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We have performed magnetic susceptibility and high-field magnetization measurements on powder samples of Cu(DEP)Br2 (DEP=2,3-diethyl-pyrazine) and Cu(DMP)Cl2 (DMP=2,3-dimethyl-pyrazine) which are regarded as spin-1/2 two-leg spin-ladders in which the exchange constants are given by J ∥ along the leg and J ⊥ along the rung. The temperature dependences of magnetic susceptibilities of these compounds show a round peak at 11 and 18 K, respectively, and are compared with those calculated with a density matrix renormalization group method for α=J ∥/J ⊥=0.45–0.55. The exchange constants of the former and the latter compounds are evaluated to be \(J/k_{\rm B}=16.5~\mathrm{K}\) and \(J/k_{\rm B}=28.4~\mathrm{K}\), respectively. No magnetization at 1.3 K appears in magnetic fields of up to about 5 T for Cu(DEP)Br2 and about 14 T for Cu(DMP)Cl2, and then the magnetization increases monotonically to saturate at around 25 T and 38 T for respective compounds. Both magnetization curves are also compared with those calculated for α=0.45–0.55 using the same exchange parameter values as in the susceptibilities.

Results of electron spin resonance studies of copper pyrimidine dinitrate (Cu-PM, [PM-Cu(NO3)2(H2O)2] n , PM = pyrimidine), a spin-1/2 antiferromagnetic chain material with alternating g-tensor and Dzyaloshinskii-Moriya interactions, in pulsed magnetic fields up to 63 T are reported. The field-induced gap shows a non-monotonic behavior with a minimum in the vicinity of the saturation field H sat =48.5 T. This is associated with a transition from the sine-Gordon region to a spin-polarized state with magnon excitations. By comparing the entire set of experimental data with results of density matrix renormalization group calculations for Cu-PM, the validity of the used theoretical approach is proven.

We study the magnetization curve of the Heisenberg model on the quasi-one-dimensional kagome-strip lattice that shares the same lattice structure in the inner part with the two-dimensional kagome lattice. Our numerical calculations based on the density matrix renormalization group method reveal that the system shows several magnetization plateaus between zero magnetization and the saturated one; we find the presence of the magnetic plateaus with the n=7 height of the saturation for n =1,2,3,4,5 and 6 in the S =1/2 case, whereas we detect only the magnetic plateaus of n =1,3,5 and 6 in the S =1 case. In the cases of n =2,4 and 6 for the S=1/2 system, the Oshikawa-Yamanaka-Affleck condition suggests the occurrence of the translational symmetry breaking (TSB). We numerically confirm this non-trivial TSB in our results of local magnetizations. We have also found that the macroscopic jump appears near the saturation field irrespective of the spin amplitude as well as the two-dimensional kagome model., 6pages, 3figures, accepted for publication in Journal of Low Temperature Physics

The magnetization process of the S=1/2 three-leg spin tube with an asymmetric exchange interaction in each triangle unit is investigated by the numerical exact diagonalization and the density matrix renormalization group calculation. It is found that the 1/3 magnetization plateau appears due to two different mechanisms depending on the asymmetry. The phase diagrams of the 1/3 plateau is presented. In addition some cusp-like anomalies are found in the magnetization curve.

The effects of alternating magnetic field on the bipartite entanglement in an opened Ising chain are studied. Entropy is used to evaluate bipartite entanglement in the system. All-values entropy decreases with the strength of alternating field increases. The method of density matrix renormalization-group is applied to obtain logarithmic behavior of entropy. It is found that the logarithmic behavior with a central charge c does not vary with the length of the subsystem.

The variational self-energy method is applied to a study of the half-filled periodic Anderson model. Trial-self-energies and the numerical value of the Luttinger–Ward functional are obtained by diagonalization of a single c – f dimer. The dependence of the zero-temperature single-particle gap on the c – f-hybridization is found in qualitative agreement with mean-field theory for the Kondo-lattice, the specific heat agrees well with numerical results from density-matrix-renormalization group calculations. The single particle spectral function at finite-temperature shows marked deviations from a hybridization picture which agree well with quantum Monte–Carlo results.

We determine the bounday of the fully polarized ferromagnetic states in the one dimensional Kondo lattice model at partial conduction electron band filling by using a newly developed infinite size DMRG method which conserves the total spin quantum numbers. The obtained paramagnetic to ferromagnetic phase bounday is bellow J ≍ 3.5 for the whole range of band filling. By this we solve the controversy in the phase diagram over the extent of the ferromagnetic region close to half filling.

The authors study how magnetic and pairing correlation evolves with an increasing interchain hopping integral and decreasing dimerization of intrachain hopping integrals, by applying the density matrix renormalization group (DMRG) method to a three-chain extended Hubbard model at quarter filling for quasi-one-dimensional organic conductors, (TMTTF){sub 2}X and (TMTSF){sub 2}X. Magnetic correlation changes from weakly coupled chains of large-amplitude spin density waves to an interchain-coherence-developed spin density wave. Pairing correlation increases, though it still decays exponentially owing to a charge gap for parameters considered here.

The properties of the two-chain Hubbard Model doped away from half-filling are investigated using the density matrix renormalization group. A finite spin gap exists over a range of interchain hopping strength t⊥. A resonating valence bond ansatz provides an intuitive picture of the origin of the spin liquid phase.

The applicability of the multiplicative renormalization approach to onedimensional Fermi systems is further investigated. By extending the calculation to arbitrary energy variables it is proved that at least up to second order the reduced vertices and the Green's function do obey the renormalization group equations with renormalization factors independent of the energy variables. The Lie equations for the two-variable vertex are discussed. The vertices have been determined for special choices of the energy variables and agreement with the parquet diagram summation is obtained.