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The spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice (ATL) is an archetypal spin system hosting exotic quantum magnetism and dimensional crossover. However, the progress in experimental research on this field has been limited due to the scarcity of ideal model materials. Here, we show that rhenium oxyhalides $A_{3}$ReO$_{5}X_{2}$, where spin-1/2 Re$^{6+}$ ions form a layered structure of ATLs, allow for flexible chemical substitution in both cation $A^{2+}$ ($A$ = Ca, Sr, Ba, Pb) and anion $X^{-}$ ($X$ = Cl, Br) sites, leading to seven synthesizable compounds. By combining magnetic susceptibility and high-field magnetization measurements with theoretical calculations using the orthogonalized finite-temperature Lanczos method, we find that the anisotropy $J'/J$ ranges from 0.25 to 0.45 depending on the chemical composition. Our findings demonstrate that $A_{3}$ReO$_{5}X_{2}$ is an excellent platform for realizing diverse effective spin Hamiltonians that differ in the strength of the anisotropy $J'/J$ as well as the relevance of perturbation terms such as the Dzyaloshinskii-Moriya interaction and interlayer exchange coupling., Comment: 11 pages, 5 figures, SM: 4 pages, 2 figures

Exquisite sensitivities are a prominent advantage of quantum sensors. Ramsey sequences allow precise measurement of direct current fields, while Hahn-echo-like sequences measure alternating current fields. However, the latter are restrained for use with high-frequency fields (above approximately $1$ kHz) due to finite coherence times, leaving less-sensitive noncoherent methods for the low-frequency range. In this paper, we propose to bridge the gap with a fitting-based algorithm with a frequency-independent sensitivity to coherently measure low-frequency fields. As the algorithm benefits from coherence-based measurements, its demonstration with a single nitrogen-vacancy center gives a sensitivity of $9.4$ nT Hz$^{-0.5}$ for frequencies below about $0.6$ kHz down to near-constant fields. To inspect the potential in various scenarios, we apply the algorithm at a background field of tens of nTs, and we measure low-frequency signals via synchronization., Comment: 12 pages, 5 figures; supp 14 pages, 9 figures

The momentum correlation functions of S = -2 baryon pairs (p Xi^- and Lambda Lambda) produced in high-energy pp and pA collisions are investigated on the basis of the coupled-channel formalism. The strong interaction is described by the coupled-channel HAL QCD potential obtained by the lattice QCD simulations near physical quark masses, while the hadronic source function is taken to be a static Gaussian form. The coupled-channel effect, the threshold difference, the realistic strong interaction, and the Coulomb interaction are fully taken into account for the first time in the femtoscopic analysis of baryon-baryon correlations. The characteristic features of the experimental data for the p Xi^- and Lambda Lambda pairs at LHC are reproduced quantitatively with a suitable choice of non-femtoscopic parameters and the source size. The agreement between theory and experiment indicates that the N Xi (Lambda Lambda) interaction is moderately (weakly) attractive without having a quasi-bound (bound) state., Comment: 13 pages, 10 figures

The atomic masses of the isotopes $^{206,207}$Ra have been measured via decay-correlated mass spectroscopy using a multi-reflection time-of-flight mass spectrograph equipped with an $\alpha$-TOF detector. The Ra isotopes were produced as fusion-evaporation products in the $^{51}$V+$^{159}$Tb reaction system and delivered by the gas-filled recoil ion separator GARIS-II at RIKEN. The $\alpha$-TOF detector provides for high-accuracy mass measurements by correlating time-of-flight signals with subsequent $\alpha$-decay events. The masses of $^{206}$Ra and $^{207g,m}$Ra were directly measured using a multi-reflection time-of-flight mass spectrograph equipped with an $\alpha$-TOF detector. A mass excess of ME = 3538(15) keV/c$^2$ and an excitation energy of E$_{\rm ex}$ = 552(42) keV were determined. The $\alpha$-decay branching ratio of $^{207m}$Ra, b$\alpha$ = 0.26(20), was directly determined from decay-correlated time-of-flight signals, and the reduced alpha width of $^{207m}$Ra was calculated to be $\delta^2$ = 50+62-41 keV from the branching ratio. The spin-parity of $^{207m}$Ra was confirmed to be $J^\pi$ = 13/2$^-$ from decay correlated mass measurement results.

