Sliding Density-Wave in Sr_{14}Cu_{24}O_{41} Ladder Compounds

We used transport and Raman scattering measurements to identify the insulating state of self-doped spin 1/2 two-leg ladders of Sr_{14}Cu_{24}O_{41} as a weakly pinned, sliding density wave with non-linear conductivity and a giant dielectric response that persists to remarkably high temperatures

Stoner gap in the superconducting ferromagnet UGe2

We report the temperature ($T$) dependence of ferromagnetic Bragg peak intensities and dc magnetization of the superconducting ferromagnet UGe2 under pressure ($P$). We have found that the low-$T$ behavior of the uniform magnetization can be explained by a conventional Stoner model. A functional analysis of the data produces the following results: The ferromagnetic state below a critical pressure can be understood as the perfectly polarized state, in which heavy quasiparticles occupy only majority spin bands. A Stoner gap $\Delta(P)$ decreases monotonically with increasing pressure and increases linearly with magnetic field. We show that the present analysis based on the Stoner model is justified by a consistency check, i.e., comparison of density of states at the Fermi energy deduced from the analysis with observed electronic specific heat coeffieients. We also argue the influence of the ferromagnetism on the superconductivity.Comment: 5 pages, 4 figures. to be published in Phys. Rev.

Manifestation of spin-charge separation in the dynamic dielectric response of one--dimensional Sr2CuO3

We have determined the dynamical dielectric response of a one-dimensional, correlated insulator by carrying out electron energy-loss spectroscopy on Sr2CuO3 single crystals. The observed momentum and energy dependence of the low-energy features, which correspond to collective transitions across the gap, are well described by an extended one-band Hubbard model with moderate nearest neighbor Coulomb interaction strength. An exciton-like peak appears with increasing momentum transfer. These observations provide experimental evidence for spin-charge separation in the relevant excitations of this compound, as theoretically expected for the one-dimensional Hubbard model.Comment: RevTex, 4 pages+2 figures, to appear in PRL (July 13

Electrical Resistivity and Thermal Expansion Measurements of URu2Si2 under Pressure

We carried out simultaneous measurements of electrical resistivity and thermal expansion of the heavy-fermion compound URu2Si2 under pressure using a single crystal. We observed a phase transition anomaly between hidden (HO) and antiferromagnetic (AFM) ordered states at TM in the temperature dependence of both measurements. For the electrical resistivity, the anomaly at TM was very small compared with the distinct hump anomaly at the phase transition temperature T0 between the paramagnetic state (PM) and HO, and exhibited only a slight increase and decrease for the I // a-axis and c-axis, respectively. We estimated each excitation gap of HO, Delta_HO, and AFM, Delta_AFM, from the temperature dependence of electrical resistivity; Delta_HO and Delta_AFM have different pressure dependences from each other. On the other hand, the temperature dependence of thermal expansion exhibited a small anomaly at T0 and a large anomaly at TM. The pressure dependence of the phase boundaries of T0 and TM indicates that there is no critical end point and the two phase boundaries meet at the critical point.Comment: 4 pages, 4 figure

Volcanic synchronization of Dome Fuji and Dome C Antarctic deep ice cores over the past 216 kyr

Abstract. Two deep ice cores, Dome Fuji (DF) and EPICA Dome C (EDC), drilled at remote dome summits in Antarctica, were synchronized to better understand their chronology. A total of 1401 volcanic tie points were identified covering the past 216 kyr. DFO2006, the chronology for the DF core characterized by strong constraining by the O2/N2 age markers, was compared with AICC2012, the chronology for 5 cores including the EDC core, and characterized by glaciological approaches combining ice flow modelling with various age markers. The age gaps between the two chronologies are within 2 kyr, except at Marine Isotope Stage (MIS) 5. DFO2006 gives ages older than AICC2012, with peak values of the gap of 4.5 and 3.1 kyr at MIS 5d and MIS 5b, respectively. Accordingly, ratios of duration DFO2006/AICC2012 are 85% at a period from the late stage of MIS 6 to MIS 5d and 114% at a period from MIS 5d to 5b. We then compared the DFO2006 with another chronology of the DF core, DFGT2006, characterized by glaciological approaches with weaker constraining by age markers. Features of the DFO2006/DFGT2006 age gaps are very similar to those of the DFO2006/AICC2012 age gaps. This fact lead us to hypothesize that a cause of the systematic DFO2006/AICC2012 age gaps at MIS 5 are associated with differences in the dating approaches. Besides, ages of speleothem records from China agreed well with DFO2006 at MIS 5c and 5d but not at MIS 5b. Thus, we hypothesize at least at MIS 5c and 5d, major sources of the gaps are systematic errors in surface mass balance estimation in the glaciological approach. Compatibility of the age markers should be carefully assessed in future. This work is a contribution to the European Project for Ice Coring in Antarctica (EPICA), a joint European Science Foundation/European Commission scientific program, funded by the European Union and by national contributions from Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Sweden, Switzerland and the United Kingdom. This study was supported in part by a Grant-in-Aid for Scientific Research (A) (20241007) from the Japan Society for the Promotion of Science (JSPS).This is the final version of the article. It first appeared from Copernicus Publications via http://dx.doi.org/10.5194/cpd-11-407-201

Ultrafast optical nonlinearity in quasi-one-dimensional Mott-insulator Sr2CuO3{\rm Sr_2CuO_3}

We report strong instantaneous photoinduced absorption (PA) in the quasi-one-dimensional Mott insulator ${\rm Sr_2CuO_3}$ in the IR spectral region. The observed PA is to an even-parity two-photon state that occurs immediately above the absorption edge. Theoretical calculations based on a two-band extended Hubbard model explains the experimental features and indicates that the strong two-photon absorption is due to a very large dipole-coupling between nearly degenerate one- and two-photon states. Room temperature picosecond recovery of the optical transparency suggests the strong potential of ${\rm Sr_2CuO_3}$ for all-optical switching.Comment: 10 pages, 4 figure