factor of the degenerate Haldane-Shastry model

The dynamical structure factor S(q,omega) of the K-component ( K = 2, 3, 4) spin chain with a 1/r(2) interaction is derived exactly at zero temperature for the arbitrary size of the system. The result is interpreted in terms of a free quasiparticle picture which is a generalization of the spinon picture in the SU(2) case. The excited states consist of K quasiparticles each of which is characterized by a set of K-1 quantum numbers. Divergent singularities of S(q,omega) at the spectral edges are derived analytically. The analytic result is checked numerically for finite systems.

Exact charge dynamics in the supersymmetric t-J model with inverse-square interaction

The dynamical charge structure factor N ( Q ,ω) with Q smaller than the Fermi wave number is derived analytically for the one-dimensional supersymmetric t - J model with 1/ r 2 interaction. Strong spin-charge separation in dynamics is found. N ( Q ,ω) with a given electron density does not depend on the spin polarization of a system with an arbitrary size. In the thermodynamic limit, only two holons and one antiholon contribute to N ( Q ,ω). These results together with generalized ones for the SU( K ,1) supersymmetric t-J model are derived via solution of the Sutherland model in the strong coupling limit.

Exact spin dynamics of the 1/r2 supersymmetric t–J model in a magnetic field

The dynamical spin structure factor Szz(Q, ω) in the small momentum region is derived analytically for the one-dimensional supersymmetric t–J model with 1/r2 interaction. Strong spin–charge separation is found in the spin dynamics. The structure factor Szz(Q, ω) with a given spin polarization does not depend on electron density in the small momentum region. In the thermodynamic limit, only two spinons and one antispinon (magnon) contribute to Szz(Q, ω). These results are derived via solution of the SU(2,1) Sutherland model in the strong coupling limit.

Exact Dynamics of the SU(K) Haldane-Shastry Model.

The dynamical structure factor S ( q ,ω) of the S U ( K ) ( K =2,3,4) Haldane-Shastry model is derived exactly at zero temperature for arbitrary size of the system. The result is interpreted in terms of free quasi-particles which are generalization of spinons in the S U (2) case; the excited states relevant to S ( q ,ω) consist of K quasi-particles each of which is characterized by a set of K -1 quantum numbers. Near the boundaries of the region where S ( q ,ω) is nonzero, S ( q ,ω) shows the power-law singularity. It is found that the divergent singularity occurs only in the lowest edges starting from ( q ,ω) = (0,0) toward positive and negative q . The analytic result is checked numerically for finite systems via exact diagonalization and recursion methods.

Dynamical Properties of the One-Dimensional Supersymmetric t-J Model:A View from Elementary Excitations

Dynamical properties, such as dynamical spin and charge structure factors and single-particle spectral functions, are studied for the one-dimensional supersymmetric t - J model with inverse-square interaction. Exact diagonalization and the recursion method are used for finite systems up to 16 sites. A simple rule is proposed to understand the supermultiplet structure in the excitation spectrum. Numerical calculations show that the dynamical spin structure factor is independent of the electron density in the region where only two spinons contribute. In the electron removal spectrum from half-filling, close correspondence is found between the dominant contribution from three-spinon plus one-holon states in the t - J model and the two-spinon excitations in the Haldane-Shastry model. Comparison is made with dynamics of the nearest-neighbor supersymmetric t - J model.

Partially Solvable Anisotropic t-J Model with Long-Range Interactions

A new anisotropic t - J model in one dimension is proposed which has long-range hopping and exchange. This t - J model is only partially solvable in contrast to known integrable models with long-range interaction. In the high-density limit the model reduces to the XXZ chain with the long-range exchange. Some exact eigenfunctions are shown to be of the Jastrow type if certain conditions for an anisotropy parameter are satisfied. The ground state as well as the excitation spectrum for various values of the anisotropy parameter and filling are derived numerically. It is found that the Jastrow-type wave function is an excellent trial function for any value of the anisotropy parameter.