The structure of $^{19,20,22}$C has been investigated using high-energy (about 240 MeV/nucleon) one- and two-neutron removal reactions on a carbon target. Measurements were made of the inclusive cross sections and momentum distributions for the charg
ed residues. Narrow momentum distributions were observed for one-neutron removal from $^{19}$C and $^{20}$C and two-neutron removal from $^{22}$C. Two-neutron removal from $^{20}$C resulted in a relatively broad momentum distribution. The results are compared with eikonal-model calculations combined with shell-model structure information. The neutron-removal cross sections and associated momentum distributions are calculated for transitions to both the particle-bound and particle-unbound final states. The calculations take into account the population of the mass $A-1$ reaction residues, $^{A-1}$C, and, following one-neutron emission after one-neutron removal, the mass $A-2$ two-neutron removal residues, $^{A-2}$C. The smaller contributions of direct two-neutron removal, that populate the $^{A-2}$C residues in a single step, are also computed. The data and calculations are shown to be in good overall agreement and consistent with the predicted shell-model ground state configurations and the one-neutron overlaps with low-lying states in $^{18-21}$C. These suggest significant $ u{s}_{1/2}^2$ valence neutron configurations in both $^{20}$C and $^{22}$C. The results for $^{22}$C strongly support the picture of $^{22}$C as a two-neutron halo nucleus with a dominant $ u{s}_{1/2}^2$ ground state configuration.
We study the three-dimensional bosonic t-J model, i.e., the t-J model of bosonic electrons, at finite temperatures. This model describes the $s={1 over 2}$ Heisenberg spin model with the anisotropic exchange coupling $J_{bot}=-alpha J_z$ and doped {i
t bosonic} holes, which is an effective system of the Bose-Hubbard model with strong repulsions. The bosonic electron operator $B_{rsigma}$ at the site $r$ with a two-component (pseudo-)spin $sigma (=1,2)$ is treated as a hard-core boson operator, and represented by a composite of two slave particles; a spinon described by a Schwinger boson (CP$^1$ boson) $z_{rsigma}$ and a holon described by a hard-core-boson field $phi_r$ as $B_{rsigma}=phi^dag_r z_{rsigma}$. By means of Monte Carlo simulations, we study its finite-temperature phase structure including the $alpha$ dependence, the possible phenomena like appearance of checkerboard long-range order, super-counterflow, superfluid, and phase separation, etc. The obtained results may be taken as predictions about experiments of two-component cold bosonic atoms in the cubic optical lattice.
The magnetic field effect on the phase diagram of the organic Mott system $kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br in which the bandwidth was tuned by the substitution of deuterated molecules was studied by means of the resistivity measurements perf
ormed in magnetic fields. The lower critical point of the first-order Mott transition, which ended on the upper critical field $H_{rm c2}$-temperature plane of the superconductivity, was determined experimentally in addition to the previously observed upper critical end point. The lower critical end point moved to a lower temperature with the suppression of $T_{rm c}$ in magnetic fields and the Mott transition recognized so far as the $S$-shaped curve reached $T =$ 0 when $H > H_{rm c2}$ in the end.
In order to reveal the stellar mass distribution of z~3 galaxies, we are conducting deep imaging observations of U-dropout Lyman Break Galaxies (LBGs) with Adaptive Optics (AO) systems in K-band, which corresponds to rest-frame V-band of z~3 galaxies
. The results of the Subaru intensive-program observations with AO36/NGS/IRCS indicate that 1) the K-band peaks of some of the LBGs brighter than K=22.0 mag show significant offset from those in the optical images, 2) the z~3 Mv* LBGs and serendipitously observed Distant Red Galaxies (DRGs) have flat profiles similar to disk galaxies in the local universe (i.e., Sersic with n<2), and 3) the surface stellar mass densities of the Mv* LBGs are 3-6 times larger than those of disk galaxies at z=0-1. Considering the lack of n>2 systems among the luminous z~3 LBGs and DRGs, and their strong spatial clustering, we infer that the dense n<2 disk-like structures evolve into the n>2 spheroids of nearby galaxies through relaxations due to major merger events.
