Analysis of the spectral function of Nd1.85Ce0.15CuO4, obtained by angle resolved photoemission spectroscopy

Samples of Nd(2-x)Ce(x)CuO(4), an electron-doped high temperature superconducting cuprate (HTSC), near optimal doping at x = 0.155 were measured via angle resolved photoemission (ARPES). We report a renormalization feature in the self energy ("kink") in the band dispersion at 50 - 60 meV present in nodal and antinodal cuts across the Fermi surface. Specifically, while the kink had previously only been seen in the antinodal region, it is now observed also in the nodal region, reminiscent of what has been observed in hole-doped cuprates.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

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

第6回極域科学シンポジウム[OM] 極域気水圏11月16日（月）　国立極地研究所１階交流アトリウ

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

Examining the Connections within the Startup Ecosystem: A Case Study of St. Louis

This paper documents the resurgence of entrepreneurial activity in St. Louis by reporting on the collaboration and local learning within the startup community. This activity is happening both between entrepreneurs and between organizations that provide support, such as mentoring and funding, to entrepreneurs. As these connections deepen, the strength of the entrepreneurial ecosystem grows. Another finding from the research is that activity-based events, where entrepreneurs have the chance to use and practice the skills needed to grow their businesses, are most useful. St. Louis provides a multitude of these activities, such as Startup Weekend, 1 Million Cups, Code Until Dawn, StartLouis, and GlobalHack. Some of these are St. Louis specific, but others have nationwide or global operations, providing important implications for other cities

Microwave and millimeter wave spectroscopy in the slightly hole-doped ladders of Sr14_{14}Cu24_{24}O41_{41}

We have measured the temperature- and frequency dependence of the microwave and millimeter wave conductivity $\sigma_1(T,\omega)$ along both the ladder (c-axis) and the leg (a-axis) directions in Sr$_{14}$Cu$_{24}$O$_{41}$. Below a temperature $T^*$($\sim$170 K), we observed a stronger frequency dependence in $\sigma_1^c(T,\omega)$ than that in $\sigma_1^a(T,\omega)$, forming a small resonance peak developed between 30 GHz and 100 GHz. We also observed nonlinear dc conduction along the c-axis at rather low electric fields below $T^*$. These results suggest some collective excitation contributes to the c-axis charge dynamics of the slightly hole-doped ladders of Sr$_{14}$Cu$_{24}$O$_{41}$ below $T^*$.Comment: 7 pages, 4 figure, to be published in Europhysics Letter

Possible manifestation of spin fluctuations in the temperature behavior of resistivity in Sm_{1.85}Ce_{0.15}CuO_4 thin films

A pronounced step-like (kink) behavior in the temperature dependence of resistivity $\rho (T)$ is observed in the optimally-doped $Sm_{1.85}Ce_{0.15}CuO_4$ thin films around $T_{sf}=87K$ and attributed to manifestation of strong spin fluctuations induced by $Sm^{3+}$ moments with the energy $\hbar \omega_{sf}=k_BT_{sf}\simeq 7meV$. In addition to fluctuation induced contribution $\rho_{sf}(T)$ due to thermal broadening effects (of the width $\omega_{sf}$), the experimental data are found to be well fitted accounting for residual (zero-temperature) $\rho_{res}$, electron-phonon $\rho _{e-ph}(T)=AT$ and electron-electron $\rho_{e-e}(T)=BT^2$ contributions. The best fits produced $\omega_p=2.1meV$, $\tau_0^{-1}=9.5\times 10^{-14}s^{-1}$, $\lambda =1.2$, and $E_F=0.2eV$ for estimates of the plasmon frequency, the impurity scattering rate, electron-phonon coupling constant, and the Fermi energy, respectively.Comment: 6 pages (REVTEX4), 2 EPS figures; accepted for publication in JETP Letter

Superconductivity of the Sr2Ca12Cu24O41Sr_2 Ca_{12} Cu_{24} O_{41} spin ladder system: Are the superconducting pairing and the spin-gap formation of the same origin?

Pressure-induced superconductivity in a spin-ladder cuprate Sr$_2$Ca$_{12}$Cu$_{24}$O$_{41}$ has not been studied on a microscopic level so far although the superconductivity was already discovered in 1996. We have improved high-pressure technique with using a large high-quality crystal, and succeeded in studying the superconductivity using $^{63}$Cu nuclear magnetic resonance (NMR). We found that anomalous metallic state reflecting the spin-ladder structure is realized and the superconductivity possesses a s-wavelike character in the meaning that a finite gap exists in the quasi-particle excitation: At pressure of 3.5GPa we observed two excitation modes in the normal state from the relaxation rate $T_1^{-1}$. One gives rise to an activation-type component in $T_1^{-1}$, and the other $T$-linear component linking directly with the superconductivity. This gapless mode likely arises from free motion of holon-spinon bound states appearing by hole doping, and the pairing of them likely causes the superconductivity.Comment: to be published in Phys. Rev. Let