We present the first direct measurement of the atomic mass of a superheavy nuclide. Atoms of $^{257}$Db ($Z$=105) were produced online at the RIKEN Nishina Center for Accelerator-Based Science using the fusion-evaporation reaction $^{208}$Pb($^{51}$V, 2n)$^{257}$Db. The gas-filled recoil ion separator GARIS-II was used to suppress both the unreacted primary beam and some transfer products, prior to delivering the energetic beam of $^{257}$Db ions to a helium gas-filled ion stopping cell wherein they were thermalized. Thermalized $^{257}$Db$^{3+}$ ions were then transferred to a multi-reflection time-of-flight mass spectrograph for mass analysis. An alpha particle detector embedded in the ion time-of-flight detector allowed disambiguation of the rare $^{257}$Db$^{3+}$ time-of-flight detection events from background by means of correlation with characteristic $\alpha$-decays. The extreme sensitivity of this technique allowed a precision atomic mass determination from 11 events. The mass excess was determined to be $100\,063(231)_\textrm{stat}(132)_\textrm{sys}$~keV/c$^2$. Comparing to several mass models, we show the technique can be used to unambiguously determine the atomic number as $Z$=105 and should allow similar evaluations for heavier species in future work., Comment: Submitted to PRC as Rapid Comm., 5 pages, 4 figures

We present numerical results for finite-temperature $T>0$ thermodynamic quantities, entropy $s(T)$, uniform susceptibility $\chi_0(T)$ and the Wilson ratio $R(T)$, for several isotropic $S=1/2$ extended Heisenberg models which are prototype models for planar quantum spin liquids. We consider in this context the frustrated $J_1$-$J_2$ model on kagome, triangular, and square lattice, as well as the Heisenberg model on triangular lattice with the ring exchange. Our analysis reveals that typically in the spin-liquid parameter regimes the low-temperature $s(T)$ remains considerable, while $\chi_0(T)$ is reduced consistent mostly with a triplet gap. This leads to vanishing $R(T \to 0)$, being the indication of macroscopic number of singlets lying below triplet excitations. This is in contrast to $J_1$-$J_2$ Heisenberg chain, where $R(T \to 0)$ either remains finite in the gapless regime, or the singlet and triplet gap are equal in the dimerized regime.

We have developed a novel detector, referred to as an "$\alpha$-ToF detector", for correlated measurements of atomic masses and decay properties of low-yield, short-lived radioactive isotopes using a multi-reflection time-of-flight mass spectrograph. By correlating measured time-of-flight signals with decay events, it will be possible to suppress background events and obtain accurate, high-precision mass values even in cases of very low event rates. An offline test of the $\alpha$-ToF detector has shown that the time-of-flight detection efficiency for 5.48~MeV $\alpha$-rays is more than 90\% and yields a time resolution of 251.5(68)~ps and an energy resolution of 141.1(9)~keV. Using a two-dimensional spectrum of the correlated $\alpha$-ray energy and time-of-flight, the $\alpha$-rays from mixed $\alpha$ sources could be fairly well resolved., Comment: 6pages, 10 figures

