Emergent Phases of Nodeless and Nodal Superconductivity Separated by Antiferromagnetic Order in Iron-based Superconductor (Ca4Al2O6)Fe2(As1-xPx)2: 75As- and 31P-NMR Studies

We report $^{31}$P- and $^{75}$As-NMR studies on (Ca$_4$Al$_2$O$_{6}$)Fe$_2$(As$_{1-x}$P$_x$)$_2$ with an isovalent substitution of P for As. We present the novel evolution of emergent phases that the nodeless superconductivity (SC) in 0$\le x \le$0.4 and the nodal one around $x$=1 are intimately separated by the onset of a commensurate stripe-type antiferromagnetic (AFM) order in 0.5$\le x \le$ 0.95, as an isovalent substitution of P for As decreases a pnictogen height $h_{Pn}$ measured from the Fe plane. It is demonstrated that the AFM order takes place under a condition of 1.32\AA$\le h_{Pn} \le$1.42\AA, which is also the case for other Fe-pnictides with the Fe$^{2+}$ state in (Fe$Pn$)$^{-}$ layers. This novel phase evolution with the variation in $h_{Pn}$ points to the importance of electron correlation for the emergence of SC as well as AFM order.Comment: 5pages, 4figures; accepted for publication as a Rapid Communication in Phys. Rev.

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

Assessment of first derivative of doppler blood flow velocity in vascular aging

The aim of this study is to determine the first derivative of blood flow velocity (FDBFV) in common carotid artery (CCA) in order to evaluate cardiovascular functions. The extracted derivative of the velocity is suggested the acceleration waves which able to provide an aging index (AGI) in the cardiovascular system. In the study, acceleration wave derived from FDBFV consist of a, b, c, d, e and f waves which represent the initial positive, early negative, re-increasing, late re-decreasing, diastolic positive waves and diastolic negative waves, respectively. The FDBFV waveforms of 227 healthy volunteers are statistically analyzed in the study. Pearson’s correlation analysis is used to determine the relationship between all variables and factors on the selected hemodynamic data. In the study, there are significant difference (r=0.727, p<0.001) of AGI in FDBFV. We found that f wave in FDBFV waveform shows strong correlation (p< 0.001) to blood pressure. In conclusion, the potential of FDBFV in CCA is an effective method to evaluate the vascular aging

Antiferromagnetic Spin Fluctuations and Unconventional Nodeless Superconductivity in an Iron-based New Superconductor (Ca_4Al_2O_{6-y})(Fe_2As_2):75As-NQR Study

We report 75As-nuclear quadrupole resonance (NQR) studies on (Ca_4Al_2O_{6-y})(Fe_2As_2) with Tc=27K, which unravel unique normal-state properties and point to unconventional nodeless superconductivity (SC). Measurement of nuclear-spin-relaxation rate 1/T_1 has revealed a significant development of two dimensional (2D) antiferromagnetic (AFM) spin fluctuations down to Tc, in association with the fact that FeAs layers with the smallest As-Fe-As bond angle are well separated by thick perovskite-type blocking layer. Below Tc, the temperature dependence of 1/T_1 without any trace of the coherence peak is well accounted for by an s(+-)-wave multiple gaps model. From the fact that Tc=27K in this compound is comparable to Tc=28K in the optimally-doped LaFeAsO_{1-y} in which AFM spin fluctuations are not dominant, we remark that AFM spin fluctuations are not a unique factor for enhancing Tc among existing Fe-based superconductors, but a condition for optimizing SC should be addressed from the lattice structure point of view.Comment: 4pages, 4figures, accepted for publication in Phys. Rev. Let

On-line learning of non-monotonic rules by simple perceptron

We study the generalization ability of a simple perceptron which learns unlearnable rules. The rules are presented by a teacher perceptron with a non-monotonic transfer function. The student is trained in the on-line mode. The asymptotic behaviour of the generalization error is estimated under various conditions. Several learning strategies are proposed and improved to obtain the theoretical lower bound of the generalization error.Comment: LaTeX 20 pages using IOP LaTeX preprint style file, 14 figure

