Electronic structure near the 1/8-anomaly in La-based cuprates

We report an angle resolved photoemission study of the electronic structure of the pseudogap state in \NdLSCO ($T_c<7$ K). Two opposite dispersing Fermi arcs are the main result of this study. The several scenarios that can explain this observation are discussed.Comment: A high-resolution version can be found at http://lns.web.psi.ch/lns/download/Pockets/arXiv.pd

Nodal Landau Fermi-Liquid Quasiparticles in Overdoped La1.77_{1.77}Sr0.23_{0.23}CuO4_4

Nodal angle resolved photoemission spectra taken on overdoped La$_{1.77}$Sr$_{0.23}$CuO$_4$ are presented and analyzed. It is proven that the low-energy excitations are true Landau Fermi-liquid quasiparticles. We show that momentum and energy distribution curves can be analyzed self-consistently without quantitative knowledge of the bare band dispersion. Finally, by imposing Kramers-Kronig consistency on the self-energy $\Sigma$, insight into the quasiparticle residue is gained. We conclude by comparing our results to quasiparticle properties extracted from thermodynamic, magneto-resistance, and high-field quantum oscillation experiments on overdoped Tl$_2$Ba$_2$CuO$_{6+\delta}$.Comment: Accepted for publication in Phys. Rev.

The coherent {\it d}-wave superconducting gap in underdoped La2−x_{2-x}Srx_{x}CuO4_4 as studied by angle-resolved photoemission

We present angle-resolved photoemission spectroscopy (ARPES) data on moderately underdoped La$_{1.855}$Sr$_{0.145}$CuO$_4$ at temperatures below and above the superconducting transition temperature. Unlike previous studies of this material, we observe sharp spectral peaks along the entire underlying Fermi surface in the superconducting state. These peaks trace out an energy gap that follows a simple {\it d}-wave form, with a maximum superconducting gap of 14 meV. Our results are consistent with a single gap picture for the cuprates. Furthermore our data on the even more underdoped sample La$_{1.895}$Sr$_{0.105}$CuO$_4$ also show sharp spectral peaks, even at the antinode, with a maximum superconducting gap of 26 meV.Comment: Accepted by Phys. Rev. Let

Spectroscopic evidence for preformed Cooper pairs in the pseudogap phase of cuprates

Angle-resolved photoemission on underdoped La$_{1.895}$Sr$_{0.105}$CuO$_4$ reveals that in the pseudogap phase, the dispersion has two branches located above and below the Fermi level with a minimum at the Fermi momentum. This is characteristic of the Bogoliubov dispersion in the superconducting state. We also observe that the superconducting and pseudogaps have the same d-wave form with the same amplitude. Our observations provide direct evidence for preformed Cooper pairs, implying that the pseudogap phase is a precursor to superconductivity

Proximity ligation assay reveals both pre- A nd postsynaptic localization of the APP-processing enzymes ADAM10 and BACE1 in rat and human adult brain

Background: Synaptic degeneration and accumulation of amyloid \u3b2-peptides (A\u3b2) are hallmarks of the Alzheimer diseased brain. A\u3b2 is synaptotoxic and produced by sequential cleavage of the amyloid precursor protein (APP) by the \u3b2-secretase BACE1 and by \u3b3-secretase. If APP is instead cleaved by the \u3b1-secretase ADAM10, A\u3b2 will not be generated. Although BACE1 is considered to be a presynaptic protein and ADAM10 has been reported to mainly localize to the postsynaptic density, we have previously shown that both ADAM10 and BACE1 are highly enriched in synaptic vesicles of rat brain and mouse primary hippocampal neurons. Results: Here, using brightfield proximity ligation assay, we expanded our previous result in primary neurons and investigated the in situ synaptic localization of ADAM10 and BACE1 in rat and human adult brain using both pre- A nd postsynaptic markers. We found that ADAM10 and BACE1 were in close proximity with both the presynaptic marker synaptophysin and the postsynaptic marker PSD-95. The substrate APP was also detected both pre- A nd postsynaptically. Subcellular fractionation confirmed that ADAM10 and BACE1 are enriched to a similar degree in synaptic vesicles and as well as in the postsynaptic density. Conclusions: We show that the \u3b1-secretase ADAM10 and the \u3b2-secretase BACE1 are located in both the pre- A nd postsynaptic compartments in intact brain sections. These findings increase our understanding of the regulation of APP processing, thereby facilitating development of more specific treatment strategies

Topological crystalline insulator states in Pb(1-x)Sn(x)Se

Topological insulators are a novel class of quantum materials in which time-reversal symmetry, relativistic (spin-orbit) effects and an inverted band structure result in electronic metallic states on the surfaces of bulk crystals. These helical states exhibit a Dirac-like energy dispersion across the bulk bandgap, and they are topologically protected. Recent theoretical proposals have suggested the existence of topological crystalline insulators, a novel class of topological insulators in which crystalline symmetry replaces the role of time-reversal symmetry in topological protection [1,2]. In this study, we show that the narrow-gap semiconductor Pb(1-x)Sn(x)Se is a topological crystalline insulator for x=0.23. Temperature-dependent magnetotransport measurements and angle-resolved photoelectron spectroscopy demonstrate that the material undergoes a temperature-driven topological phase transition from a trivial insulator to a topological crystalline insulator. These experimental findings add a new class to the family of topological insulators. We expect these results to be the beginning of both a considerable body of additional research on topological crystalline insulators as well as detailed studies of topological phase transitions.Comment: v2: published revised manuscript (6 pages, 3 figures) and supplementary information (5 pages, 8 figures

Density-Induced Breaking of Pairs in the Attractive Hubbard Model

A conserving T-matrix approximation is applied to the two-dimensional attractive Hubbard model in the low-density regime. A set of self-consistent equations is solved in the real-frequency domain to avoid the analytic continuation procedure. By tuning the chemical potential the particle density was varied in the limits 0.01 < n < 0.18. For the value of the attractive potential U=8t the binding energy of pairs monotonically decreases with increasing n, from its zero-density limit 2.3t and vanishes at a critical density n=0.19. A pairing-induced pseudogap in the single-particle density of states is found at low densities and temperatures.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Let