The Quark-Meson-Coupling (QMC) model has been applied to the study of the properties of even-even super-heavy nuclei with 96 < Z < 110, over a wide range of neutron numbers. The aim is to identify the deformed shell gaps at N = 152 and N = 162 predicted in macroscopic-microscopic (macro-micro) models, in a model based on the mean-field Hartree-Fock+BCS approximation. The predictive power of the model has been tested on proton and neutron spherical shell gaps in light doubly closed (sub)shell nuclei. In the super-heavy region, the ground state binding energies of 98 < Z < 110 and 146 < N < 160 differ, in the majority of cases, from the measured values by less than 2.5 MeV, with the deviation decreasing with increasing Z and N. The axial quadrupole deformation parameter, calculated over the range of neutron numbers 138 < N < 184, revealed a prolate-oblate coexistence and shape transition around N = 168, followed by an oblate-spherical transition towards the expected N = 184 shell closure in Cm, Cf, Fm and No. The closure is not predicted in Rf, Sg, Hs and Ds as another shape transition to a highly deformed shape in Sg, Hs and Ds for N > 178 appears, while 288Rf (N = 184) remains oblate. The bulk properties predicted by QMC are found to have a limited sensitivity to the deformed shell gaps at N = 152 and 162. However, the evolution of the neutron single-particle spectra with 0 < beta2 < 0.55 gives unambiguous evidence for the location and size of the N = 152 and 162 gaps as a function of Z and N. In addition, the neutron number dependence of neutron pairing energies provides supporting evidence for existence of the energy gaps., Comment: 48 pages, 22 figures, 3 tables

Fragment mass distributions from fission of excited compound nucleus $^{178}$Pt have been deduced from the measured fragment velocities. The $^{178}$Pt nucleus was created at the JAEA tandem facility in a complete fusion reaction $^{36}$Ar + $^{142}$Nd, at beam energies of 155, 170 and 180 MeV. The data are indicative of a mixture of the mass-asymmetric and mass-symmetric fission modes associated with higher and lower total kinetic energies of the fragments, respectively. The measured fragment yields are dominated by asymmetric mass splits, with the symmetric mode contributing at the level of $\approx1/3$. This constitutes the first observation of a multimodal fission in the sub-lead region. Most probable experimental fragment-mass split of the asymmetric mode, $A_{L}/A_{H}\approx 79/99$, is well reproduced by nuclear density functional theory using the UNEDF1-HFB and D1S potentials. The symmetric mode is associated by theory with very elongated fission fragments, which is consistent with the observed total kinetic energy/fragment mass correlation., Comment: 6 pages, 4 figures

The masses of the exotic isotopes $^{210-214}$Ac and $^{210-214}$Ra have been measured with a multi-reflection time-of-flight mass spectrograph. These isotopes were obtained in flight as fusion-evaporation products behind the gas-filled recoil ion separator GARIS-II at RIKEN. The new direct mass measurements serve as an independent and direct benchmark for existing $\alpha$-$\gamma$ spectroscopy data in this mass region. Further, new mass anchor points are set for U and Np nuclei close to the $N=126$ shell closure for a future benchmark of the $Z=92$ sub-shell for neutron-deficient heavy isotopes. Our mass results are in general in good agreement with the previously indirectly-determined mass values. Together with the measurement data, reasons for possible mass ambiguities from decay-data links between ground states are discussed.

Spin-1/2 Heisenberg model on kagome lattice is a typical frustrated quantum spin system. A basic structure of kagome lattice is also present in kagome-strip lattice in one dimension, where a similar type of frustration is expected. We thus study the magnetization plateaus of the spin-1/2 Heisenberg model on a kagome-strip chain with three-independent antiferromagnetic exchange interactions by the density-matrix renormalization group method. In a certain range of exchange parameters, we find twelve kinds of magnetization plateaus, nine of which have magnetic structures breaking either translational or reflection symmetry spontaneously. The structures are classified by an array of five-site unit cells with specific bond-spin correlations. In a case with nontrivial plateau, 3/10 plateau, we find long-period magnetic structure with a period of four unit cells.

