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.

The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates) materials remains heavily debated. Effective low-energy single-band models of the copper–oxygen orbitals are widely used because there exists no strong experimental evidence supporting multi-band structures. Here, we report angle-resolved photoelectron spectroscopy experiments on La-based cuprates that provide direct observation of a two-band structure. This electronic structure, qualitatively consistent with density functional theory, is parametrised by a two-orbital ( and ) tight-binding model. We quantify the orbital hybridisation which provides an explanation for the Fermi surface topology and the proximity of the van-Hove singularity to the Fermi level. Our analysis leads to a unification of electronic hopping parameters for single-layer cuprates and we conclude that hybridisation, restraining d-wave pairing, is an important optimisation element for superconductivity.

As a result of explorations into the solution chemistry of silver/gold mixtures, a unique diphosphine trimetallic chloronium dication was discovered that incorporates silver-arene chelation and a triangular mixed gold/silver core in the solid state. Notably, it was isolated from a Celite prefiltered solution initially thought to be silver-free. The crystal structure also incorporates the coordination to silver of one fluorine atom of one SbF6(-) counterion. The structure was compared to two new, but well-precedented, phosphine digold chloride cations. DFT calculations supported significant silver-halide and silver-arene interactions in the mixed gold/silver complex and metallophilic interactions in all three complexes. Comparison of computed data revealed that the ωB97X-D functional, which has a long-range corrected hybrid with atom-atom dispersion corrections, gave a better fit to the experimental data compared with the PBE0 functional, which has previously failed to capture aurophilic interactions. Preliminary studies support the presence of the mixed gold/silver structure in solution.

We present a comprehensive angle-resolved photoemission spectroscopy study of Ca1.8Sr0.2RuO4. Four distinct bands are revealed and along the Ru-O bond direction their orbital characters are identified through light polarisation analysis and comparison to dynamical mean field theory calculations. Bands assigned to dxz, dyz orbitals display Fermi liquid behavior with four-fold quasi particle mass renormalization. Extremely heavy Fermions -associated with a predominantly dxy band character -are shown to display non-Fermi liquid behavior. We thus demonstrate that Ca1.8Sr0.2RuO4 is a hybrid metal with an orbitally-selective Fermi liquid quasiparticle breakdown.Correlated metals are typically classified either as Fermi liquids or non-Fermi liquids depending on whether resistivity scales with temperature squared or not. There is, however, transport evidence suggesting that some materials are hybrids of these two metal classes [1]. This mixed regime is of particular interest as it provides insight into how Fermi liquids break down and the nature of non-Fermi liquid quasiparticles. In this context, multi-orbital metallic systems in conjunction with strong Hund's coupling and electron correlations are of great conceptual importance [2]. Such Hund's metals are expected to display orbital differentiated quasiparticle (QP) renormalization effects along with magnetic correlations [3]. In the strongly correlated limit, orbitally selective Mott physics (OSMP) has been explored theoretically [4][5][6][7][8][9]. The concepts of Hund's metals and OSMP have both been applied to describe band structure renormalization effects in pnictide superconductor compounds [10][11][12][13][14][15]. It remains, however, unclear whether these systems exhibit genuine heavy Fermion and Mott physics. In contrast, the oxide compounds LiV 2 O 4 and Ca 1.8 Sr 0.2 RuO 4 are multi-orbital systems where the existence of heavy Fermions are clearly demonstrated from specific heat measurements [16,17]. Ca 1.8 Sr 0.2 RuO 4 is furthermore in close proximity to a Mott-Hubbard metalinsulator transition [18]. Angle resolved-photoemission experiments (ARPES) on this system have been interpreted in terms of both the Hund's metal and the OSMP scenario [19,20]. Resistivity and specific heat indicate that the ground state is a Fermi liquid (FL). How-ever, a thermal excitation of just 1 K turns the system into a non-Fermi liquid (nFL) state [16]. Here we present a high-resolution ARPES study, demonstrating that Ca 1.8 Sr 0.2 RuO 4 is neither a standard Hunds metal nor representing OSMP. In fact, the thermally excited state constitutes an example of a hybrid metal. Along the Ru-O bond direction, bands with d xz , d yz orbital character display FL behavior whereas d xy dominated bands host nFL QPs. Breakdown of FL QPs are therefore orbitally selective. This physics might apply to other ruthenate systems such as for example Sr 3 Ru 2 O 7 .Single crystals of Ca 1.8 Sr 0.2 RuO 4 were grown by the flux-feeding floating-zone technique [30,31]. ARPES experiments were carried o...

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.