We present a soft x-ray angle-resolved photoemission spectroscopy study of overdoped high-temperature superconductors. In-plane and out-of-plane components of the Fermi surface are mapped by varying the photoemission angle and the incident photon energy. No k_{z} dispersion is observed along the nodal direction, whereas a significant antinodal k_{z} dispersion is identified for La-based cuprates. Based on a tight-binding parametrization, we discuss the implications for the density of states near the van Hove singularity. Our results suggest that the large electronic specific heat found in overdoped La_{2-x}Sr_{x}CuO_{4} cannot be assigned to the van Hove singularity alone. We therefore propose quantum criticality induced by a collapsing pseudogap phase as a plausible explanation for observed enhancement of electronic specific heat.

Human Cellular Retinol Binding Protein II (hCRBPII), a member of the intracellular Lipid binding protein family, is a monomeric protein responsible for the intracellular transport of retinol and retinal. Herein we report that hCRBPII forms an extensive domain swapped dimer during bacterial expression. The domain swapped region encompasses almost half of the protein. The dimer represents a novel structural architecture with the mouths of the two binding cavities facing each other, producing a new binding cavity that spans the length of the protein complex. Though wild-type hCRBPII forms the dimer, the propensity for dimerization can be substantially increased via mutation at Tyr60. The monomeric form of the wild type protein represents the thermodynamically more stable species, making the domain swapped dimer a kinetically trapped entity. Hypothetically, the wild type protein has evolved to minimize dimerization of the folding intermediate through a critical hydrogen bond (Tyr60-Glu72) that disfavors the dimeric form.

Electronic band structures in solids stem from a periodic potential reflecting the structure of either the crystal lattice or electronic order. In the stoichiometric ruthenate Ca3Ru2O7, numerous Fermi surface-sensitive probes indicate a low-temperature electronic reconstruction. Yet, the causality and the reconstructed band structure remain unsolved. Here, we show by angle-resolved photoemission spectroscopy, how in Ca3Ru2O7 a C2-symmetric massive Dirac semimetal is realized through a Brillouin-zone preserving electronic reconstruction. This Dirac semimetal emerges in a two-stage transition upon cooling. The Dirac point and band velocities are consistent with constraints set by quantum oscillation, thermodynamic, and transport experiments, suggesting that the complete Fermi surface is resolved. The reconstructed structure—incompatible with translational-symmetry-breaking density waves—serves as an important test for band structure calculations of correlated electron systems.

Relativistic massless Dirac fermions can be probed with high-energy physics experiments, but appear also as low-energy quasi-particle excitations in electronic band structures. In condensed matter systems, their massless nature can be protected by crystal symmetries. Classification of such symmetry-protected relativistic band degeneracies has been fruitful, although many of the predicted quasi-particles still await their experimental discovery. Here we reveal, using angle-resolved photoemission spectroscopy, the existence of two-dimensional type-II Dirac fermions in the high-temperature superconductor La1.77Sr0.23CuO4. The Dirac point, constituting the crossing of and bands, is found approximately one electronvolt below the Fermi level (EF) and is protected by mirror symmetry. If spin-orbit coupling is considered, the Dirac point degeneracy is lifted and the bands acquire a topologically non-trivial character. In certain nickelate systems, band structure calculations suggest that the same type-II Dirac fermions can be realised near EF.

A comprehensive angle resolved photoemission spectroscopy study of the band structure in single layer cuprates is presented with the aim of uncovering universal trends across different materials. Five different hole-and electron-doped cuprate superconductors (La1.59Eu0.2Sr0.21CuO4, La1.77Sr0.23CuO4, Bi1.74Pb0.38Sr1.88CuO 6+δ , Tl2Ba2CuO 6+δ , and Pr1.15La0.7Ce0.15CuO4) have been studied with special focus on the bands with predominately d-orbital character. Using light polarization analysis, the eg and t2g bands are identified across these materials. A clear correlation between the d 3z 2 −r 2 band energy and the apical oxygen distance dA is demonstrated. Moreover, the compound dependence of the d x 2 −y 2 band bottom and the t2g band top is revealed. Direct comparison to density functional theory (DFT) calculations employing hybrid exchange-correlation functionals demonstrates excellent agreement. We thus conclude that the DFT methodology can be used to describe the global band structure of overdoped single layer cuprates on both the hole and electron doped side.Introduction: The physics of cuprate superconductors has been a subject of intense investigations for more than three decades [1-3]. Yet, some of the most fundamental questions related to high-temperature superconductivity remain open. For example, consensus on the mechanism underpinning cuprate superconductivity is still missing. Related to this is the question of the defining parameters for the transition temperature T c [4-9], and how to optimize it. Starting point for most theoretical approaches to superconductivity is an (effective) electronic band structure as well as the interactions that are relevant for driving a pairing mechanism. The former is typically obtained through density functional theory (DFT). However, because DFT cannot describe all relevant aspects of the electronic structure (such as the Mott insulating phase out of which superconductivity emerges upon hole or electron doping [10]) it is commonly viewed as too simplistic of an approach in the context of the cuprates [11]. Another widespread assumption is that effective models for cuprates can be constructed solely on the d x 2 −y 2 band structure. This latter assumption has recently been challenged [6,12] by angle-resolved photoemission spectroscopy (ARPES) observations of a second band (d 3z 2 −r 2 ) hybridizing with the d x 2 −y 2 orbital in overdoped La 1.77 Sr 0.23 CuO 4 (LSCO) [7,13].Here we provide a systematic ARPES and DFT study of the electronic d-band structure across single layer cuprate superconductors.Five different hole-and electron-overdoped superconducting systems [La 1.59 Eu 0.2 Sr 0.21 CuO 4 (Eu-LSCO), La 1.77 Sr 0.23 CuO 4 (LSCO), Bi 1.74 Pb 0.38 Sr 1.88 CuO 6+δ (Bi2201), Tl 2 Ba 2 CuO 6+δ (Tl2201), and Pr 1.15 La 0.7 Ce 0.15 CuO 4 (PLCCO)] have been investigated experimentally. This has led to three main observations: (i ) clear identification of the d 3z 2 −r 2 band position in three of the mentioned compounds, (ii ) compound dependence of the d x 2 −y 2 band b...