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Homogeneous ZnTPyP/WO3 nanorod-on-nanorod Z-scheme photocatalysts are prepared for an enhanced photocatalytic hydrogen generation. This study offers valuable information for preparing organic–inorganic direct Z-scheme photocatalysts.

The self-assembly of optically active building blocks into functional nanocrystals as high-activity photocatalysts is a key in the field of photocatalysis. Cobalt porphyrin with abundant catalytic properties is extensively studied in photocatalytic water oxidation and CO2 reduction. Here, we present the fabrication of cobalt porphyrin nanocrystals through a surfactant-assisted interfacial self-assembly process using Co-tetra(4-pyridyl) porphyrin as building block. The self-assembly process relies on the combined noncovalent interactions such as π-π stacking and axial Co-N coordination between individual porphyrin molecules within surfactant micelles. Tuning different reaction conditions (temperature, the ratio of co-solvent DMF) and types of surfactant, various nanocrystals with well-defined 1D to 3D morphologies such as nanowires, nanorods and nano hexagonal prism were obtained. Due to the ordered accumulation of molecules, the nanocrystals exhibit the properties of the enhanced capability of visible light capture and can conduce to improve the transport and separation efficiency of the photogenerated carriers, which is important for photocatalysis. Further studies of photocatalytic CO2 reduction are being performed to address the relationship between the size and shape of the nanocrystals with the photocatalytic activity.

Nanoparticle photosensitizers possess technical advantages for photocatalytic reactions due to enhanced light harvesting and efficient charge transport. Here we report synthesis of semiconductor nanoparticles through covalent coupling and assembly of metalloporphyrin with condensed carbon nitride. The resultant nanoparticles consist of light harvesting component from the condensed carbon nitride and photocatalytic sites from the metalloporphyrins. This synergetic particle system effectively initiates efficient charge separation and transport and exhibits excellent photocatalytic activity for CO2 reduction. The CO production rate can reach up to 57 µmol/(gh) with a selectivity of 79% over competing H2 evolution. Controlled experiments demonstrate that the combination of light harvesting with photocatalytic activity via covalent assembly is crucial for the high photocatalytic activity. Due to effective charge separation and transfer, the resultant nanoparticle photocatalysts show exceptional photo stability against photo-corrosion under light irradiation, enabling for long-term utilization. This research opens a new way for the development of stable, effective nanoparticle photocatalysts using naturally abundant porphyrin pigments.

Author(s): He, Y; Chen, SD; Li, ZX; Zhao, D; Song, D; Yoshida, Y; Eisaki, H; Wu, T; Chen, XH; Lu, DH; Meingast, C; Devereaux, TP; Birgeneau, RJ; Hashimoto, M; Lee, DH; Shen, ZX | Abstract: Fluctuating superconductivity—vestigial Cooper pairing in the resistive state of a material—is usually associated with low dimensionality, strong disorder, or low carrier density. Here, we report single-particle spectroscopic, thermodynamic and magnetic evidence for persistent superconducting fluctuations in the heavily hole-doped cuprate superconductor () despite the high carrier density. With a sign-problem-free quantum MontenCarlo calculation, we show how a partially flat band at can help enhance superconducting phase fluctuations. Finally, we discuss the implications of an anisotropic band structure on the phase-coherence-limited superconductivity in overdoped cuprates and other superconductors.

In order to broaden the absorption range of graphitic carbon nitride, one of the common methods is to couple the well-known photosensitizer porphyrin with graphitic carbon nitride through van der Waals weak interactions. To date, to combine porphyrin with graphitic carbon nitride through covalent interactions has not been settled. In this work, through rational molecular design, we successfully incorporated porphyrin into the matrixes of graphitic carbon nitride by covalent bonding via one-pot thermal copolymerization. The resultant material not only can widen the absorption range but also possess the enlarged specific surface area and construction intramolecular heterojunctions which can contribute to improve electron-holes separation efficiency. The resultant photocatalyst exhibited enhanced H2 production rate (7.6 mmol·g−1·h−1) and with the apparent quantum efficiency (AQE) of 13.3% at 450 nm. At the same time, this method opens a way to fabricate graphitic carbon nitride nanosheets via bottom-up strategy.