The masses of $^{246}$Es, $^{251}$Fm and the transfermium nuclei $^{249-252}$Md, and $^{254}$No, produced by hot- and cold-fusion reactions, in the vicinity of the deformed $N=152$ neutron shell closure, have been directly measured using a multireflection time-of-flight mass spectrograph. The masses of $^{246}$Es and $^{249,250,252}$Md were measured for the first time. Using the masses of $^{249,250}$Md as anchor points for $\alpha$ decay chains, the masses of heavier nuclei, up to $^{261}$Bh and $^{266}$Mt, were determined. These new masses were compared with theoretical global mass models and demonstrated to be in good agreement with macroscopic-microscopic models in this region. The empirical shell gap parameter $\delta_{2n}$ derived from three isotopic masses was updated with the new masses and corroborate the existence of the deformed $N=152$ neutron shell closure for Md and Lr.

K$_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ is a highly one-dimensional spin-1/2 inequilateral diamond-chain antiferromagnet. Spinon continuum and spin-singlet dimer excitations are observed in the inelastic neutron scattering spectra, which is in excellent agreement with a theoretical prediction: a dimer-monomer composite structure, where the dimer is caused by strong antiferromagnetic (AFM) coupling and the monomer forms an almost isolated quantum AFM chain controlling low-energy excitations. Moreover, muon spin rotation/relaxation spectroscopy shows no long-range ordering down to 90~mK, which is roughly three orders of magnitude lower than the exchange interaction of the quantum AFM chain. K$_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ is, thus, regarded as a compound that exhibits a Tomonaga-Luttinger spin liquid behavior at low temperatures close to the ground state.

Using a mulit-reflection time-of-flight mass spectrograph (MRTOF-MS) located after a gas cell coupled with the gas-filled recoil ion separator GARIS-II, the masses of several heavy nuclei have been directly and precisely measured. The nuclei were produced via fusion-evaporation reactions and separated from projectile-like and target-like particles using GARIS-II before being stopped in a helium-filled gas cell. Time-of-flight spectra for three isobar chains, 205Fr-205Rn-205At-205Po, 206Fr-206Rn-206At and 201Rn-201At-201Po-201Bi, were observed. Precision atomic mass values were determined for 205,206Fr, 201At, and 201Po., Comment: 5 pages, 2 figures

Exactly solvable frustrated quantum spin models consisting of a diamond unit structure are presented. The ground states are characterized by tetramer-dimer states with a macroscopic degeneracy in a certain range of isotropic exchange interaction. The lower bound of the excitation gap is exactly calculated to be finite and the bulk entropy in the limit of zero temperature remains finite depending on the shape of the boundary of system. Residual entropy is in a range of 0~6.1% of the entropy at high temperature for hexagonal diamond lattice and 0~8.4% for square diamond lattice. These diamond lattices are generalized to any dimensions and it is likely to be synthesized experimentally., Comment: 4 pages, 5 figures

A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ~15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from September to late November 2014, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ~350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy., Comment: 11 pages, 7 figures, 2 tables; accepted for publication in the Astrophysical Journal Letters; this version with small changes to affiliations

We discuss the exotic hadron structure and hadron-hadron interactions in view of heavy ion collisions. First, we demonstrate that a hadronic molecule with a large spatial size would be produced more abundantly in the coalescence model compared with the statistical model result. Secondly, we constrain the Lambda-Lambda interaction by using the recently measured Lambda-Lambda correlation data. We find that the RHIC-STAR data favor the Lambda-Lambda scattering parameters in the range 1/a_0 <= -0.8 fm^{-1} and r_{eff} >= 3 fm., Comment: 8 pages, 5 figures. Talk presented at the 11th International Conference on Hypernuclear and Strange Particle Physics (HYP2012), Oct.1-5, 2012, Barcelona, Spain

