Electron Glass Phase with Resilient Zhang-Rice Singlets in LiCu_{3}O_{3}.

LiCu_{3}O_{3} is an antiferromagnetic mixed valence cuprate where trilayers of edge-sharing Cu(II)O (3d^{9}) are sandwiched in between planes of Cu(I) (3d^{10}) ions, with Li stochastically substituting Cu(II). Angle-resolved photoemission spectroscopy (ARPES) and density functional theory reveal two insulating electronic subsystems that are segregated in spite of sharing common oxygen atoms: a Cu d_{z^{2}}/O p_{z} derived valence band (VB) dispersing on the Cu(I) plane, and a Cu 3d_{x^{2}-y^{2}}/O 2p_{x,y} derived Zhang-Rice singlet (ZRS) band dispersing on the Cu(II)O planes. First-principle analysis shows the Li substitution to stabilize the insulating ground state, but only if antiferromagnetic correlations are present. Li further induces substitutional disorder and a 2D electron glass behavior in charge transport, reflected in a large 530 meV Coulomb gap and a linear suppression of VB spectral weight at E_{F} that is observed by ARPES. Surprisingly, the disorder leaves the Cu(II)-derived ZRS largely unaffected. This indicates a local segregation of Li and Cu atoms onto the two separate corner-sharing Cu(II)O_{2} sub-lattices of the edge-sharing Cu(II)O planes, and highlights the ubiquitous resilience of the entangled two hole ZRS entity against impurity scattering.

Radial Spin Texture of the Weyl Fermions in Chiral Tellurium.

Trigonal tellurium, a small-gap semiconductor with pronounced magneto-electric and magneto-optical responses, is among the simplest realizations of a chiral crystal. We have studied by spin- and angle-resolved photoelectron spectroscopy its unconventional electronic structure and unique spin texture. We identify Kramers-Weyl, composite, and accordionlike Weyl fermions, so far only predicted by theory, and show that the spin polarization is parallel to the wave vector along the lines in k space connecting high-symmetry points. Our results clarify the symmetries that enforce such spin texture in a chiral crystal, thus bringing new insight in the formation of a spin vectorial field more complex than the previously proposed hedgehog configuration. Our findings thus pave the way to a classification scheme for these exotic spin textures and their search in chiral crystals.

Light-Induced Renormalization of the Dirac Quasiparticles in the Nodal-Line Semimetal ZrSiSe.

In nodal-line semimetals, linearly dispersing states form Dirac loops in the reciprocal space with a high degree of electron-hole symmetry and a reduced density of states near the Fermi level. The result is reduced electronic screening and enhanced correlations between Dirac quasiparticles. Here we investigate the electronic structure of ZrSiSe, by combining time- and angle-resolved photoelectron spectroscopy with ab initio density functional theory (DFT) complemented by an extended Hubbard model (DFT+U+V) and by time-dependent DFT+U+V. We show that electronic correlations are reduced on an ultrashort timescale by optical excitation of high-energy electrons-hole pairs, which transiently screen the Coulomb interaction. Our findings demonstrate an all-optical method for engineering the band structure of a quantum material.

Evidence of Large Polarons in Photoemission Band Mapping of the Perovskite Semiconductor CsPbBr_{3}.

Lead-halide perovskite (LHP) semiconductors are emergent optoelectronic materials with outstanding transport properties which are not yet fully understood. We find signatures of large polaron formation in the electronic structure of the inorganic LHP CsPbBr_{3} by means of angle-resolved photoelectron spectroscopy. The experimental valence band dispersion shows a hole effective mass of 0.26±0.02 m_{e}, 50% heavier than the bare mass m_{0}=0.17 m_{e} predicted by density functional theory. Calculations of the electron-phonon coupling indicate that phonon dressing of the carriers mainly occurs via distortions of the Pb-Br bond with a Fröhlich coupling parameter α=1.81. A good agreement with our experimental data is obtained within the Feynman polaron model, validating a viable theoretical method to predict the carrier effective mass of LHPs ab initio.

The 'brick diet' and postprandial insulin: a practical method to balance carbohydrates ingested and prandial insulin to prevent hypoglycaemia in hospitalized persons with diabetes.

