NMR evidence for Mott-Hubbard localization in (NH3)K3C60

13C, 1H, and 39K-NMR measurements of (NH3)K3C60 unambiguously demonstrated that its magnetic properties are described as a S=1/2 localized spin system over the entire temperature range (300 K–4.2 K). A possible antiferromagnetic structure that appeared below 45 K is compatible with the orientational order of K-NH3 pairs on the octahedral (O) site. The present NMR study strongly suggests that the Mott-Hubbard localization occurs due to the removal of the C60 t1u-orbital degeneracy

Evidence for quasi-two-dimensional superconductivity in electron-doped Li0.48(THF)yHfNCl

Dc-magnetization and NMR measurements were carried out on a layered superconductor Li0.48(THF)yHfNCl having Tc∼26 K. For the magnetic field applied perpendicular to the basal plane (ab plane) above 10 kOe, we found a pronounced broadening of the superconducting transition in temperature dependence of magnetization and the substantial diamagnetic signals were observed as high as 2Tc, indicating the existence of superconducting fluctuations. Analysis based on the anisotropic Ginzburg-Landau model reveals that the present system is a highly anisotropic superconductor. 7Li-NMR signals were observed around zero Knight shift, indicating that the local Fermi-level density of states, N(EF), at Li site is practically nothing and the superconductivity is derived from the HfNCl layer. We have shown the unambiguous evidence for the quasi-two-dimensional superconducting character in this system

Multiple splitting of G-band modes from individual multiwalled carbon nanotubes

Surface-enhanced Raman scattering spectra of an individual multiwalled carbon nanotube (MWNT) with the innermost diameter ∼1nm, prepared by hydrogen arc discharge, show a single peak of radial breathing mode and multiple splitting of the tangential stretching G-band modes. Based on Lorentzian line shape analysis and related theoretical calculations, the G-band modes of MWNT are confirmed to be composed of both G-band modes (linewidth 4cm-1) from the innermost tube and graphite-like mode (linewidth ∼20cm -1) from the outer cylinders in MWNT. This observation indicates that MWNTs are unique and possess characteristic Raman spectra different from other sp2 carbon allotropes

Localization of hRad9 in breast cancer

<p>Abstract</p> <p>Background</p> <p><it>hRad9 </it>is a cell cycle checkpoint gene that is up-regulated in breast cancer. We have previously shown that the mRNA up-regulation correlated with tumor size and local recurrence. Immunohistochemical studies were made to better define the role of <it>hRad9 </it>in breast carcinogenesis.</p> <p>Methods</p> <p>Localisation of hRad9 protein were performed on paired tumor and normal breast tissues. Immunoblotting with and without dephosphorylation was used to define the protein isolated from breast cancer cells.</p> <p>Results</p> <p>Increased hRad9 protein was observed in breast cancer cells nucleus compared to non-tumor epithelium. This nuclear protein existed in hyperphosphorylated forms which may be those of the hRad9-hRad1-hHus1 complex.</p> <p>Conclusion</p> <p>Finding of hyperphosphorylated forms of hRad9 in the nucleus of cancer cells is in keeping with its function in ameliorating DNA instability, whereby it inadvertently assists tumor growth.</p

Role of dynamic Jahn-Teller distortions in Na2C60 and Na2CsC60 studied by NMR

Through 13C NMR spin lattice relaxation (T1) measurements in cubic Na2C60, we detect a gap in its electronic excitations, similar to that observed in tetragonal A4C60. This establishes that Jahn-Teller distortions (JTD) and strong electronic correlations must be considered to understand the behaviour of even electron systems, regardless of the structure. Furthermore, in metallic Na2CsC60, a similar contribution to T1 is also detected for 13C and 133Cs NMR, implying the occurence of excitations typical of JT distorted C60^{2-} (or equivalently C60^{4-}). This supports the idea that dynamic JTD can induce attractive electronic interactions in odd electron systems.Comment: 3 figure

