NMR evidence of strong-correlated superconductivity in LiFeAs: tuning toward an SDW ordering

In this letter, we reported the results of NMR study on LiFeAs single crystals. We find a strong evidence of the low temperature spin fluctuations; by changing sample preparation conditions, the system can be tuned toward an spin-density-wave (SDW) quantum-critical point. The detection of an interstitial Li(2) ion, possibly locating in the tetrahedral hole, suggests that the off-stoichiometry and/or lattice defect can probably account for the absence of the SDW ordering in LiFeAs. These facts show that LiFeAs is a strongly correlated system and the superconductivity is likely originated from the SDW fluctuations.Comment: 5 pages, s figure

77Se NMR study of pairing symmetry and spin dynamics in KyFe2-xSe2

We present a 77Se NMR study of the newly discovered iron selenide superconductor KyFe2-xSe2, in which Tc = 32 K. Below Tc, the Knight shift 77K drops sharply with temperature, providing strong evidence for singlet pairing. Above Tc, Korringa-type relaxation indicates Fermi-liquid behavior. Our experimental results set strict constraints on the nature of possible theories for the mechanism of high-Tc superconductivity in this iron selenide system.Comment: Chemical composition of crystals determined. Accepted in Physical Review Letter

Atmospheric turbulence and land - atmosphere energy transfer characteristics in the surface layer of the Northern slope of Mt. Qomolangma area : abstract

Based on the turbulent data collected at Quzong site, on the northern slope of Mt. Qomolangma, from April 2005 to March 2006, macro-scale turbulent statistical characteristics and land-atmosphere energy transfer before and after the onset of southwest monsoon were acquired by the eddy correlation method. It was found that Monin-Obukhov similarity theory is applicable for Mt. Qomolangma area. The relationship between normalized wind speed standard deviation and atmospheric stability, variances of normalized temperature and humidity standard deviation with atmospheric stability were simulated in the study. It was also found that energy balance components (net radiation flux, sensible heat flux, latent heat flux and soil heat flux) and surface heating filed had evident diurnal and seasonal changes. Especially under the influence of southwest monsoon, the sensible heat flux and latent heat flux in Quzong area have evident opposite changing trends. The variation characteristics of other surface parameters (surface reflectance and Bowen ratio) is very clear before and after the breakout of southwest monsoon