AIM: Insulin is the preferred treatment for the control of diabetes in hospital, but it raises the risk of hypoglycaemia, often because oral intake of carbohydrates in hospitalized persons is lower than planned. Our aim was to assess the effect on the incidence of hypoglycaemia of giving prandial insulin immediately after a meal depending on the amount of carbohydrate ingested. METHODS: A prospective pre-post intervention study in hospitalized persons with diabetes eating meals with stable doses of carbohydrates present in a few fixed foods. Foods were easily identifiable on the tray and contained fixed doses of carbohydrates that were easily quantifiable by nurses as multiples of 10 g (a 'brick'). Prandial insulin was given immediately after meals in proportion to the amount of carbohydrates eaten. RESULTS: In 83 of the first 100 people treated with the 'brick diet', the oral carbohydrate intake was lower than planned on at least one occasion (median: 3 times; Q1-Q3: 2-6 times) over a median of 5 days. Compared with the last 100 people treated with standard procedures, postprandial insulin given on the basis of ingested carbohydrate significantly reduced the incidence of hypoglycaemic events per day, from 0.11 ± 0.03 to 0.04 ± 0.02 (P < 0.001) with an adjusted incidence rate ratio of 0.70 (95% confidence interval 0.54-0.92; P = 0.011). CONCLUSIONS: In hospitalized persons with diabetes treated with subcutaneous insulin, the 'brick diet' offers a practical method to count the amount of carbohydrates ingested, which is often less than planned. Prandial insulin given immediately after a meal, in doses balanced with actual carbohydrate intake reduces the risk of hypoglycaemia.

Unveiling the electronic transformations in the semi-metallic correlated-electron transitional oxide Mo8O23.

Mo8O23 is a low-dimensional chemically robust transition metal oxide coming from a prospective family of functional materials, MoO3-x, ranging from a wide gap insulator (x = 0) to a metal (x = 1). The large number of stoichometric compounds with intermediate x have widely different properties. In Mo8O23, an unusual charge density wave transition has been suggested to occur above room temperature, but its low temperature behaviour is particularly enigmatic. We present a comprehensive experimental study of the electronic structure associated with various ordering phenomena in this compound, complemented by theory. Density-functional theory (DFT) calculations reveal a cross-over from a semi-metal with vanishing band overlap to narrow-gap semiconductor behaviour with decreasing temperature. A buried Dirac crossing at the zone boundary is confirmed by angle-resolved photoemission spectroscopy (ARPES). Tunnelling spectroscopy (STS) reveals a gradual gap opening corresponding to a metal-to-insulator transition at 343 K in resistivity, consistent with CDW formation and DFT results, but with large non-thermal smearing of the spectra implying strong carrier scattering. At low temperatures, the CDW picture is negated by the observation of a metallic Hall contribution, a non-trivial gap structure in STS below ∼170 K and ARPES spectra, that together represent evidence for the onset of the correlated state at 70 K and the rapid increase of gap size below ∼30 K. The intricate interplay between electronic correlations and the presence of multiple narrow bands near the Fermi level set the stage for metastability and suggest suitability for memristor applications.

Hallmarks of Hunds coupling in the Mott insulator Ca2RuO4.

A paradigmatic case of multi-band Mott physics including spin-orbit and Hund's coupling is realized in Ca2RuO4. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide-using angle-resolved photoemission electron spectroscopy-the band structure of the paramagnetic insulating phase of Ca2RuO4 and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund's coupling J=0.4 eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilization of the dxy orbital due to c-axis contraction is shown to be essential to explain the insulating phase. These results underscore the importance of multi-band physics, Coulomb interaction and Hund's coupling that together generate the Mott insulating state of Ca2RuO4.

Publisher's Note: Electronic Phase Separation and Dramatic Inverse Band Renormalization in the Mixed-Valence Cuprate LiCu_{2}O_{2} [Phys. Rev. Lett. 118, 176404 (2017)].

This corrects the article DOI: 10.1103/PhysRevLett.118.176404.

Electronic Phase Separation and Dramatic Inverse Band Renormalization in the Mixed-Valence Cuprate LiCu_{2}O_{2}.

We measured, by angle-resolved photoemission spectroscopy, the electronic structure of LiCu_{2}O_{2}, a mixed-valence cuprate where planes of Cu(I) (3d^{10}) ions are sandwiched between layers containing one-dimensional edge-sharing Cu(II) (3d^{9}) chains. We find that the Cu(I)- and Cu(II)-derived electronic states form separate electronic subsystems, in spite of being coupled by bridging O ions. The valence band, of the Cu(I) character, disperses within the charge-transfer gap of the strongly correlated Cu(II) states, displaying an unprecedented 250% broadening of the bandwidth with respect to the predictions of density functional theory. Our observation is at odds with the widely accepted tenet of many-body theory that correlation effects generally yield narrower bands and larger electron masses and suggests that present-day electronic structure techniques provide an intrinsically inappropriate description of ligand-to-d hybridizations in late transition metal oxides.

Strongly bound excitons in anatase TiO2 single crystals and nanoparticles.