We apply the functional renormalization-group (FRG) equation to analyze the nature of the QCD critical point beyond the mean-field approximation by taking into consideration the fact that the soft mode associated with the QCD critical point is a linear combination of fluctuations of the chiral condensate and the quark-number density, rather than the pure chiral fluctuations. We first construct an extended quark-meson model in which a new field corresponding to quark-number density is introduced to the conventional one composed of the chiral fields sigma, pi and the quarks. The fluctuations of the quark-number density as well as the chiral condensate are taken into account by solving the FRG equation which contains sigma and the new field as coupled dynamical variables. It is found that the mixing of the two dynamical variables causes a kind of level repulsion between the curvature masses, which in turn leads to an expansion of the critical region of the QCD critical point, depending on the coupling constants in the model yet to be determined from microscopic theories or hopefully by experiments., Comment: 16 pages, 6 figures

Atacama Large Millimeter/submillimeter Array (ALMA) will be the world largest mm/submm interferometer, and currently the Early Science is ongoing, together with the commissioning and science verification (CSV). Here we present a study of the temporal phase stability of the entire ALMA system from antennas to the correlator. We verified the temporal phase stability of ALMA using data, taken during the last two years of CSV activities. The data consist of integrations on strong point sources (i.e., bright quasars) at various frequency bands, and at various baseline lengths (up to 600 m). From the observations of strong quasars for a long time (from a few tens of minutes, up to an hour), we derived the 2-point Allan Standard Deviation after the atmospheric phase correction using the 183 GHz Water Vapor Radiometer (WVR) installed in each 12 m antenna, and confirmed that the phase stability of all the baselines reached the ALMA specification. Since we applied the WVR phase correction to all the data mentioned above, we also studied the effectiveness of the WVR phase correction at various frequencies, baseline lengths, and weather conditions. The phase stability often improves a factor of 2 - 3 after the correction, and sometimes a factor of 7 improvement can be obtained. However, the corrected data still displays an increasing phase fluctuation as a function of baseline length, suggesting that the dry component (e.g., N2 and O2) in the atmosphere also contributes the phase fluctuation in the data, although the imperfection of the WVR phase correction cannot be ruled out at this moment., Comment: Proc. SPIE 8444-125, in press (7 pages, 4 figures, 1 table)

We employ a conformal mapping to explore the thermodynamics of strongly interacting matter at finite values of the baryon chemical potential $\mu$. This method allows us to identify the singularity corresponding to the critical point of a second-order phase transition at finite $\mu$, given information only at $\mu=0$. The scheme is potentially useful for computing thermodynamic properties of strongly interacting hot and dense matter in lattice gauge theory. The technique is illustrated by an application to a chiral effective model., Comment: 5 pages, 3 figures; published version

Determining ground states of correlated electron systems is fundamental to understanding novel phenomena in condensed matter physics. A difficulty, however, arises in a geometrically frustrated system in which the incompatibility between the global topology of an underlying lattice and local spin interactions gives rise to macroscopically degenerate ground states, potentially prompting the emergence of quantum spin states, such as resonating valence bond (RVB) and valence bond solid (VBS). Although theoretically proposed to exist in a kagome lattice -- one of the most highly frustrated lattices in two dimensions (2D) being comprised of corner-sharing triangles -- such quantum-fluctuation-induced states have not been observed experimentally. Here we report the first realization of the "pinwheel" VBS ground state in the S=1/2 deformed kagome lattice antiferromagnet Rb2Cu3SnF12. In this system, a lattice distortion breaks the translational symmetry of the ideal kagome lattice and stabilizes the VBS state., Comment: 10 pages, 4 figures and Supplemental Information

The formation of graphene on any desirable substrate is extremely essential for the successful replacement of Si with graphene in all technological applications in the beyond-CMOS era. Recently, we observed that a Ti layer formed on epitaxial graphene by electron-beam evaporation has the sufficiently large area of contact with the surface of epitaxial graphene for the exfoliation process to take place. We also observed that the exfoliated FLG on the Ti layer can be easily transferred onto a SiO2/Si substrate. In this paper, we have proposed a new technique for transferring graphene having a large area of several square mm from the graphitized vicinal SiC substrate. Raman scattering spectroscopy and low-energy electron microscopy analysis have revealed that we can transfer mono-layer and bi-layer graphene onto the SiO2/Si substrate by using the proposed transfer process. The initial size of epitaxial graphene formed on the SiC substrate is the only limitation of the new transfer process. The transfer process is expected to become an extremely important technology that will mark the beginning of a new era in the field of graphene electronics.

