Impurity state in Haldane gap for S=1 Heisenberg antiferromagnetic chain with bond doping

Using a new impurity density matrix renormalization group scheme, we establish a reliable picture of how the low lying energy levels of a $S=1$ Heisenberg antiferromagnetic chain change {\it quantitatively} upon bond doping. A new impurity state gradually occurs in the Haldane gap as $J' < J$, while it appears only if $J'/J>\gamma_c$ with $1/\gamma_c=0.708$ as $J'>J$. The system is non-perturbative as $1\leq J'/J\leq\gamma_c$. This explains the appearance of a new state in the Haldane gap in a recent experiment on Y$_{2-x}$Ca$_x$BaNiO$_5$ [J.F. DiTusa, et al., Phys. Rev. Lett. 73 1857(1994)].Comment: 4 pages of uuencoded gzip'd postscrip

Electronic Raman scattering through a stripe ordering transition in La₂₋xSrxNiO₄

We describe the results of electronic Raman scattering experiments in two differently doped single crystals of La₂₋xSrxNiO₄ (x=0.225 and 1/3). In B₁g symmetry a crossover from weakly interacting to pseudogap-like behavior is observed at a charge-ordering temperature Tco. In B₂g symmetry a redistribution of electronic continua with decreasing temperature is accompanied by a loss of spectral weight below Tco in the low-frequency region due to opening of a pseudogap. The slope of the Raman response at vanishing frequencies is investigated, too. Its temperature behavior in B₂g symmetry, which predominantly selects charge carriers with momenta along the diagonals of the NiO₂ bonds, provides clear evidence for one-dimensional charge transport in the charge-ordered phase

Comparison of S=0 and S=1/2 Impurities in Haldane Chain Compound, Y2BaNiO5Y_{2}BaNiO_{5}

We present the effect of Zn (S=0) and Cu (S=1/2) substitution at the Ni site of S=1 Haldane chain compound $Y_{2}BaNiO_{5}$. $^{89}$Y NMR allows us to measure the local magnetic susceptibility at different distances from the defects. The $^{89}$Y NMR spectrum consists of one central peak and several less intense satellite peaks. The shift of the central peak measures the uniform susceptibility, which displays a Haldane gap $Delta$$equiv$100 K and it corresponds to an AF coupling J$equiv$260 K between the near-neighbor Ni spins. Zn or Cu substitution does not affect the Haldane gap. The satellites, which are evenly distributed on the two sides of the central peak, probe the antiferromagnetic staggered magnetization near the substituted site, which decays exponentially. Its extension is found identical for both impurities and corresponds accurately to the correlation length $xi$(T) determined by Monte Carlo (QMC) simulations for the pure compound. In the case of non-magnetic Zn, the temperature dependence of the induced magnetization is consistent with a Curie law with an "effective" spin S=0.4 on each side of Zn, which is well accounted by Quantum Monte Carlo computations of the spinless-defect-induced magnetism. In the case of magnetic Cu, the similarity of the induced magnetism to the Zn case implies a weak coupling of the Cu spin to the nearest- neighbor Ni spins. The slight reductionin the induced polarization with respect to Zn is reproduced by QMC computations by considering an antiferromagnetic coupling of strength J'=0.1-0.2 J between the S=1/2 Cu-spin and nearest-neighbor Ni-spin.Comment: 15 pages, 18 figures, submitted to Physical Review

Stoichiometry, structure, and properties of La{sub 2}NiO{sub 4+{delta}} and La{sub 2-x}Sr{sub x}NiO{sub 4{+-}{delta}}