Anatase TiO2 is among the most studied materials for light-energy conversion applications, but the nature of its fundamental charge excitations is still unknown. Yet it is crucial to establish whether light absorption creates uncorrelated electron-hole pairs or bound excitons and, in the latter case, to determine their character. Here, by combining steady-state angle-resolved photoemission spectroscopy and spectroscopic ellipsometry with state-of-the-art ab initio calculations, we demonstrate that the direct optical gap of single crystals is dominated by a strongly bound exciton rising over the continuum of indirect interband transitions. This exciton possesses an intermediate character between the Wannier-Mott and Frenkel regimes and displays a peculiar two-dimensional wavefunction in the three-dimensional lattice. The nature of the higher-energy excitations is also identified. The universal validity of our results is confirmed up to room temperature by observing the same elementary excitations in defect-rich samples (doped single crystals and nanoparticles) via ultrafast two-dimensional deep-ultraviolet spectroscopy.Here the authors combine steady-state angle-resolved photoemission spectroscopy, ellipsometry and ultrafast two-dimensional ultraviolet spectroscopy to examine the role of many-body correlations in anatase TiO2, revealing the existence of strongly bound excitons in single crystals and nanoparticles.

Ultrafast Optical Control of the Electronic Properties of ZrTe5.

We report on the temperature dependence of the ZrTe(5) electronic properties, studied at equilibrium and out of equilibrium, by means of time and angle resolved photoelectron spectroscopy. Our results unveil the dependence of the electronic band structure across the Fermi energy on the sample temperature. This finding is regarded as the dominant mechanism responsible for the anomalous resistivity observed at T*∼160 K along with the change of the charge carrier character from holelike to electronlike. Having addressed these long-lasting questions, we prove the possibility to control, at the ultrashort time scale, both the binding energy and the quasiparticle lifetime of the valence band. These experimental evidences pave the way for optically controlling the thermoelectric and magnetoelectric transport properties of ZrTe(5).

Interplay between electronic and structural properties in the Pb/Ag(1 0 0) interface.

We report an investigation of the structural and electronic properties of a Pb monolayer (ML) grown on Ag(1 0 0), by combining x-ray photoelectron diffraction (XPD) and angle resolved photoelectron spectroscopy (ARPES). The Pb atoms are found to arrange in a pseudo-hexagonal adlayer commensurate to the underlying square Ag substrate, resulting in a coincidence cell with c([Formula: see text]) periodicity. The electronic structure of the Pb ML in proximity of the Fermi level consists in three p-derived bands, which show different degrees of hybridization with the substrate for their different orbital characters. In particular, we report that the p xy states disperse without forming energy gap, in contrast to previous ARPES studies of the Pb ML on different metallic substrates. We attribute the absence of energy gap to the commensurability between substrate and adlayer, resulting in a higher two-dimensionality of the Pb ML.

Electron-Phonon Coupling in the Bulk of Anatase TiO2 Measured by Resonant Inelastic X-Ray Spectroscopy.

We investigate the polaronic ground state of anatase TiO2 by bulk-sensitive resonant inelastic x-ray spectroscopy (RIXS) at the Ti L3 edge. We find that the formation of the polaron cloud involves a single 95 meV phonon along the c axis, in addition to the 108 meV ab-plane mode previously identified by photoemission. The coupling strength to both modes is the same within error bars, and it is unaffected by the carrier density. These data establish RIXS as a directional bulk-sensitive probe of electron-phonon coupling in solids.

Momentum-resolved spin dynamics of bulk and surface excited States in the topological insulator Bi(2)Se(3).

The prospect of optically inducing and controlling a spin-polarized current in spintronic devices has generated wide interest in the out-of-equilibrium electronic and spin structure of topological insulators. In this Letter we show that only measuring the spin intensity signal over several orders of magnitude by spin-, time-, and angle-resolved photoemission spectroscopy can provide a comprehensive description of the optically excited electronic states in Bi_{2}Se_{3}. Our experiments reveal the existence of a surface resonance state in the second bulk band gap that is benchmarked by fully relativistic ab initio spin-resolved photoemission calculations. We propose that the newly reported state plays a major role in the ultrafast dynamics of the system, acting as a bottleneck for the interaction between the topologically protected surface state and the bulk conduction band. In fact, the spin-polarization dynamics in momentum space show that these states display macroscopically different temperatures and, more importantly, different cooling rates over several picoseconds.

Antisense transcription at the TRPM2 locus as a novel prognostic marker and therapeutic target in prostate cancer.

