Strong coupling theory of the spinless charges on the triangular lattices: possibility of a new quantum liquid

We propose a new type of charge liquid state in the spinless fermion system on a triangular lattice under strong inter-site Coulomb interactions, $V$. In the strong coupling limit ($t=0$), the ground state is classical and disordered due to geometrical frustration. The introduction of small t will drive the system to a partially ordered phase which we call a "pinball liquid". A possibly long range ordered Wigner crystal solid coexist with a liquid component which are moving around them like a pinball. This liquid is dominant over wide range of filling, even away from the regular triangle, and is also realized in the hard core boson systems. Relevance to the organic theta-ET_2X is discsussed.Comment: 4pages, 7figure

Spin Dynamics of Double-Exchange Manganites with Magnetic Frustration

This work examines the effects of magnetic frustration due to competing ferromagnetic and antiferromagnetic Heisenberg interactions on the spin dynamics of the double-exchange model. When the local moments are non-colinear, a charge-density wave forms because the electrons prefer to sit on lines of sites that are coupled ferromagnetically. With increasing hopping energy, the local spins become aligned and the average spin-wave stiffness increases. Phase separation is found only within a narrow range of hopping energies. Results of this work are applied to the field-induced jump in the spin-wave stiffness observed in the manganite Pr$_{1-x}$Ca$_x$MnO$_3$ with $0.3 \le x \le 0.4$.Comment: 10 pages, 3 figure

Ferroelectricity induced by spin-dependent metal-ligand hybridization in Ba2_2CoGe2_2O7_7

We have investigated the variation of induced ferroelectric polarization under magnetic field with various directions and magnitudes in a staggered antiferromagnet Ba$_2$CoGe$_2$O$_7$. While the ferroelectric polarization cannot be explained by the well-accepted spin current model nor exchange striction mechanism, we have shown that it is induced by the spin-dependent $p$-$d$ hybridization between the transition-metal (Co) and ligand (O) via the spin-orbit interaction. On the basis of the correspondence between the direction of electric polarization and the magnetic state, we have also demonstrated the electrical control of the magnetization direction.Comment: 4 pages, 4 figure

Quantum Monte Carlo study of the transverse-field Ising model on a frustrated checkerboard lattice

We present the numerical results for low temperature behavior of the transverse-field Ising model on a frustrated checkerboard lattice, with focus on the effect of both quantum and thermal fluctuations. Applying the recently-developed continuous-time quantum Monte Carlo algorithm, we compute the magnetization and susceptibility down to extremely low temperatures while changing the magnitude of both transverse and longitudinal magnetic fields. Several characteristic behaviors are observed, which were not inferred from the previously studied quantum order from disorder at zero temperature, such as a horizontal-type stripe ordering at a substantial longitudinal field and a persistent critical behavior down to low temperature in a weak longitudinal field region.Comment: 6 pages, 5 figures, accepted for publication in J. Phys.: Conf. Se

High-Tc Nodeless s_\pm-wave Superconductivity in (Y,La)FeAsO_{1-y} with Tc=50 K: 75As-NMR Study

We report 75As-NMR study on the Fe-pnictide high-Tc superconductor Y0.95La0.05FeAsO_{1-y} (Y0.95La0.051111) with Tc=50 K that includes no magnetic rare-earth elements. The measurement of the nuclear-spin lattice-relaxation rate 75(1/T1) has revealed that the nodeless bulk superconductivity takes place at Tc=50 K while antiferromagnetic spin fluctuations (AFSFs) develop moderately in the normal state. These features are consistently described by the multiple fully-gapped s_\pm-wave model based on the Fermi-surface (FS) nesting. Incorporating the theory based on band calculations, we propose that the reason that Tc=50 K in Y0.95La0.051111 is larger than Tc=28 K in La1111 is that the FS multiplicity is maximized, and hence the FS nesting condition is better than that in La1111.Comment: 4 pages, 3 figures, accepted for publication in Phys Rev. Let

Drude Weight of the Two-Dimensional Hubbard Model -- Reexamination of Finite-Size Effect in Exact Diagonalization Study --

