Universal Finite-Size Scaling Function of the Ferromagnetic Heisenberg Chain in a Magnetic Field,

The finite-size scaling function of the magnetization of the ferromagnetic Heisenberg chain is argued to be universal with respect to the magnitude of the spin. The finite-size scaling function is given explicitly by an analytical calculation in the classical limit $S=\infty.$ The universality is checked for $S=1/2$ and $1$ by means of numerical calculations. Critical exponents are obtained as well. It is concluded that this universal scaling function originates in the universal behavior of the correlation function.Comment: 14 pages (revtex 2.0) + 8 PS figures upon request

59Co Nuclear Quadrupole Resonance Studies of Superconducting and Non-superconducting Bilayer Water Intercalated Sodium Cobalt Oxides NaxCoO2.yH2O

We report 59Co nuclear quadrupole resonance (NQR) studies of bilayer water intercalated sodium cobalt oxides NaxCoO2.yH2O (BLH) with the superconducting transition temperatures, 2 K < T_c <= 4.6 K, as well as a magnetic BLH sample without superconductivity. We obtained a magnetic phase diagram of T_c and the magnetic ordering temperature T_M against the peak frequency nu_3 59Co NQR transition I_z = +- 5/2 +-7/2 and found a dome shape superconducting phase. The 59Co NQR spectrum of the non-superconducting BLH shows a broadening below T_M without the critical divergence of 1/T_1 and 1/T_2, suggesting an unconventional magnetic ordering. The degree of the enhancement of 1/T_1T at low temperatures increases with the increase of nu_3 though the optimal nu_3~12.30 MHz. In the NaxCoO2.yH2O system, the optimal-T_c superconductivity emerges close to the magnetic instability. T_c is suppressed near the phase boundary at nu_3~12.50 MHz, which is not a conventional magnetic quantum critical point.Comment: 4 pages, 5 figure

59Co-NMR Knight Shift of Superconducting Three-Layer NaxCoO2.yH2O

The superconducting state of NaxCoO2.yH2O with three CoO2 layers in a unit cell has been studied by 59Co-NMR. The Knight shift measured for a peak of the NMR spectra corresponding to the external magnetic field H along one of the principal directions within the CoO2 plane, exhibits a rapid decrease with decreasing temperature T below the superconducting transition temperature Tc, indicating that the spin susceptibility is suppressed in the superconducting phase, at least, for this field direction. Because differences of the superconducting properties are rather small between this three-layer NaxCoO2.yH2O and previously reported NaxCoO2.yH2O with two CoO2 layers within a unit cell, the present result of the Knight shift studies indicates that the Cooper pairs of the former system are in the singlet state as in the latter, for which the spin susceptibility is suppressed for both directions of H parallel and perpendicular to the CoO2 plane.Comment: 5 page

Delta-like and gtl2 are reciprocally expressed, differentially methylated linked imprinted genes on mouse chromosome 12

AbstractThe distal portion of mouse chromosome 12 is imprinted. To date, however, Gtl2 is the only imprinted gene identified on chromosome 12. Gtl2 encodes multiple alternatively spliced transcripts with no apparent open reading frame. Using conceptuses with maternal or paternal uniparental disomy for chromosome 12 (UPD12), we found that Gtl2 is expressed from the maternal allele and methylated at the 5′ end of the silent paternal allele. A reciprocally imprinted gene, Delta-like (Dlk), with homology to genes involved in the Notch signalling pathway was identified 80kb upstream of Gtl2. Dlk was expressed exclusively from the paternal allele in both the embryo and placenta, but the CpG-island promoter of Dlk was completely unmethylated on both parental alleles. Rather, a paternally methylated region was identified in the last exon of the active Dlk allele. The proximity, reciprocal imprinting and methylation in this domain are reminiscent of the co-ordinately regulated Igf2–H19 imprinted domain on mouse chromosome 7. Like H19 and Igf2, Gtl2 and Dlk were found to be co-expressed in the same tissues throughout development, though not after birth. These results have implications for the regulation, function and evolution of imprinted domains

Time-Dependent Density-Functional Theory for the Stopping Power of an Interacting Electron Gas for Slow Ions

Based on the time-dependent density-functional theory, we have derived a rigorous formula for the stopping power of an {\it interacting} electron gas for ions in the limit of low projectile velocities. If dynamical correlation between electrons is not taken into account, this formula recovers the corresponding stopping power of {\it noninteracting} electrons in an effective Kohn-Sham potential. The correlation effect, specifically the excitonic one in electron-hole pair excitations, however, is found to considerably enhance the stopping power for intermediately charged ions, bringing our theory into good agreement with experiment.Comment: 4 pages, 1 figure, Accepted to Phys. Rev. B (Rapid Communication

