We report a systematic angle-resolved photoemission study on NaxCoO2 for a wide range of Na concentrations (0.3 ≤ x ≤ 0.72). In all the metallic samples at different x, we observed (i) only a single hole-like Fermi surface centered around Γ and (ii) its area changes with x according to the Luttinger theorem. We also observed a surface state that exhibits a larger Fermi surface area. The e ′ g band and the associated small Fermi surface pockets near the K points predicted by band calculations are found to "sink" below the Fermi energy in a manner almost independent of the doping and temperature.The surprising discovery of superconductivity on Na x CoO 2 · yH 2 O [1] raises many interesting questions on the nature of pairing and its connection to the high-T c superconductivity. The phase diagram of the cobaltate Na x CoO 2 · yH 2 O, with varying electron doping x and water intercalation y over a wide range, is very rich and complicated. In addition to superconductivity, it exhibits charge order, magnetic order including a metamagnetic transition, and other structural transitions [2,3,4,5]. The physics of these phases and the transitions among them is of importance by itself, and offers an excellent platform for studying correlated triangular lattice fermion systems.Understanding the evolution of the low-energy electronic structure such as the quasiparticle (QP) dispersion and the Fermi surface (FS) topology is a necessary step toward understanding the diverse physical properties and the nature of the pairing interaction in this class of transition metal oxide. It is therefore important to gain the precise knowledge of the FS structure and the low-energy excitations in the unhydrated Na x CoO 2 which have been the focus in many recent theoretical and experimental efforts. The cobaltate is a multi-orbital system where the Co 4+ is in the 3d 5 configuration, occupying the lower t 2g band complex similar to the ruthenate Sr 2 RuO 4 . First principle band calculations have predicted that Na x CoO 2 has a large FS associated with the a 1g band centered around the Γ point and six small FS pockets of mostly e ′ g character near the K points for a wide range of x [6,7]. Based on this band structure, it has been proposed that the large density of states contribution from the six FS pockets and the nesting condition among them enhance the spin fluctuations and lead to superconducting pairing of the QPs on these FSs [8]. However, angle-resolved photoelectron spectroscopy (ARPES) measurements on the cobaltate with high Na concentrations (x ∼ 0.6 -0.7) revealed only the large FS [9,10]. It was also noticed that the enclosed FS area, i.e. the density of holes, may not satisfy the Luttinger theorem which is a fundamental QP counting rule in interacting electron systems. It is therefore desirable to study the evolution of the QP band dispersion and the FS, especially the fate of the FS pockets as a function of the Na concentration x. This is the focus of this work. We choose a set of metallic Na x CoO 2 with 0.3 ≤ x ≤ 0.72. The in...
The electronic structure of single crystals Na0.6CoO2, which are closely related to the superconducting Na0.3CoO2.yH2O (Tc ∼ 5K), is studied by angle-resolved photoelectron spectroscopy. While the measured Fermi surface is found to be consistent with the prediction of a local density band theory, the energy dispersion is highly renormalized, with an anisotropy along the two principle axes (Γ-K, Γ-M ). Our ARPES result also indicates that an extended flat band is formed slightly above EF along Γ-K. In addition, an unusual band splitting is observed in the vicinity of the Fermi surface along the Γ-M direction, which differs from the predicted bilayer splitting.
We report angle-resolved photoelectron spectroscopy results of the Fermi surface of Ca1.5Sr0.5RuO4, which is at the boundary of magnetic/orbital instability in the phase diagram of the Ca-substituted Sr ruthenates. Three t(2g) energy bands and the corresponding Fermi surface sheets are observed, which are also present in the Ca-free Sr2RuO4. We find that while the Fermi surface topology of the alpha,beta (d(yz,zx)) sheets remains almost the same in these two materials, the gamma (d(xy)) sheet exhibits a holelike Fermi surface in Ca1.5Sr0.5RuO4 in contrast to being electronlike in Sr2RuO4. Our observation of all three volume conserving Fermi surface sheets clearly demonstrates the absence of orbital-selective Mott transition, which was proposed theoretically to explain the unusual transport and magnetic properties in Ca1.5Sr0.5RuO4.
This study explored the influence of long non-coding RNA (lncRNA) SNHG14 on α-synuclein (α-syn) expression and Parkinson’s disease (PD) pathogenesis. Firstly, we found that the expression level of SNHG14 was elevated in brain tissues of PD mice. In MN9D cells, the rotenone treatment (1μmol/L) enhanced the binding between transcriptional factor SP-1 and SNHG14 promoter, thus promoting SNHG14 expression. Interference of SNHG14 ameliorated the DA neuron injury induced by rotenone. Next, we found an interaction between SNHG14 and miR-133b. Further study showed that miR-133b down-regulated α-syn expression by targeting its 3’-UTR of mRNA and SNHG14 could reverse the negative effect of miR-133b on α-syn expression. Interference of SNHG14 reduced rotenone-induced DA neuron damage through miR-133b in MN9D cells and α-syn was responsible for the protective effect of miR-133b. Similarly, interference of SNHG14 mitigated neuron injury in PD mouse model. All in all, silence of SNHG14 mitigates dopaminergic neuron injury by down-regulating α-syn via targeting miR-133b, which contributes to improving PD.
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