The Drude weight of the Hubbard model on the two-dimensional square lattice is studied by the exact diagonalizations applied to clusters up to 20 sites. We carefully examine finite-size effects by consideration of the appropriate shapes of clusters and the appropriate boundary condition beyond the imitation of employing only the simple periodic boundary condition. We successfully capture the behavior of the Drude weight that is proportional to the squared hole doping concentration. Our present result gives a consistent understanding of the transition between the Mott insulator and doped metals. We also find, in the frequency dependence of the optical conductivity, that the mid-gap incoherent part emerges more quickly than the coherent part and rather insensitive to the doping concentration in accordance with the scaling of the Drude weight.Comment: 9 pages with 10 figures and 1 table. accepted in J. Phys. Soc. Jp

Competition between unconventional superconductivity and incommensurate antiferromagnetic order in CeRh1-xCoxIn5

Elastic neutron diffraction measurements were performed on the quasi-two dimensional heavy fermion system CeRh1-xCoxIn5, ranging from an incommensurate antiferromagnet for low x to an unconventional superconductor on the Co-rich end of the phase diagram. We found that the superconductivity competes with the incommensurate antiferromagnetic (AFM) order characterized by qI=(1/2, 1/2, delta) with delta=0.298, while it coexists with the commensurate AFM order with qc=(1/2, 1/2, 1/2). This is in sharp contrast to the CeRh1-xIrxIn5 system, where both the commensurate and incommensurate magnetic orders coexist with the superconductivity. These results reveal that particular areas on the Fermi surface nested by qI play an active role in forming the superconducting state in CeCoIn5.Comment: RevTeX4, 4 pages, 4 eps figures; corrected a typo and a referenc

Expression of functional M2 muscarinic acetylcholine receptor in Escherichia coli

The M2 muscarinic acetylcholine receptor mutant (M2 mutant), with a lack of glycosylation sites, a deletion in the central part of the third inner loop, and the addition of a six histidine tag at the C-terminus, was fused to maltose binding protein (MBP) at its N-terminus and expressed in Escherichia coli. The expression level was 0.2 nmol receptor per 100 ml culture, as assessed as [3H]L-quinuclidinyl benzilate ([3H]QNB) binding activity, when the BL 21 strain was cultured at 37 degrees C to a late growth phase and the expression was induced by isopropyl beta-thiogalactoside at 20 degrees C. No [3H]QNB binding activity was detected when it was not fused to MBP or when expression was induced at 37 degrees C instead of 20 degrees C. The MBP-M2 mutant expressed in E. coli showed the same ligand binding activity as the M2 mutant expressed in the Sporodoptera frugiperda (Sf9)/baculovirus system, as assessed as displacement of [(3)H]QNB with carbamylcholine and atropine. The MBP-M2 mutant was solubilized, purified with Co2+-immobilized Chelating Sepharose gel and SP-Sepharose, and then reconstituted into lipid vesicles with G protein Go or Gi1 in the presence or absence of cholesterol. The reconstituted vesicles showed GTP-sensitive high affinity binding for carbamylcholine and carbamylcholine-stimulated [35S]GTP gamma S binding activity in the presence of GDP. The proportion of high affinity sites for carbamylcholine and the extent of carbamylcholine-stimulated [(35)S]GTP gamma S binding were the same as those observed for the M2 mutant expressed in Sf9 cells and were not affected by the presence or absence of cholesterol. These results indicate that the MBP-M2 mutant expressed in E. coli has the same ability to interact with and activate G proteins as the M2 mutant expressed in Sf9, and that cholesterol is not essential for the function of the M2 muscarinic receptor

Magnon softening and damping in the ferromagnetic manganites due to orbital correlations

We present a theory for spin excitations in ferromagnetic metallic manganites and demonstrate that orbital fluctuations have strong effects on the magnon dynamics in the case these compounds are close to a transition to an orbital ordered state. In particular we show that the scattering of the spin excitations by low-lying orbital modes with cubic symmetry causes both the magnon softening and damping observed experimentally.Comment: 2 pages, 2 figures, SCES2003 Roma, to appear in J. Mag. Magn. Ma