Weak Magnetic Order in the Bilayered-hydrate Nax_{x}CoO2⋅y_{2}\cdot yH2_{2}O Structure Probed by Co Nuclear Quadrupole Resonance - Proposed Phase Diagram in Superconducting Nax_xCoO2⋅_{2} \cdot yyH2_2O

A weak magnetic order was found in a non-superconducting bilayered-hydrate Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O sample by a Co Nuclear Quadrupole Resonance (NQR) measurement. The nuclear spin-lattice relaxation rate divided by temperature $1/T_1T$ shows a prominent peak at 5.5 K, below which a Co-NQR peak splits due to an internal field at the Co site. From analyses of the Co NQR spectrum at 1.5 K, the internal field is evaluated to be $\sim$ 300 Oe and is in the $ab$-plane. The magnitude of the internal field suggests that the ordered moment is as small as $\sim 0.015$ $\mu_B$ using the hyperfine coupling constant reported previously. It is shown that the NQR frequency $\nu_Q$ correlates with magnetic fluctuations from measurements of NQR spectra and $1/T_1T$ in various samples. The higher-$\nu_Q$ sample has the stronger magnetic fluctuations. A possible phase diagram in Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O is depicted using $T_c$ and $\nu_Q$, in which the crystal distortion along the c-axis of the tilted CoO$_2$ octahedron is considered to be a physical parameter. Superconductivity with the highest $T_c$ is seemingly observed in the vicinity of the magnetic phase, suggesting strongly that the magnetic fluctuations play an important role for the occurrence of the superconductivity.Comment: 5 pages, 6 figures, submitted to J. Phys. Soc. Jp

Non-universal transmission phase behaviour of a large quantum dot

The electron wave function experiences a phase modification at coherent transmission through a quantum dot. This transmission phase undergoes a characteristic shift of $\pi$ when scanning through a Coulomb-blockade resonance. Between successive resonances either a transmission phase lapse of $\pi$ or a phase plateau is theoretically expected to occur depending on the parity of the corresponding quantum dot states. Despite considerable experimental effort, this transmission phase behaviour has remained elusive for a large quantum dot. Here we report on transmission phase measurements across such a large quantum dot hosting hundreds of electrons. Using an original electron two-path interferometer to scan the transmission phase along fourteen successive resonances, we observe both phase lapses and plateaus. Additionally, we demonstrate that quantum dot deformation alters the sequence of transmission phase lapses and plateaus via parity modifications of the involved quantum dot states. Our findings set a milestone towards a comprehensive understanding of the transmission phase of quantum dots.Comment: Main paper: 18 pages, 5 figures, Supplementary materials: 8 pages, 4 figure

Novel phase diagram of superconductor NaxCoO2-yH2O in a 75 % relative humidity

We succeeded in synthesizing the powder samples of bilayer-hydrate sodium cobalt oxide superconductors NaxCoO2-yH2O with Tc = 0 ~ 4.6 K by systematically changing the keeping duration in a 75 % relative humidity atmosphere after intercalation of water molecules. From the magnetic measurements, we found that the one-day duration sample does not show any superconductivity down to 1.8 K, and that the samples kept for 2 ~ 7 days show superconductivity, in which Tc increases up to 4.6 K with increasing the duration. Tc and the superconducting volume fraction are almost invariant between 7 days and 1month duration. The 59Co NQR spectra indicate a systematic change in the local charge distribution on the CoO2 plane with change in duration.Comment: 4 pages, 5 figures, submitted to Journal of the Physical Society of Japa

Possible Pairing Symmetry of Superconductor Na_xCoO_2yH_2O

To discuss a possibility that the superconductivities in Na_xCoO_2yH_2O are induced by the electron correlation, we investigate the possible pairing symmetry based on the single-band Hubbard model whose dispersion of the bare energy band is obtained by using FLAPW-LDA band structure calculation of Na_xCoO_2yH_2O. The superconducting transition temperature is estimated by solving the Eliashberg equation. In this equation, both normal and anomalous self-energies are calculated up to the third-order terms with respect to the Coulomb repulsion. In the case of spin-singlet pairing, the candidate of pairing symmetry (the maximum eigen value \lambda_max^SS of Eliashberg's equation) belongs to d-wave(E_2 representation of D_6 group). In the case of spin-triplet pairing, the candidate of pairing symmetry (the maximum eigen value \lambda_max^ST of Eliashberg's equation) belongs to f_{y(y^{2}-3x^{2})}-wave (B_1 representation of D_6 group). It is found that \lambda_max^SS\simeq\lambda_max^ST and the transition temperatures of unconventional pairing state are estimated to be low compared with observed temperature within our simple model.Comment: 10 pages, 5 figure