Author(s): Pfau, H; Chen, SD; Hashimoto, M; Gauthier, N; Rotundu, CR; Palmstrom, JC; Fisher, IR; Mo, SK; Shen, ZX; Lu, D | Abstract: The hallmark of nematic order in iron-based superconductors is a resistivity anisotropy but it is unclear to which extent quasiparticle dispersions, lifetimes, and coherence contribute. While the lifted degeneracy of the Fe dxz and dyz dispersions has been studied extensively, only little is known about the two other factors. Here, we combine in situ strain tuning with ARPES and study the nematic response of the spectral weight in BaFe2As2. The symmetry analysis of the ARPES spectra demonstrates that the dxz band gains quasiparticle spectral weight compared to the dyz band for negative antisymmetric strain Δϵyy suggesting the same response inside the nematic phase. Our results are compatible with a different coherence of the dxz and dyz orbital within a Hund's metal picture. We also discuss the influence of orbital mixing.

Significance Fermi surface (FS) topology is a fundamental property of metals and superconductors. In electron-doped cuprate Nd 2− x Ce x CuO 4 , an unexpected FS reconstruction has been observed in optimal- and overdoped regime ( x = 0.15 − 0.17) by quantum oscillation measurements (QOM). This is puzzling because neutron scattering suggests that the antiferromagnetic long-range order, which is believed to reconstruct the FS, vanishes before x = 0.14. Here, we report angle-resolved photoemission evidence of FS reconstruction. The observed FSs are in quantitative agreement with QOM, suggesting an intrinsic FS reconstruction without field. Furthermore, the energy gap of the reconstruction decreases rapidly near x = 0.17 like an order parameter, echoing the quantum critical doping in transport. The totality of the data points to a mysterious order between x = 0.14 and 0.17.

Ultrahigh-resolution resonant inelastic X-ray scattering shows how dispersive charge density wave excitations influence the charge and lattice degrees of freedom in a high-Tc cuprate, pointing to a connection to the mysterious pseudogap state. Experimental evidence on high-Tc cuprates reveals ubiquitous charge density wave (CDW) modulations1,2,3,4,5,6,7,8,9,10, which coexist with superconductivity. Although the CDW had been predicted by theory11,12,13, important questions remain about the extent to which the CDW influences lattice and charge degrees of freedom and its characteristics as functions of doping and temperature. These questions are intimately connected to the origin of the CDW and its relation to the mysterious cuprate pseudogap10,14. Here, we use ultrahigh-resolution resonant inelastic X-ray scattering to reveal new CDW character in underdoped Bi2.2Sr1.8Ca0.8Dy0.2Cu2O8+δ. At low temperature, we observe dispersive excitations from an incommensurate CDW that induces anomalously enhanced phonon intensity, unseen using other techniques. Near the pseudogap temperature T∗, the CDW persists, but the associated excitations significantly weaken with an indication of CDW wavevector shift. The dispersive CDW excitations, phonon anomaly, and analysis of the CDW wavevector provide a comprehensive momentum-space picture of complex CDW behaviour and point to a closer relationship with the pseudogap state.

A sharp boundary in the cuprates Many physicists working on cuprate superconductors believe that the so-called strange metal phase in the cuprate phase diagram is associated with a quantum critical point. Within this picture, the quantum critical point gives rise to a V-shaped region in the doping-temperature phase diagram of the cuprates: the strange metal phase. Chen et al. used angle-resolved photoemission spectroscopy in the cuprate family Bi2212 to challenge this view. By taking comprehensive measurements as a function of doping and temperature—and making sure that the signal was not affected by environmental conditions—they found an incoherent strange metal phase that was sharply separated from a conventional phase by a temperature-independent vertical line in the phase diagram. Science , this issue p. 1099