On-Line AdaTron Learning of Unlearnable Rules

We study the on-line AdaTron learning of linearly non-separable rules by a simple perceptron. Training examples are provided by a perceptron with a non-monotonic transfer function which reduces to the usual monotonic relation in a certain limit. We find that, although the on-line AdaTron learning is a powerful algorithm for the learnable rule, it does not give the best possible generalization error for unlearnable problems. Optimization of the learning rate is shown to greatly improve the performance of the AdaTron algorithm, leading to the best possible generalization error for a wide range of the parameter which controls the shape of the transfer function.)Comment: RevTeX 17 pages, 8 figures, to appear in Phys.Rev.

Unconventional multiband superconductivity with nodes in single-crystalline SrFe2(As_0.65P_0.35)2 as seen via 31P-NMR and specific heat

We report 31P-NMR and specific heat measurements on an iron (Fe)-based superconductor SrFe2(As0.65P0.35)2 with Tc=26 K, which have revealed the development of antiferromagnetic correlations in the normal state and the unconventional superconductivity(SC) with nodal gap dominated by the gapless low-lying quasiparticle excitations. The results are consistently argued with an unconventional multiband SC state with the gap-size ratio of different bands being significantly large; the large full gaps in s\pm-wave state keep Tc high, whereas a small gap with a nodal-structure causes gapless feature under magnetic field. The present results will develop an insight into the strong material dependence of SC-gap structure in Fe-based superconductors.Comment: 6 pages, 5 figures, 1 tabl

Globally optimal on-line learning rules for multi-layer neural networks

We present a method for determining the globally optimal on-line learning rule for a soft committee machine under a statistical mechanics framework. This rule maximizes the total reduction in generalization error over the whole learning process. A simple example demonstrates that the locally optimal rule, which maximizes the rate of decrease in generalization error, may perform poorly in comparison

Antiferromagnetic Order and Superconductivity in Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 with Electron Doping: 75As-NMR Study

We report an 75As-NMR study on iron (Fe)-based superconductors with thick perovskitetype blocking layers Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 with x=0 and 0.2. We have found that antiferromagnetic (AFM) order takes place when x=0, and superconductivity (SC) emerges below Tc=36 K when x=0.2. These results reveal that the Fe-pnictides with thick perovskitetype blocks also undergo an evolution from the AFM order to the SC by doping electron carriers into FeAs planes through the chemical substitution of Ti+4 ions for Mg+2 ions, analogous to the F-substitution in LaFeAsO compound. The reason why the Tc=36 K when x=0.2 being higher than the optimally electron-doped LaFeAsO with Tc=27 K relates to the fact that the local tetrahedron structure of FeAs4 is optimized for the onset of SC.Comment: 4 pages, 3 figures, 1 tabl

75As NQR/NMR Studies on Oxygen-deficient Iron-based Oxypnictide Superconductors LaFeAsO_{1-y} (y=0,0.25,0.4) and NdFeAsO_{0.6}

We report 75As-NQR/NMR studies on the oxygen-deficient iron(Fe)-based oxypnictide superconductors LaFeAsO_{0.6} (T_c=28 K) along with the results on LaFeAsO, LaFeAsO_{0.75}(T_c=20 K) and NdFeAsO_{0.6}(T_c=53 K). Nuclear spin-lattice relaxation rate 1/T_1 of 75As NQR at zero field on LaFeAsO_{0.6} has revealed a T^3 dependence below T_c upon cooling without the coherence peak just below T_c, evidencing the unconventional superconducting state with the line-node gap. We have found an intimate relationship between the nuclear quadrupole frequencyof 75As and T_c for four samples used in this study. It implies microscopically that the local configuration of Fe and As atoms is significantly related to the T_c of the Fe-oxypnictide superconductors, namely, the T_c can be enhanced up to 50 K when the local configuration of Fe and As atoms is optimal, in which the band structure may be also optimized through the variation of hybridization between As 4p orbitals and Fe 3d orbitals.Comment: 4 pages, 5 figures, Accepted for publication in J. Phys. Soc. Jpn., vol.77, No.