We report the crystal structure and unconventional magnetic ordering of Cs_2Cu_3CeF_{12}, which is composed of buckled kagome lattice of Cu^{2+} ions. The exchange network in the buckled kagome lattice is fairly anisotropic, so that the present spin system can be divided into two subsystems: alternating Heisenberg chains with strong antiferromagnetic exchange interactions and dangling spins. Although the direct exchange interactions between neighboring spins were found to be all antiferromagnetic, ferromagnetic magnetic ordering of the dangling spins was observed. Magnetization exhibits a plateau at one-third of the saturation magnetization. These observations can be understood in terms of the indirect interaction between dangling spins mediated by the chain spin., Comment: 4 pages, 3 figures

Decay properties of an isotope $^{266}$Bh and its daughter nucleus $^{262}$Db produced by the $^{248}$Cm($^{23}$Na, 5\textit{n}) reaction were studied by using a gas-filled recoil separator coupled with a position-sensitive semiconductor detector. $^{266}$Bh was clearly identified from the correlation of the known nuclide, $^{262}$Db. The obtained decay properties of $^{266}$Bh and $^{262}$Db are consistent with those observed in the $^{278}$113 chain, which provided further confirmation of the discovery of $^{278}$113., Comment: Accepted for publication in J. Phys. Soc. JPN., to be published in Vol.78 No. 6

Hexagonal antiferromagnets Cs$_2$Cu$_3$MF$_{12}$ (M = Zr, Hf and Sn) have uniform Kagome lattices of Cu$^{2+}$ with S = 1/2, whereas Rb$_2$Cu$_3$SnF$_{12}$ has a 2a by 2a enlarged cell as compared with the uniform Kagome lattice. The crystal data of Cs$_2$Cu$_3$SnF$_{12}$ synthesized first in the present work are reported. We performed magnetic susceptibility measurements on this family of Kagome antiferromagnet using single crystals. In the Cs$_2$Cu$_3$MF$_{12}$ systems, structural phase transitions were observed at $T_t = 225$ K, 172 K and 185 K for M = Zr, Hf and Sn, respectively. The magnetic susceptibilities observed for $T > T_t$ are almost perfectly described using theoretical results obtained by exact diagonalization for the 24-site Kagome cluster with $J/k_B = 244$ K, 266 K and 240 K, respectively. Magnetic ordering accompanied by the weak ferromagnetic moment occurs at $T_N = 23.5$ K, 24.5 K and 20.0 K, respectively. The origins of the weak ferromagnetic moment should be ascribed to the lattice distortion that breaks the hexagonal symmetry of the exchange network for $T < T_t$ and the Dzyaloshinsky-Moriya interaction. Rb$_2$Cu$_3$SnF$_{12}$ is magnetically described as a modified Kagome antiferromagnet with four types of neighboring exchange interaction. Neither structural nor magnetic phase transition was observed in Rb$_2$Cu$_3$SnF$_{12}$. Its magnetic ground state was found to be a spin singlet with a triplet gap. Using exact diagonalization for a 12-site Kagome cluster, we analyzed the magnetic susceptibility and evaluated individual exchange interactions. The causes leading to the different ground states in Cs$_2$Cu$_3$SnF$_{12}$ and Rb$_2$Cu$_3$SnF$_{12}$ are discussed., Comment: 12 pages, 9 figures. Submitted to Physical Review B. Errors on Fig. 7 were corrected

