Quasiperiodic Hubbard chains

Low energy properties of half-filled Fibonacci Hubbard models are studied by weak coupling renormalization group and density matrix renormalization group method. In the case of diagonal modulation, weak Coulomb repulsion is irrelevant and the system behaves as a free Fibonacci chain, while for strong Coulomb repulsion, the charge sector is a Mott insulator and the spin sector behaves as a uniform Heisenberg antiferromagnetic chain. The off-diagonal modulation always drives the charge sector to a Mott insulator and the spin sector to a Fibonacci antiferromagnetic Heisenberg chain.Comment: 4 pages, 4 figures; Final version to appear in Phys. Rev. Let

Magnetization plateaus in antiferromagnetic-(ferromagnetic)_{n} polymerized S=1/2 XXZ chains

The plateau-non-plateau transition in the antiferromagnetic-(ferromagnetic)$_{n}$ polymerized $S=1/2$ XXZ chains under the magnetic field is investigated. The universality class of this transition belongs to the Brezinskii-Kosterlitz-Thouless (BKT) type. The critical points are determined by level spectroscopy analysis of the numerical diagonalization data for $4 \leq p \leq 13$ where $p(\equiv n+1)$ is the size of a unit cell. It is found that the critical strength of ferromagnetic coupling decreases with $p$ for small $p$ but increases for larger enough $p$. It is also found that the plateau for large $p$ is wide enough for moderate values of exchange coupling so that it should be easily observed experimentally. This is in contrast to the plateaus for $p = 3$ chains which are narrow for a wide range of exchange coupling even away from the critical point

Density Matrix Renormalization Group Study of the Haldane Phase in Random One-Dimensional Antiferromagnets

It is conjectured that the Haldane phase of the S=1 antiferromagnetic Heisenberg chain and the $S=1/2$ ferromagnetic-antiferromagnetic alternating Heisenberg chain is stable against any strength of randomness, because of imposed breakdown of translational symmetry. This conjecture is confirmed by the density matrix renormalization group calculation of the string order parameter and the energy gap distribution.Comment: 4 Pages, 7 figures; Considerable revisions are made in abstract and main text. Final accepted versio

EXAFS Study on Local Structure of Iron Crystal by the Use of Asymmetrical Monochromator and PSPC

The EXAFS spectroscopy equipment constructed from an asymmetrical cut flat monochromator and PSPC is applied to the structural determination of pure α-iron which has small difference (0.038nm) in the first and second nearest neighbour distance. The efficiency of the curve fitting method for the two shell model of known structure material (α-iron) is discussed, in addition to describing the details of the experimental procedure of our new type of spectrometer and of the EXAFS data analysis

Interacting Boson Theory of the Magnetization Process of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain

The low temperature magnetization process of the ferromagnetic-antiferromagnetic Heisenberg chain is studied using the interacting boson approximation. In the low field regime and near the saturation field, the spin wave excitations are approximated by the $\delta$ function boson gas for which the Bethe ansatz solution is available. The finite temperature properties are calculated by solving the integral equation numerically. The comparison is made with Monte Carlo calculation and the limit of the applicability of the present approximation is discussed.Comment: 4 pages, 7 figure

The antiferromagnetic order in an F-AF random alternating quantum spin chain : (CH_3)_2 CHNH_3 Cu(Cl_x Br_{1-x})_3

A possibility of the uniform antiferromagnetic order is pointed out in an S=1/2 ferromagnetic (F) - antiferromagnetic (AF) random alternating Heisenberg quantum spin chain compound: (CH_3)_2 CHNH_3 Cu(Cl_x Br_{1-x})_3. The system possesses the bond alternation of strong random bonds that take +/- 2J and weak uniform AF bonds of -J. In the pure concentration limits, the model reduces to the AF-AF alternation chain at x=0 and to the F-AF alternation chain at x=1. The nonequilibrium relaxation of large-scale quantum Monte Carlo simulations exhibits critical behaviors of the uniform AF order in the intermediate concentration region, which explains the experimental observation of the magnetic phase transition. The present results suggest that the uniform AF order may survive even in the presence of the randomly located ferromagnetic bonds.Comment: 4 pages, 3 figure