The momentum dependence of the nematic order parameter is an important ingredient in the microscopic description of iron-based high-temperature superconductors. While recent reports on FeSe indicate that the nematic order parameter changes sign between electron and hole bands, detailed knowledge is still missing for other compounds. Combining angle-resolved photoemission spectroscopy (ARPES) with uniaxial strain tuning, we measure the nematic band splitting in both FeSe and BaFe$_2$As$_2$ without interference from either twinning or magnetic order. We find that the nematic order parameter exhibits the same momentum dependence in both compounds with a sign change between the Brillouin center and the corner. This suggests that the same microscopic mechanism drives the nematic order in spite of the very different phase diagrams., Comment: 7 pages, 4 figures

The superconducting dome of most iron-based superconductors emerges from a phase with nematic and magnetic ordering. However, the multiband and multiorbital nature of iron-based superconductors as well as twinning effects pose challenges to fully characterize the implications of these two ordering phenomena for the band structure. Here, the authors report high-quality ARPES measurements on twinned and detwinned BaFe${}_{2}$As${}_{2}$ and present a comprehensive and systematic overview of the band structure in the normal and the magnetically ordered states of this prototype parent compound.

Conspiring interactions in a cuprate More than 30 years after the discovery of high-temperature superconductivity in copper oxides, its mechanism remains a mystery. Electron pairing mediated solely by lattice vibrations—phonons—is thought to be insufficient to account for the high transition temperatures. He et al. found a rapid and correlated increase of the superconducting gap and electron-phonon interactions as the chemical composition of their bismuth-based cuprate samples was varied across a critical doping concentration. The interplay of electron-phonon with electron-electron interactions may lead to enhanced transition temperatures. Science , this issue p. 62

The origin of the large thermopower in ${\mathrm{Na}}_{x}{\mathrm{CoO}}_{2}$ is complicated by correlation phenomena. To disentangle the effects from multiple interactions, we use angle-resolved photoemission to study ${\mathrm{K}}_{x}{\mathrm{RhO}}_{2}$, an isostructural analogy of ${\mathrm{Na}}_{x}{\mathrm{CoO}}_{2}$ with large thermopower and weak electron correlation. Using the experimentally measured electronic structure, we demonstrate that the thermopower in ${\mathrm{K}}_{x}{\mathrm{RhO}}_{2}$ can be quantitatively explained within the quasiparticle framework after including an electron-phonon mass enhancement effect. Extending the analysis to the cobaltate, we find the doubling in thermopower is well accounted for by additional band renormalization from electron correlation. As such, the large thermopower emerges from the itinerant quasiparticles dressed by hierarchical electron-phonon and electron-electron interactions.

© 2016 American Physical Society. An extreme magnetoresistance (XMR) has recently been observed in several nonmagnetic semimetals. Increasing experimental and theoretical evidence indicates that the XMR can be driven by either topological protection or electron-hole compensation. Here, by investigating the electronic structure of a XMR material, YSb, we present spectroscopic evidence for a special case which lacks topological protection and perfect electron-hole compensation. Further investigations reveal that a cooperative action of a substantial difference between electron and hole mobility and a moderate carrier compensation might contribute to the XMR in YSb.

An organic–inorganic hybrid paratungstate [enH2]2[Cu(en)2]3[H2W12O42]·6H2O (1) (en = ethylenediamine) has been hydrothermally synthesized by reaction of Na2WO4·2H2O with CuCl2·2H2O in the presence of en and structurally characterized by elemental analyses, IR spectroscopy, UV spectrum, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and X-ray single-crystal diffraction. It is worth pointing out that 1 exhibits the 6-connected 3-D framework with the long topological (O'Keeffe) vertex symbol 4·4·64·4·4·4·4·64·4·4·4·64·4·4·4 for the [Cu(en)2]3[H2W12O42]4 − node, which gives the short vertex (Schlafli) symbol of 41263. To the best of our knowledge, such 6-connected 3-D open-framework constructed from paratungstate clusters is for the first time observed in polyoxometalate chemistry.

