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The single electron tunneling spectroscopy on superconductor Na$_{x}$CoO$_2$$cdot$ yH$_2$O and its starting compound Na$_{x}$CoO$_2$ has been studied with point-contact method. The spectra of Na$_{x}$CoO$_2$ have two types of distinct shapes at different random locations, this is attributed to the non-uniformly distributed sodium escaped from the inner part of the sample. While all the measured spectra of the superconducting samples Na$_{x}$CoO$_2$$cdot$ yH$_2$O have a good spatial reproducibility, and show a remarkable zero bias conductance depression appearing below an onset temperature which associates very well with the resistance upturn at around 45 K. The latter behavior resembles in some way the pseudogap feature in high-T$_c$ cuprate uperconductors.
We report on first investigation of the lattice dynamics in the novel superconducting material Na$_{0.35}$CoO$_2$$cdot$1.3H$_2$O and the non-hydrated parent compound Na$_{0.7}$CoO$_2$ by inelastic x-ray scattering. The measured phonon dispersion alon
A weak magnetic order was found in a non-superconducting bilayered-hydrate Na$_{x}$CoO$_{2}cdot y$H$_{2}$O sample by a Co Nuclear Quadrupole Resonance (NQR) measurement. The nuclear spin-lattice relaxation rate divided by temperature $1/T_1T$ shows a
It has often been suggested that correlation effects suppress the small e_g Fermi surface pockets of NaxCoO_2 that are predicted by LDA, but absent in ARPES measurements. It appears that within the dynamical mean field theory (DMFT) the ARPES can be
We report inelastic x-ray scattering measurements of the in-plane polarized transverse acoustic phonon mode propagating along $qparallel$[100] in various hole-doped compounds belonging to the 122 family of iron-based superconductors. The slope of the
We have studied the superconducting phase diagram of NaHspace as a function of electronic doping, characterizing our samples both in terms of Na content $x$ and the Co valence state. Our findings are consistent with a recent report that intercalation