Spin-Reorientation Transition of Field-Induced Magnetic Ordering Phases in the Anisotropic Haldane System

A possible spin-reorientation transition in field-induced magnetic ordering phases of the S=1 Haldane system with large easy-plane anisotropy is proposed, using an effective Lagrangian formalism as well as the density matrix renormalization group method. Such a spin-reorientation transition is predicted in the case where the applied magnetic field is inclined from the easy axis of the anisotropy. We point out that this transition has a close connection with a variation of the order parameter even at zero temperature, although it is different from a quantum analog of the so-called spin-flop transition proposed for the system having a strong easy axis anisotropy. In connection with a novel phase observed recently in the Haldane system at high fields, we discuss possible implications for the field-induced magnetic ordering.Comment: 14 pages, 7 figure

Field induced long-range-ordering in an S=1 quasi-one-dimensional Heisenberg antiferromagnet

We have measured the heat capacity and magnetization of the spin one one-dimensional Heisenberg antiferromagnet NDMAP and constructed a magnetic field versus temperature phase diagram. We found a field induced long-range magnetic ordering. We have been successful in explaining the phase diagram theoretically.Comment: 6 pages, 18 figure

Third Neighbor Correlators of Spin-1/2 Heisenberg Antiferromagnet

We exactly evaluate the third neighbor correlator and all the possible non-zero correlators <S^{alpha}_j S^{beta}_{j+1} S^{gamma}_{j+2} S^{delta}_{j+3}> of the spin-1/2 Heisenberg $XXX$ antiferromagnet in the ground state without magnetic field. All the correlators are expressed in terms of certain combinations of logarithm ln2, the Riemann zeta function zeta(3), zeta(5) with rational coefficients. The results accurately coincide with the numerical ones obtained by the density-matrix renormalization group method and the numerical diagonalization.Comment: 4 page

SU(2)/Z2SU(2)/Z_2 symmetry of the BKT transition and twisted boundary conditio n

Berezinskii-Kosterlitz-Thouless (BKT) transition, the transition of the 2D sine-Gordon model, plays an important role in the low dimensional physics. We relate the operator content of the BKT transition to that of the SU(2) Wess-Zumino-Witten model, using twisted boundary conditions. With this method, in order to determine the BKT critical point, we can use the level crossing of the lower excitations than the periodic boundary case, thus the convergence to the transition point is highly improved. Then we verify the efficiency of this method by applying to the S=1,2 spin chains.Comment: LaTex2e,, 33 pages, 14 figures in eps file

Experimental Evidence of a Haldane Gap in an S = 2 Quasi-linear Chain Antiferromagnet

The magnetic susceptibility of the $S = 2$ quasi-linear chain Heisenberg antiferromagnet (2,$2'$-bipyridine)trichloromanganese(III), MnCl_{3}(bipy), has been measured from 1.8 to 300 K with the magnetic field, H, parallel and perpendicular to the chains. The analyzed data yield $g\approx 2$ and $J\approx 35$ K. The magnetization, M, has been studied at 30 mK and 1.4 K in H up to 16 T. No evidence of long-range order is observed. Depending on crystal orientation, $M\approx 0$ at 30 mK until a critical field is achieved ($H_{c\|} = 1.2\pm 0.2 T$ and $H_{c\bot} = 1.8\pm 0.2 T), where M increases continuously as H is increased. These results are interpreted as evidence of a Haldane gap.Comment: 11 pages, 4 figure

Behavior of a frustrated quantum spin chain with bond dimerization

We clarified behavior of the excitation gap in a frustrated S=1/2 quantum spin chain with bond dimerization by using the numerical diagonalization of finite systems and a variational approach. The model interpolates between the independent dimer model and the S=1 spin chain by changing a strength of the dimerization. The energy gap is minimum at the fully-frustrated point, where a localized kink and a freely mobile anti-kink govern the low-lying excitations. Away from the point, a kink and an antikink form a bound state by an effective triangular potential between them. The consequential gap enhancement and the localization length of the bound state is obtained exactly in the continuous limit. The gap enhancement obeys a power law with exponent 2/3. The method and the obtained results are common to other frustrated double spin-chain systems, such as the one-dimensional J_1 - J_2 model, or the frustrated ladder model.Comment: 11 pages, REVTeX, 8 figures in eps-fil

Magnetic Field Effect on Crossover Temperature from Non-Fermi Liquid to Fermi Liquid Behavior in f^2-Impurity Systems with Crystalline-Electric-Field Singlet State Competing with Kondo-Yosida Singlet State

We investigate the magnetic field dependence of the physical properties of f^2-configuration systems with a crystalline-electric field (CEF) singlet ground state, which gives rise to a non- Fermi liquid (NFL) fixed point due to the competition between the Kondo-Yosida singlet and CEF singlet states. On the basis of the numerical renormalization group method, we find that the magnetic field breaks this NFL fixed point via two mechanisms: one causing the polarization of f-electrons and the other giving the "channel" anisotropy. These two mechanisms induce a difference in the magnetic field dependence of the characteristic temperature T_F^{*}(H), the crossover temperature from NFL to Fermi-liquid behavior. While the polarization of f-electrons gives T_F^{*}(H) \propto H^x (x\sim2.0), the "channel" anisotropy gives the H-independent T_F^{*}(H). These two mechanisms cross over continuously at approximately the crossover magnetic field H_c, where an anomalous H-dependence of T_F^{*}(H) appears. Such T_F^{*}(H) well reproduces the NFL behaviors observed in Th_{1-x}U_xRu_2Si_2. We also find that the H-dependence of the resistivity and the magnetic susceptibility are in good agreement with the experimental results of this material. These results suggest that the NFL behaviors observed in Th_{1-x}U_xRu_2Si_2 can be understood if this material is located in the CEF singlet side near the critical phase boundary between the two singlet states.Comment: 8 pages, 8figure