Overwhelming evidence indicates that cancer is a genetic disease caused by the accumulation of mutations in oncogenes and tumor suppressor genes. It is also increasingly apparent, however, that cancer depends not only on mutations in these coding genes but also on alterations in the large class of non-coding RNAs. Here, we report that one such long non-coding RNA, TRPM2-AS, an antisense transcript of TRPM2, which encodes an oxidative stress-activated ion channel, is overexpressed in prostate cancer (PCa). The high expression of TRPM2-AS and its related gene signature were found to be linked to poor clinical outcome, with the related gene signature working also independently of the patient's Gleason score. Mechanistically, TRPM2-AS knockdown led to PCa cell apoptosis, with a transcriptional profile that indicated an unbearable increase in cellular stress in the dying cells, which was coupled to cell cycle arrest, an increase in intracellular hydrogen peroxide and activation of the sense TRPM2 gene. Moreover, targets of existing drugs and treatments were found to be consistently associated with high TRPM2-AS levels in both targeted cells and patients, ultimately suggesting that the measurement of the expression levels of TRPM2-AS allows not only for the early identification of aggressive PCa tumors, but also identifies a subset of at-risk patients who would benefit from currently available, but mostly differently purposed, therapeutic agents.

Anisotropic softening of magnetic excitations along the nodal direction in superconducting cuprates.

The high-Tc cuprate superconductors are close to antiferromagnetic order. Recent measurements of magnetic excitations have reported an intriguing similarity to the spin waves--magnons--of the antiferromagnetic insulating parent compounds, suggesting that magnons may survive in damped, broadened form throughout the phase diagram. Here we show by resonant inelastic X-ray scattering on Bi(2)Sr(2)CaCu(2)O(8+δ) (Bi-2212) that the analogy with spin waves is only partial. The magnon-like features collapse along the nodal direction in momentum space and exhibit a photon energy dependence markedly different from the Mott-insulating case. These observations can be naturally described by the continuum of charge and spin excitations of correlated electrons. The persistence of damped magnons could favour scenarios for superconductivity built from quasiparticles coupled to spin fluctuations. However, excitation spectra composed of particle-hole excitations suggest that superconductivity emerges from a coherent treatment of electronic spin and charge in the form of quasiparticles with very strong magnetic correlations.

Angle-resolved photoemission spectroscopy of tetragonal CuO: evidence for intralayer coupling between cupratelike sublattices.

We investigate by angle-resolved photoemission the electronic structure of in situ grown tetragonal CuO, a synthetic quasi-two-dimensional edge-sharing cuprate. We show that, in spite of the very different nature of the copper oxide layers, with twice as many Cu in the CuO layers of tetragonal CuO as compared to the CuO(2) layers of the high-T(c) cuprates, the low-energy electronic excitations are surprisingly similar, with a Zhang-Rice singlet dispersing on weakly coupled cupratelike sublattices. This system should thus be considered as a member of the high-T(c) cuprate family, with, however, interesting differences due to the intralayer coupling between the cupratelike sublattices.

Nature of the bad metallic behavior of Fe1.06Te inferred from its evolution in the magnetic state.

We investigate with angle-resolved photoelectron spectroscopy the changes of the Fermi surface and the main bands from the paramagnetic state to the antiferromagnetic (AFM) state occurring below 72 K in Fe1.06Te. The evolution is completely different from that observed in Fe pnictides, as nesting is absent. The AFM state is a rather good metal, in agreement with our magnetic band structure calculation. On the other hand, the paramagnetic state is very anomalous with a large pseudogap of ~65 meV on the electron pocket that closes in the AFM state. We discuss this behavior in connection with spin fluctuations existing above the magnetic transition and the correlations predicted in the spin-freezing regime of the incoherent metallic state.

Opening of a Peierls gap in BaVS3 probed by V L3 edge resonant inelastic x-ray scattering.

V L3 edge resonant inelastic x-ray scattering measurements performed on high quality BaVS3 single crystals reveal that the intra-t2g dd excitations close to the elastic peak are suppressed below the metal-insulator transition induced by the Peierls instability. The depletion of electronic states close to the Fermi level represents a direct observation of the opening of a charge gap inside the t2g manifold.

Nonpareil Yb behavior in YbMn6Ge(6-x)Sn(x).

We investigate the temperature dependence of the Yb valence in YbMn6Ge1.8Sn4.2 and YbMn6Ge1.6Sn4.4 using resonant inelastic x-ray scattering experiments. Yb is found to be in an intermediate valent state in the whole investigated temperature range (10-450 K). We thus prove that the unusually high magnetic ordering temperature of Yb (∼60 and 90 K for x=4.2 and 4.4, respectively) involves an intermediate valent Yb, an unprecedentedly observed phenomenon. Further, an anomalous increase in the Yb valence is observed upon cooling. A scenario is proposed to explain this unusual behavior. It is based on the presence of magnetically ordered Mn moments and on an Anderson Hamiltonian with a Zeeman term modeling the magnetic interactions.