Pelatihan terhadap Keterampilan Kader Posyandu

Permasalahan yang diteliti adalah adakah perbedaan keterampilan kader posyandu dalam pengukuran antropometri sebelum dan sesudah pelatihan. Tujuan penelitian ini adalah untuk mengetahui perbedaan keterampilan kader posyandu dalam pengukuran antropometri sebelum dan sesudah pelatihan di wilayah kerja Puskesmas Tarub, Kabupaten Tegal. Metode penelitian menggunakan eksperimen semu dengan rancangan one group pre dan post test design. Sampel berjumlah 25 kader posyandu. Variabel yang diteliti yaitu keterampilan kader sebelum dan sesudah intervensi. Skor keterampilan diukur dua kali yaitu pretest dan posttest. Hasil penelitian menunjukkan dengan uji wilcoxon diperoleh nilai p= 0,0001. Nilai (p<0,05) berarti ada perbedaan yang bermakna dari nilai keterampilan pada saat pretest dan posttest. Hal ini berarti menunjukkan ada perbedaan keterampilan kader posyandu dalam pengukuran antropometri sebelum dan sesudah pelatihan di wilayah kerja Puskesmas Tarub, Kabupaten Tegal. Simpulan penelitian adalah ada perbedaan keterampilan kader posyandu dalam pengukuran antropometri sebelum dan sesudah pelatihan.Research problem was diference of skill posyandu cadres in anthropometric measurements before and after training. Purpose of this study was to determine diferences in skill posyandu cadres in anthropometric measurement before and after training in the working area Tarub Health Center, Tegal District. Research method used quasi-experimental design with one group pre and post test design. Samples were amount of 25 cadres. Variable studied was the skills of cadres before and after training. Scores skills measured by twice pretest and posttest. Test statistic obtained by Wilcoxon test was p value=0,0001. It showed the value <0,05 then there was a significant difference from the values of skills at pretest and posttest. There was difference in skills of posyandu cadres on anthropometric measurement before and after training in the working area Tarub Health Center, Tegal district. Conclusion, there was difference in skills of posyandu cadres on anthropometric measurements before and after training

Quantum Monte Carlo Study on Magnetization Processes

A quantum Monte Carlo method combining update of the loop algorithm with the global flip of the world line is proposed as an efficient method to study the magnetization process in an external field, which has been difficult because of inefficiency of the update of the total magnetization. The method is demonstrated in the one dimensional antiferromagnetic Heisenberg model and the trimer model. We attempted various other Monte Carlo algorithms to study systems in the external field and compared their efficiency.Comment: 5 pages, 9 figures; added references for section 1, corrected typo

Critical Properties of the transition between the Haldane phase and the large-D phase of the spin-1/2 ferromagnetic-antiferromagnetic Heisenberg chain with on-site anisotropy"

We analytically study the ground-state quantum phase transition between the Haldane phase and the large-$D$ (LD) phase of the $S=1/2$ ferromagnetic-antiferromagnetic alternating Heisenberg chain with on-site anisotropy. We transform this model into a generalized version of the alternating antiferromagnetic Heisenberg model with anisotropy. In the transformed model, the competition between the transverse and longitudinal bond alternations yields the Haldane-LD transition. Using the bosonization method, we show that the critical exponents vary continuously on the Haldane-LD boundary. Our scaling relations between critical exponents very well explains the numerical results by Hida.Comment: text 12 pages (Plain TeX), LaTeX sourse files of a table and a figure on reques

Quantum Antiferromagnetism in Quasicrystals

The antiferromagnetic Heisenberg model is studied on a two-dimensional bipartite quasiperiodic lattice. The distribution of local staggered magnetic moments is determined on finite square approximants with up to 1393 sites, using the Stochastic Series Expansion Quantum Monte Carlo method. A non-trivial inhomogeneous ground state is found. For a given local coordination number, the values of the magnetic moments are spread out, reflecting the fact that no two sites in a quasicrystal are identical. A hierarchical structure in the values of the moments is observed which arises from the self-similarity of the quasiperiodic lattice. Furthermore, the computed spin structure factor shows antiferromagnetic modulations that can be measured in neutron scattering and nuclear magnetic resonance experiments. This generic model is a first step towards understanding magnetic quasicrystals such as the recently discovered Zn-Mg-Ho icosahedral structure.Comment: RevTex, 4 pages with 5 figure