Takahiro Fukui

THERMODYNAMIC PROPERTIES OF HEISENBERG FERRIMAGNETIC SPIN CHAINS : FERROMAGNETIC-ANTIFERROMAGNETIC CROSSOVER

We study thermodynamic properties of the one-dimensional Heisenberg ferrimagnet with antiferromagnetically exchange-coupled spins of two kinds. The specific heat and the magnetic susceptibility are calculated employing a modified spin-wave theory as well as a quantum Monte Carlo method. The specific heat is proportional to

Combination of ferromagnetic and antiferromagnetic features in Heisenberg ferrimagnets

{T}^{1/2}

Characterization of ferrimagnetic Heisenberg chains according to the constituent spins

at low enough temperatures but shows a Schottky-like peak at mid temperatures. The susceptibility diverges as

ALTERNATING-SPIN LADDERS

{T}^{ensuremath{-}2}

Breakdown of the Mott insulator: Exact solution of an asymmetric Hubbard model

. We reveal that at low temperatures the model acts as a ferromagnet, while at mid temperatures it behaves like a gapped antiferromagnet.

Critical behavior of two-dimensional random hopping fermions with π-flux

We investigate the thermodynamic properties of Heisenberg ferrimagnetic mixed-spin chains both numerically and analytically with particular emphasis on the combination of ferromagnetic and antiferromagnetic features. Employing a new density-matrix renormalization-group technique as well as a quantum Monte Carlo method, we reveal the overall thermal behaviour: at very low temperatures, the specific heat and the magnetic susceptibility multiplied by the temperature behave like and , respectively, whereas at intermediate temperatures, they exhibit a Schottky-like peak and a minimum, respectively. Developing the modified spin-wave theory, we complement the numerical findings and give precise estimates for the low-temperature behaviour.

Anderson localization for two-dimensional random hopping model with SU(2) symmetry

Abstract:The low-energy structure and the thermodynamic properties of ferrimagnetic Heisenberg chains of alternating spins S and s are investigated by the use of numerical tools as well as the spin-wave theory. The elementary excitations are calculated through an efficient quantum Monte Carlo technique featuring imaginary-time correlation functions and are characterized in terms of interacting spin waves. The thermal behavior is analyzed with particular emphasis on its ferromagnetic and antiferromagnetic dual aspect. The extensive numerical and analytic calculations lead to the classification of the one-dimensional ferrimagnetic behavior according to the constituent spins: the ferromagnetic (S>2s), antiferromagnetic (S<2s), and balanced (S=2s) ferrimagnetism.

Development of Large Deformation in {sup 62}Cr

We investigate a two-leg spin-ladder system composed of alternating-spin chains with two different kinds of spins. The fixed-point properties are discussed by using spin-wave analysis and nonlinear sigma model techniques. The model contains various massive phases, reflecting the interplay between the bond alternation and the spin alternation.

Low-lying states in {sup 32}Mg studied by proton inelastic scattering

The breakdown of the Mott insulator is studied when the dissipative tunneling into the environment is introduced to the system. By exactly solving the one-dimensional asymmetric Hubbard model, we show how such a breakdown of the Mott insulator occurs. As the effect of the tunneling is increased, the Hubbard gap is monotonically decreased and finally disappears, resulting in the insulator-metal transition. We discuss the origin of this quantum-phase transition in comparison with other non-Hermitian systems recently studied.

Proton inelastic scattering on 32Mg

Abstract A two-dimensional random hopping model with N-species and π-flux is studied. The field theory at the band center is shown to be in the universality class of GL (4m, R )/ O (4m) non-linear sigma model. Vanishing beta function suggests delocalised states at the band center. Contrary to the similar universality class with broken time reversal symmetry, the present class is expected to have at least two fixed point. Large N-systems are shown to be in the weak-coupling fixed point, which is characterized by divergent density of state, while small N systems may be in the strong-coupling fixed point.