Mitsuhiro Arikawa

Spin Nematic Phase in S=1 Triangular Antiferromagnets

Spin nematic order is investigated for an S =1 spin model on a triangular lattice with bilinear–biquadratic interactions. We particularly studied an antiferro nematic order phase with a three-sublattice structure, and magnetic properties are calculated at zero temperature by bosonization. Two types of bosonic excitations are found and we calculated dynamic and static spin correlations. One is a gapless excitation with linear energy dispersion around k ∼ 0 , and this leads to a finite spin susceptibility at T =0 and would have a specific heat C ( T ) ∼ T 2 at low temperatures. These behaviors can explain many of the characteristic features of a recently discovered spin liquid state in the triangular magnet, NiGa 2 S 4 .

Low-lying excitations of the three-leg spin tube: A density-matrix renormalization group study

Using the (dynamical) density-matrix renormalization group method, we study the low-energy physics of three-leg antiferromagnetic Heisenberg model where the periodic boundary conditions are applied in the rung direction. We confirm that the spin excitations are always gapped as long as the intraring couplings form a regular triangle. From precise finite-size-scaling analyses of the spin gap and dimerization order parameter, we also find that the spin gap is collapsed by very small asymmetric modulation of the intraring couplings. Moreover, the dynamical spin structure factors on the intraleg and interleg correlations are calculated. It is demonstrated that the low-lying structure of the interleg spectra is particularly affected by the asymmetric modulation.

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.

Edge states in graphene in magnetic fields : A specialty of the edge mode embedded in the n=0 Landau band

While usual edge states in the quantum Hall effect (QHE) reside between adjacent Landau levels, QHE in graphene has a peculiar edge mode at

Edge states of a spin-(1/2) two-leg ladder with four-spin ring exchange

E=0

The spin nematic state in triangular antiferromagnets

that resides right within the

Spinon Excitations in the XX Chain: Spectra, Transition Rates, Observability

n=0

Exact dynamical structure factor of the degenerate Haldane-Shastry model

Landau level as protected by the chiral symmetry. We have theoretically studied the edge states to show that the

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

E=0

Elementary Excitations and Dynamical Correlation Functions of the Calogero-Sutherland Model with Internal Symmetry

edge mode, despite being embedded in the bulk Landau level, does give rise to a wave function whose charge is accumulated along zigzag edges. This property, totally outside continuum models, implies that the graphene QHE harbors edges distinct from ordinary QHE edges with their topological origin. In the charge accumulation the bulk states redistribute their charge significantly, which may be called a topological compensation of charge density. The real-space behavior obtained here should be observable in a scanning tunnel microscope imaging.