Analysis of 13C-NMR spectra in C60 superconductors : Hyperfine coupling constants, electronic correlation effect, and magnetic penetration depth

A 13C-NMR anisotropic hyperfine coupling tensor was determined as 2π(-1.68, -1.68, 3.37)×106 rad/sec for C603- in A3C60 superconductors, where A is an alkali metal, by analyzing 13C-NMR spectra below 85 K. Combined with an isotropic coupling constant of (2π×0.69)×106 rad/sec, the 2s and 2p characters of the electronic wave functions at the Fermi level were deduced. The results were compatible with local-density-approximation band calculations. From a simulation of 13C-NMR spectra at superconducting state, the traceless chemical (orbital) shift tensor and isotropic chemical shift were determined as (67, 34, -101) ppm and ∼150 ppm, respectively. An estimated magnetic penetration depth is larger than 570 nm in K3C60. Furthermore, the modified Korringa relation, T1TK2∼βS (with Knight shift K, spin-lattice relaxation time T1, and Korringa constant S), clearly showed the existence of weak but substantial antiferromagnetic spin fluctuation in A3C60; β=0.40–0.58 with an error of ±20%.0 The Stoner enhancement factor was also determined as 1–1.5 from a comparison between spin susceptibility obtained from NMR and band-calculation results

Detection by NMR of a "local spin-gap" in quenched CsC60

We present a 13C and 133Cs NMR investigation of the CsC60 cubic quenched phase. Previous ESR measurements suggest that this phase is metallic, but NMR reveals contrasting electronic behavior on the local scale. The 13C spin-lattice relaxation time (T1) exhibits a typical metallic behavior down to 50 K, but indicates that a partial spin-gap opens for T<50 K. Unexpectedly, 133Cs NMR shows that there are two inequivalent Cs sites. For one of these sites, the NMR shift and (T1T)^{-1} follow an activated law, confirming the existence of a spin-gap. We ascribe this spin-gap to the occurrence of localized spin-singlets on a small fraction of the C60 molecules.Comment: 4 figure

Gaps and excitations in fullerides with partially filled bands : NMR study of Na2C60 and K4C60

We present an NMR study of Na2C60 and K4C60, two compounds that are related by electron-hole symmetry in the C60 triply degenerate conduction band. In both systems, it is known that NMR spin-lattice relaxation rate (1/T1) measurements detect a gap in the electronic structure, most likely related to singlet-triplet excitations of the Jahn-Teller distorted (JTD) C60^{2-} or C60^{4-}. However, the extended temperature range of the measurements presented here (10 K to 700 K) allows to reveal deviations with respect to this general trend, both at high and low temperatures. Above room temperature, 1/T1 deviates from the activated law that one would expect from the presence of the gap and saturates. In the same temperature range, a lowering of symmetry is detected in Na2C60 by the appearance of quadrupole effects on the 23Na spectra. In K4C60, modifications of the 13C spectra lineshapes also indicate a structural modification. We discuss this high temperature deviation in terms of a coupling between JTD and local symmetry. At low temperatures, 1/T$_1$T tends to a constant value for Na2C60, both for 13C and 23Na NMR. This indicates a residual metallic character, which emphasizes the proximity of metallic and insulting behaviors in alkali fullerides.Comment: 12 pages, 13 figure

Proton relaxation in the superconducting organic solid (BEDT-TTF)2Cu(NCS)2: evidence for relaxation by localized paramagnetic centers

The nonexponential character of the build-up of the nuclear magnetization usually increases on lowering the temperature. Superconducting fluctuations have been offered in a speculative way as an explanation for the nonexponential spin relaxation. We have observed the same relaxation behaviour in our investigation of the proton spin relaxation in (BEDT-TTF)2Cu(NCS)2 which is an organic conductor at room temperature and becomes a superconductor at Tc=10.4 K at ambient pressure. As we noticed during preliminary measurements that the degree of deviation from exponential relaxation depends on the sample under study we decided to do experiments under controlled conditions of sample preparation