Enhancing the Superconducting Transition Temperature due to Strong-Coupling Effect under Antiferromagnetic Spin Fluctuations in CeRh1-xIrxIn5 : 115In-NQR Study

We report on systematic evolutions of antiferromagnetic (AFM) spin fluctuations and unconventional superconductivity (SC) in heavy-fermion (HF) compounds CeRh$_{1-x}$Ir$_{x}$In$_5$ via $^{115}$In nuclear-quadrupole-resonance (NQR) experiment. The measurements of nuclear spin-lattice relaxation rate $1/T_1$ have revealed the marked development of AFM spin fluctuations as a consequence of approaching an AFM ordered state with increasing Rh content. Concomitantly the superconducting transition temperature $T_{\rm c}$ and the energy gap $\Delta_0$ increase drastically from $T_{\rm c} = 0.4$ K and $2\Delta_0/k_{\rm B}T_{\rm c} = 5$ in CeIrIn$_5$ up to $T_{\rm c} = 1.2$ K and $2\Delta_0/k_{\rm B}T_{\rm c} = 8.3$ in CeRh$_{0.3}$Ir$_{0.7}$In$_5$, respectively. The present work suggests that the AFM spin fluctuations in close proximity to the AFM quantum critical point are indeed responsible for the onset of strong-coupling unconventional SC with the line node in the gap function in HF compounds.Comment: 4pages,5figures,to appear in Phys. Rev. Let

Planar CuO_2 hole density estimation in multilayered high-T_c cuprates

We report that planar CuO_2 hole densities in high-T_c cuprates are consistently determined by the Cu-NMR Knight shift. In single- and bi-layered cuprates, it is demonstrated that the spin part of the Knight shift K_s(300 K) at room temperature monotonically increases with the hole density $p$ from underdoped to overdoped regions, suggesting that the relationship of K_s(300 K) vs. p is a reliable measure to determine p. The validity of this K_s(300 K)-p relationship is confirmed by the investigation of the p-dependencies of hyperfine magnetic fields and of spin susceptibility for single- and bi-layered cuprates with tetragonal symmetry. Moreover, the analyses are compared with the NMR data on three-layered Ba_2Ca_2Cu_3O_6(F,O)_2, HgBa_2Ca_2Cu_3O_{8+delta}, and five-layered HgBa_2Ca_4Cu_5O_{12+delta}, which suggests the general applicability of the K_s(300 K)-p relationship to multilayered compounds with more than three CuO_2 planes. We remark that the measurement of K_s(300 K) enables us to separately estimate p for each CuO_2 plane in multilayered compounds, where doped hole carriers are inequivalent between outer CuO_2 planes and inner CuO_2 planes.Comment: 7 pages, 5 figures, 2 Tables, to be published in Physical Review

Novel Superconducting Phases in Copper Oxides and Iron-oxypnictides: NMR Studies

We reexamine the novel phase diagrams of antiferromagnetism (AFM) and high-Tc$superconductivity (HTSC) for a disorder-free CuO$_2$plane based on an evaluation of local hole density ($p$) by site-selective Cu-NMR studies on multilayered copper oxides. Multilayered systems provide us with the opportunity to research the characteristics of the disorder-free CuO$_2$plane. The site-selective NMR is the best and the only tool used to extract layer-dependent characteristics. Consequently, we have concluded that the uniform mixing of AFM and SC is a general property inherent to a single CuO$_2$plane in an underdoped regime of HTSC. The$T$=0 phase diagram of AFM constructed here is in quantitative agreement with the theories in a strong correlation regime which is unchanged even with mobile holes. This {\it Mott physics} plays a vital role for mediating the Cooper pairs to make$T_c$of HTSC very high. By contrast, we address from extensive NMR studies on electron-doped iron-oxypnictides La1111 compounds that the increase in$T_c$is not due to the development of AFM spin fluctuations, but because the structural parameters, such as the bond angle$\alpha$of the FeAs$_4$tetrahedron and the a-axis length, approach each optimum value. Based on these results, we propose that a stronger correlation in HTSC than in FeAs-based superconductors may make$T_c$ higher significantly.Comment: 5 pages, 4 figures, accepted for publication in J.Phys.Chem.Solids (2010

Evolutional Science and Engineering of Correlated Electron Matter

New types of superconducting and magnetic phenomena emerge in correlated electron matters. Strong electron-correlation effect gives rich phenomena and functions in condensed matters, being key-concept for heavy-electron materials, itinerant electron magnets, high-transition-temperature cupper-oxide superconductors, novel transition- metal oxides, and organic conductors, magnets and superconductors.We begin with a perspective view on these materials. An overview on experimental techniques, that are powerful tools for investigating these phenomena, are given, focusing on Nuclear Magnetic Resonance (NMR) and Neutron Scattering (NS) experiments. On the basis of microscopic information obtained by these techniques, we address intriguing properties in correlated electron matters and their physical backgrounds. The important functions and central physics of superconductivity are reviewed on conventional materials so as to be able to capture its basic concept. Strongly correlated superconductivity is also remarked for understanding of a new concept for superconductivity mediated by magnetic interactions. Potential application of correlated electron matters to technology is presented focusing on "Spintronics" or "Strongly Correlated Electronics."大阪大学OpenCourseWare:大学院講義 (留学生向け特別プログラムから

Numerical Evaluation of the Impact of Urbanization on Summertime Precipitation in Osaka, Japan

This study utilized the Weather Research and Forecasting (WRF) model version 3.5.1 to evaluate the impact of urbanization on summertime precipitation in Osaka, Japan. The evaluation was conducted by comparing the WRF simulations with the present land use and no-urban land use (replacing “Urban” with “Paddy”) for August from 2006 to 2010. The urbanization increased mean air temperature by 2.1°C in urban areas because of increased sensible heat flux and decreased mean humidity by 0.8 g kg−1 because of decreased latent heat flux. In addition, the urbanization increased duration of the southwesterly sea breeze. The urbanization increased precipitation in urban areas and decreased in the surrounding areas. The mean precipitation in urban areas was increased by 20 mm month−1 (27% of the total amount without the synoptic-scale precipitation). The precipitation increase was generally due to the enhancement of the formation and development of convective clouds by the increase in sensible heat flux during afternoon and evening time periods. The urbanization in Osaka changes spatial and temporal distribution patterns of precipitation and evaporation, and consequently it substantially affects the water cycle in and around the urban areas of Osaka