Effective mass staircase and the Fermi liquid parameters for the fractional quantum Hall composite fermions

Effective mass of the composite fermion in the fractional quantum Hall system, which is of purely interaction originated, is shown, from a numerical study, to exhibit a curious nonmonotonic behavior with a staircase correlated with the number (=2,4,...) of attached flux quanta. This is surprising since the usual composite-fermion picture predicts a smooth behavior. On top of that, significant interactions are shown to exist between composite fermions, where the excitation spectrum is accurately reproduced in terms of Landau's Fermi liquid picture with negative (i.e., Hund's type) orbital and spin exchange interactions.Comment: 4 pages, 3 figures, REVTe

Investigation of the use of microwave image line integrated circuits for use in radiometers and other microwave devices in X-band and above

Program results are described in which the use of a/high permittivity rectangular dielectric image waveguide has been investigated for use in microwave and millimeter wavelength circuits. Launchers from rectangular metal waveguide to image waveguide are described. Theoretical and experimental evaluations of the radiation from curved image waveguides are given. Measurements of attenuation due to conductor and dielectric losses, adhesives, and gaps between the dielectric waveguide and the image plane are included. Various passive components are described and evaluations given. Investigations of various techniques for fabrication of image waveguide circuits using ceramic waveguides are also presented. Program results support the evaluation of the image line approach as an advantageous method for realizing low loss integrated electronic circuits for X-band and above

Static magnetic moments revealed by muon spin relaxation and thermodynamic measurements in quantum spin ice Yb2_2Ti2_2O7_7

We present muon spin relaxation ($\mu$SR) and specific-heat versus temperature $C(T)$ measurements on polycrystalline and single-crystal samples of the pyrochlore magnet Yb$_2$Ti$_2$O$_7$. $C(T)$ exhibits a sharp peak at a $T_\mathrm{C}$ of 0.21 and 0.26~K for the single-crystal and polycrystalline samples respectively. For both samples, the magnetic entropy released between 50~mK and 30~K amounts to $R\ln2$ per Yb. At temperatures below $T_\mathrm{C}$ we observe a steep drop in the asymmetry of the zero-field $\mu$SR time spectra at short time scales, as well as a decoupling of the muon spins from the internal field in longitudinal magnetic fields of $\leq0.25$~T for both the polycrystalline and single-crystal samples. These muon data are indicative of static magnetic moments. Our results are consistent with the onset of long-range magnetic order in both forms of Yb$_2$Ti$_2$O$_7$.Comment: 6 pages, 4 figures, accepted to PR

Spin Chirality Fluctuation and Anomalous Hall Effect in Itinerant Ferromagnets

The anomalous Hall effect due to the spin chirality order and fluctuation is studied theoretically in a Kondo lattice model without the relativistic spin-orbit interaction. Even without the correlations of the localized spins, $\sigma_{xy}$ can emerge depending on the lattice structure and the spin anisotropy. We reveal the condition for this chirality-fluctuation driven mechanism for $\sigma_{xy}$. Our semiquantitative estimates for a pyrochlore oxide Nd$_2$Mo$_2$O$_7$ give a finite \sigma_{xy} \sim 10 \Ohm^{-1} \cm^{-1} together with a high resistivity \rho_{xx} \sim 10^{-4}-10^{-3} \Ohm \cm, in agreement with experiments.Comment: 5 pages, including 4 figure

Mott Transition vs Multicritical Phenomenon of Superconductivity and Antiferromagnetism -- Application to κ\kappa-(BEDT-TTF)2_2X --