The ${122}^{\ensuremath{\star}}$ series of iron chalcogenide superconductors, for example ${\mathrm{K}}_{x}{\mathrm{Fe}}_{2\ensuremath{-}y}{\mathrm{Se}}_{2}$, only possesses electron Fermi pockets. Their distinctive electronic structure challenges the picture built upon iron pnictide superconductors, where both electron and hole Fermi pockets coexist. However, partly due to the intrinsic phase separation in this family of compounds, many aspects of their behavior remain elusive. In particular, the evolution of the ${122}^{\ensuremath{\star}}$ series of iron chalcogenides with chemical substitution still lacks a microscopic and unified interpretation. Using angle-resolved photoemission spectroscopy, we studied a major fraction of ${122}^{\ensuremath{\star}}$ iron chalcogenides, including the isovalently ``doped'' ${\mathrm{K}}_{x}{\mathrm{Fe}}_{2\ensuremath{-}y}{\mathrm{Se}}_{2\ensuremath{-}z}{\mathrm{S}}_{z},{\mathrm{Rb}}_{x}{\mathrm{Fe}}_{2\ensuremath{-}y}{\mathrm{Se}}_{2\ensuremath{-}z}{\mathrm{Te}}_{z}$, and ${(\text{Tl},\mathrm{K})}_{x}{\mathrm{Fe}}_{2\ensuremath{-}y}{\mathrm{Se}}_{2\ensuremath{-}z}{\mathrm{S}}_{z}$. We found that the bandwidths of the low energy Fe $3d$ bands in these materials depend on doping; and more crucially, as the bandwidth decreases, the ground state evolves from a metal to a superconductor, and eventually to an insulator, yet the Fermi surface in the metallic phases is unaffected by the isovalent dopants. Moreover, the correlation-driven insulator found here with small band filling may be a novel insulating phase. Our study shows that almost all the known ${122}^{\ensuremath{\star}}\text{-series}$ iron chalcogenides can be understood via one unifying phase diagram which implies that moderate correlation strength is beneficial for the superconductivity.

We report the electronic structure of YbB6, a recently predicted moderately correlated topological insulator, measured by angle-resolved photoemission spectroscopy. We directly observed linearly dispersive bands around the time-reversal invariant momenta {\Gamma} and X with negligible kz dependence, consistent with odd number of surface states crossing the Fermi level in a Z2 topological insulator. Circular dichroism photoemission spectra suggest that these in-gap states possess chirality of orbital angular momentum, which is related to the chiral spin texture, further indicative of their topological nature. The observed insulating gap of YbB6 is about 100 meV, larger than that reported by theoretical calculations. Our results present strong evidence that YbB6 is a correlated topological insulator and provide a foundation for further studies of this promising material., Comment: 5 pages, 4 figures

The title compound is hydrothermally synthesized from a mixture of CuCl2, Na2WO4, en, AcOH, and H2O (pH 8.5, 100 °C, autoclave, 7 d; 25% yield).

© 2016 AIP Publishing LLC. We developed a table-top vacuum ultraviolet (VUV) laser with 113.778 nm wavelength (10.897 eV) and demonstrated its viability as a photon source for high resolution angle-resolved photoemission spectroscopy (ARPES). This sub-nanosecond pulsed VUV laser operates at a repetition rate of 10 MHz, provides a flux of 2 × 1012photons/s, and enables photoemission with energy and momentum resolutions better than 2 meV and 0.012 Å-1, respectively. Space-charge induced energy shifts and spectral broadenings can be reduced below 2 meV. The setup reaches electron momenta up to 1.2 Å-1, granting full access to the first Brillouin zone of most materials. Control over the linear polarization, repetition rate, and photon flux of the VUV source facilitates ARPES investigations of a broad range of quantum materials, bridging the application gap between contemporary low energy laser-based ARPES and synchrotron-based ARPES. We describe the principles and operational characteristics of this source and showcase its performance for rare earth metal tritellurides, high temperature cuprate superconductors, and iron-based superconductors.