Absence of string order in the anisotropic S=2 Heisenberg antiferromagnet

We study an AFM Heisenberg S=2 quantum spin chain at T=0 with both interaction and on-site anisotropy, H = \sum_{i} {1/2}(S^{+}_{i}S^{-}_{i+1}+S^{-}_{i}S^{+}_{i+1}) +J^{z}S^{z}_{i}S^{z}_{i+1}+D(S^{z}_{i})^{2}. Contradictory scenarios exist for the S=2 anisotropic phase diagram, implying different mechanisms of the emergence of the classical limit. One main AKLT-based scenario predicts the emergence of a cascade of phase transitions not seen in the S=1 case. Another scenario is in favor of an almost classical phase diagram for S=2; the S=1 case then is very special with its dominant quantum effects. Numerical studies have not been conclusive. Using the DMRG, the existence of hidden topological order in the anisotropic S=2 chain is examined, as it distinguishes between the proposed scenarios. We show that the topological order is zero in the thermodynamical limit in all disordered phases, in particular in the new phase interposed between the Haldane and large-$D$ phases. This excludes the AKLT-model based scenario in favor of an almost classical phase diagram for the $S\leq 2$ spin chains.Comment: 9 pages, 9 eps figures, uses RevTeX, submitted to PR

The Calibration of Monochromatic Far-Infrared Star Formation Rate Indicators

(Abridged) Spitzer data at 24, 70, and 160 micron and ground-based H-alpha images are analyzed for a sample of 189 nearby star-forming and starburst galaxies to investigate whether reliable star formation rate (SFR) indicators can be defined using the monochromatic infrared dust emission centered at 70 and 160 micron. We compare recently published recipes for SFR measures using combinations of the 24 micron and observed H-alpha luminosities with those using 24 micron luminosity alone. From these comparisons, we derive a reference SFR indicator for use in our analysis. Linear correlations between SFR and the 70 and 160 micron luminosity are found for L(70)>=1.4x10^{42} erg/s and L(160)>=2x10^{42} erg/s, corresponding to SFR>=0.1-0.3 M_sun/yr. Below those two luminosity limits, the relation between SFR and 70 micron (160 micron) luminosity is non-linear and SFR calibrations become problematic. The dispersion of the data around the mean trend increases for increasing wavelength, becoming about 25% (factor ~2) larger at 70 (160) micron than at 24 micron. The increasing dispersion is likely an effect of the increasing contribution to the infrared emission of dust heated by stellar populations not associated with the current star formation. The non-linear relation between SFR and the 70 and 160 micron emission at faint galaxy luminosities suggests that the increasing transparency of the interstellar medium, decreasing effective dust temperature, and decreasing filling factor of star forming regions across the galaxy become important factors for decreasing luminosity. The SFR calibrations are provided for galaxies with oxygen abundance 12+Log(O/H)>8.1. At lower metallicity the infrared luminosity no longer reliably traces the SFR because galaxies are less dusty and more transparent.Comment: 69 pages, 19 figures, 2 tables; accepted for publication on Ap

High testosterone levels in prostate tissue obtained by needle biopsy correlate with poor-prognosis factors in prostate cancer patients

Background: There is currently no consensus on the correlations between androgen concentrations in prostate tissue and blood and stage and pathological grade of prostate cancer. In this study, we used a newly-developed ultra-sensitive liquid-chromatography tandem mass spectrometry method to measure testosterone (T) and dihydrotestosterone (DHT) concentrations in blood and needle biopsy prostate specimens from patients with prostate cancer.Methods: We analyzed androgen levels in 196 men diagnosed with prostate cancer. All patients had undergone systematic needle biopsy, and an additional needle biopsy from the peripheral zone was conducted for the simultaneous determination of T and DHT. We analyzed the relationships between T and DHT levels in tissue and blood and Gleason score, clinical stage, and percentage of positive biopsy cores, using multivariate analysis. Results: The median T and DHT levels in blood were 3551.0 pg/mL and 330.5 pg/mL, respectively. There was a strong correlation between serum T and DHT. The median T and DHT levels in prostate tissue were 0.5667 pg/mg and 7.0625 pg/mg, respectively. In multivariate analysis, serum prostate-specific antigen and tissue T levels were significantly associated with poor prognosis; high T levels in prostate tissue were significantly related to high Gleason score (p = 0.041), advanced clinical stage (p = 0.002), and a high percentage of positive biopsy cores (p = 0.001). Conclusions: The results of this study indicate that high T levels in prostate tissue are related to high Gleason score, advanced clinical stage, and a high percentage of positive biopsy cores in patients with prostate cancer. T level in needle biopsy specimens may therefore be a useful prognostic factor in prostate cancer patients