Interplay between the Mott transition and the multicritical phenomenon of d-wave superconductivity (SC) and antiferromagnetism (AF) is studied theoretically. We describe the Mott transition, which is analogous to a liquid-gas phase transition, in terms of an Ising-type order parameter $\eta$. We reveal possible mean-field phase diagrams produced by this interplay. Renormalization group analysis up to one-loop order gives flows of coupling constants, which in most cases lead to fluctuation-induced first-order phase transitions even when the SO(5) symmetry exists betwen the SC and AF. Behaviors of various physical quantities around the Mott critical point are predicted. Experiments in $\kappa$-(BEDT-TTF)$_2$X are discussed from this viewpoint.Comment: 4 pages, 9 figures, to appear in J. Phys. Soc. Jp

Two-dimensional charge order in layered 2-1-4 perovskite oxides

Monte Carlo simulations are performed on the three-dimensional (3D) Ising model with the 2-1-4 layered perovskite structure as a minimal model for checkerboard charge ordering phenomena in layered perovskite oxides. Due to the interlayer frustration, only 2D long-range order emerges with a finite correlation length along the c axis. Critical exponents of the transition change continuously as a function of the interlayer coupling constant. The interlayer long-range Coulomb interaction decays exponentially and is negligible even between the second-neighbor layers. Instead, monoclinic distortion of a tetragonal unit cell lifts the macroscopic degeneracy to induce a 3D charge ordering. The dimensionality of the charge order in La$_{0.5}$Sr$_{1.5}$MnO$_4$ is discussed from this viewpoint.Comment: 5 pages including 6 figures, with major changes including discussion on charge ordering phenomena in layered perovskite oxide

Excitation spectrum and effective mass of the even-fraction quantum Hall liquid

To probe the nature of the even-fraction quantum Hall system, we have investigated the low-lying excitation spectrum by means of exact diagonalization for finite systems. We have found (i) a striking one-to-one correspondence (i.e., a shell structure) between the spectrum and those for free (composite) fermions, (ii) a surprisingly straight scaling plot for the excitation energy that gives a zero gap (metal) in the thermodynamic limit, (iii) the effective mass evaluated from the scaling becoming heavier for filling factor = 1/2, 1/4, 1/6, but (iv) some deviations from the single-mode or the Hartree-Fock composite fermion approximation as well.Comment: 4 pages, REVTeX format, 4 eps-figure

Topological nature of polarization and charge pumping in ferroelectrics

Electric polarization or transferred charge due to an adiabatic change of external parameters $\vec{Q}$ is expressed in terms of a vector field defined in the $\vec{Q}$ space. This vector field is characterized by strings, i.e., trajectories of band-crossing points. In particular, the transverse component is given by the Biot-Savart law in a nonlocal way. For a cyclic change of $\vec{Q}$ along a loop C, the linking number between this string and C represents the amount of the pumped charge, which is quantized to be an integer as discussed by Thouless.Comment: 5 pages including 4 figure

Pseudogap Induced Antiferromagnetic Spin Correlation in High-Temperature Superconductors

The pseudogap phenomena observed on cuprate high temperature superconductors are investigated based on the exact diagonalization method on the finite cluster t-J model. The results show the presence of the gap-like behavior in the temperature dependence of various magnetic properties; the NMR relaxation rate, the neutron scattering intensity and the static susceptibility. The calculated spin correlation function indicates that the pseudogap behavior arises associated with the development of the antiferromagnetic spin correlation with decreasing the temperature. The numerical results are presented to clarify the model parameter dependence, that covers the realistic experimental situation. The effect of the next-nearest neighbor hopping $t'$ is also studied.Comment: 7 pages, Revtex, with 10 eps figures, to appear in J. Phys. Soc. Jpn. (Vol. 70, No. 1

Single-crystal growth and magnetic properties of the metallic molybdate pyrochlore Sm2Mo2O7

We have successfully grown cm3-size single crystals of the metallic-ferromagnet Sm2Mo2O7 by the floating-zone method using an infrared-red image furnace. The growth difficulties and the remedies found using a 2-mirror image furnace are discussed. Magnetization studies along the three crystalline axes of the compound are presented and discussed based on our recent proposal of an ordered spin-ice ground state for this compoun