The oxygen content phase diagram of La{sub 2}NiO{sub 4+{delta}} has been studied in detail using x-ray and neutron diffraction data from well-characterized specimens. There are numerous phase separations and phase transitions which are observed with changes in temperature and composition. The complexity of the phase diagram arises primarily from oxygen defect interactions, however the authors have also obtained evidence for coupled charge and spin ordering at {delta} = 0.125 corresponding to organization of holes into ordered domain walls. These domain walls act as antiphase boundaries between stripes of antiferromagnetically ordered nickel moments. Neutron scattering data on Sr-substituted compositions with well-defined oxygen content indicate incommensurate charge and spin correlations closely related to those in the x=0, {delta} = 0.125 composition. The incommensurability approaches 1/4 and the correlation length increases as the hole concentration approaches p = x+2{delta} = 0.25

Valor Nutritivo de Silagens de Híbridos de Sorgo (Sorghum bicolor (L.) Moench) sob Doses Crescentes de Adubação Nutritive Value of Five Sorghum Hybrids (Sorghum bicolor (L.) Moench) Silages under Increasing Fertilization Levels

Avaliou-se o valor nutritivo das silagens de cinco híbridos de sorgo (AG2002, AG2005E, AGX202, AGX213 e AGX215), cultivados sob doses crescentes de adubação (tratamento sem adubação, 0,5; 1,0; e 2,0 vezes a recomendação de adubação, consistindo de 0; 45,5; 91; e 182 kg/ha de N; 0; 49; 98; e 196 kg/ha de P2O5 ; e 0; 14; 28; e 56 kg/ha de K2O, além de 0; 42; 84; e 168 kg/ha de S, respectivamente, advindos da utilização de sulfato de amônio em cobertura), adotando-se o esquema fatorial 5x4 no delineamento em blocos casualizados, com quatro repetições. O plantio foi realizado no dia 06.11.1997, e as parcelas foram colhidas com os grãos no estádio farináceo. De cada parcela útil retirou-se uma amostra para enchimento dos silos experimentais, que, após 60 dias, foram abertos e amostrados novamente para se proceder à pré-secagem e às determinações do valor nutritivo (PB, fração fibrosa e DIVMS). Os dados foram interpretados por análise de variância e regressão, desdobrando-se a interação híbrido x adubo independentemente da sua significância. Os fatores qualitativos foram comparados, utilizando-se o teste de Tukey. Os modelos foram escolhidos, baseando-se na significância dos coeficientes de regressão, utilizando o teste de "t", Student, a 10% de probabilidade, e no coeficiente de determinação. O valor nutritivo das silagens diferiu entre os híbridos, observando-se maior valor nutritivo para a silagem do AG2005E, enquanto as silagens do AG2002 e do AGX213 apresentaram maior produção de nutrientes por unidade de área. O valor nutritivo das silagens foi afetado pelas doses de recomendação de adubação, embora de forma inconsistente<br>The nutritive value of five sorghum hybrids (AG-2002, AG-2005E, AG-X202, AG-X213 and AG-X215) silages, cultivated under increasing fertilization levels (control, 0.5, 1.0, and 2.0 times of the recommended fertilization, corresponding to 0, 45.5, 91, and 182 kg/ha N; 0, 49, 98, and 196 kg/ha de P2O5; and 0, 14, 28, and 56 kg/ha de K2O, besides of 0, 42, 84, and 168 kg/ha S, respectively, that came from the used ammonia sulfate). A complete randomized block design in a factorial 5x4 arrangement (five hybrids and four fertilization levels) with four replicates was used. The seeding time was at 11.06.1997 and plots were harvested at the soft dough stage of grain. From each plot, a sample was collected to fill up the experimental silos, which were opened after 60 days and sampled again to determine the pre drying weight and the nutritive value (CP, fiber fractions and IVDMD). Data were interpreted by means of analysis of variance and regression. The hybrid x fertilizer interaction was unrolled independently of its significance. The qualitative factor means were compared by Tukey test. The models were chosen based on regression coefficients significance, using Student "t" test, at 10% level, and on the determination coefficient. The silages nutritive value differed among the hybrids. AG2005E showed the highest nutritive value, whereas AG2002 and AGX213 showed the highest nutrient yield per unit of area. The fertilizers affected the silages nutritive value, but, inconsistentl