We synthesized single crystals of the new hexagonal compounds A$_2$Cu$_3$SnF$_{12}$ with A=Cs and Rb, and investigated their magnetic properties. These compounds are composed of Kagom\'{e} layers of corner-sharing CuF$_6$-octahedra. Cs$_2$Cu$_3$SnF$_{12}$ has the proper Kagom\'{e} layer at room temperature, and undergoes structural phase transition at $T_\mathrm{t}\simeq 185$ K. The temperature dependence of the magnetic susceptibility in Cs$_2$Cu$_3$SnF$_{12}$ agrees well with the result of the numerical calculation for $S=1/2$ two-dimensional Heisenberg Kagom\'{e} antiferromagnet down to $T_\mathrm{t}$ with the nearest exchange interaction $J/k_\mathrm{B}\simeq 240$ K. Although the magnetic susceptibility deviates from the calculated result below $T

We investigated the crystal structure of Rb$_2$Cu$_3$SnF$_{12}$ and its magnetic properties using single crystals. This compound is composed of Kagome layers of corner-sharing CuF$_{6}$ octahedra with a 2a x 2a enlarged cell as compared with the proper Kagome layer. Rb$_2$Cu$_3$SnF$_{12}$ is magnetically described as an $S$=1/2 modified Kagome antiferromagnet with four kinds of neighboring exchange interaction. From magnetic susceptibility and high-field magnetization measurements, it was found that the ground state is a disordered singlet with the spin gap, as predicted from a recent theory. Exact diagonalization for a 12-site Kagome cluster was performed to analyze the magnetic susceptibility, and individual exchange interactions were evaluated., Comment: 5 pages, 4 figures, To appear in J. Phys. Soc. Jpn. Vol. 77 No. 4

We performed 12CO(1-0), 13CO(1-0), and HCN(1-0) interferometric observations of the central region (about 450 pc in radius) of M82 with the Nobeyama Millimeter Array, and have successfully imaged a molecular superbubble and spurs. The center of the superbubble is clearly shifted from the nucleus by 140 pc. This position is close to that of the massive black hole (BH) of >460 Mo and the 2.2 micron secondary peak (a luminous supergiant dominated cluster), which strongly suggests that these objects may be related to the formation of the superbubble. Consideration of star formation in the cluster based on the infrared data indicates that (1) energy release from supernovae can account for the kinetic energy of the superbubble, (2) the total mass of stellar-mass BHs available for building-up the massive BH may be much higher than 460 Mo, and (3) it is possible to form the middle-mass BH of 100-1000 Mo within the timescale of the superbubble. We suggest that the massive BH was produced and is growing in the intense starburst region., Comment: 9 pages, 3 figures, to appear in ApJ Letter

We investigate pion source sizes through the Yano-Koonin-Podgoretski\u{\i} (YKP) parametrization for the Hanbury-Brown Twiss (HBT) effect in the CERN-SPS 158 GeV/A central collisions. We calculate two-particle correlation functions numerically based on a (3+1)-dimensional relativistic hydrodynamics with a first order phase transition and analyze the pair momentum dependence of the HBT radii extracted from the YKP parametrization in detail. We find that even in the case of a first order phase transition, expansion and the surface dominant freeze-out make the source in the hydrodynamical model opaque significantly. Consequently, the interpretation of the temporal radius parameter as the time duration becomes unavailable for the hydrodynamical model., Comment: 5 pages, LaTeX with six eps figures, Contribution to 'International Workshop XXVIII on Gross Properties of Nuclei And Nuclear Excitations'. Hirchegg, Austria, Jan 16-22, 2000

It is investigated, on the basis of the fluctuation exchange approximation, how the shape of the Fermi surface is modified in two-dimensional $t-t'-U$ Hubbard model at half filling as strength of the onsite Coulomb interaction $U$ is increased. The antiferromagnetic (AF) correlation length is shown to be enhanced as the Coulomb interaction get closer to the critical value $U_{\rm c}$ for the onset AF order. At the same time, the shape of the renormalized Fermi surface is deformed showing the tendency of nesting near $U_{\rm c}$., Comment: 2 pages