We investigate the normal state of the ''11'' iron-based superconductor FeSe 0:42 Te 0:58 by angle-resolved photoemission. Our data reveal a highly renormalized quasiparticle dispersion characteristic of a strongly correlated metal. We find sheet dependent effective carrier masses between %3 and 16m e corresponding to a mass enhancement over band structure values of m à =m band % 6-20. This is nearly an order of magnitude higher than the renormalization reported previously for iron-arsenide superconductors of the ''1111'' and ''122'' families but fully consistent with the bulk specific heat.

We explore the interplay of electron-electron correlations and spin-orbit coupling in the model Fermi liquid Sr2RuO4 using laser-based angle-resolved photoemission spectroscopy. Our precise measurement of the Fermi surface confirms the importance of spin-orbit coupling in this material and reveals that its effective value is enhanced by a factor of about two, due to electronic correlations. The self-energies for the β and γ sheets are found to display significant angular dependence. By taking into account the multi-orbital composition of quasiparticle states, we determine self-energies associated with each orbital component directly from the experimental data. This analysis demonstrates that the perceived angular dependence does not imply momentum-dependent many-body effects, but arises from a substantial orbital mixing induced by spin-orbit coupling. A comparison to single-site dynamical mean-field theory further supports the notion of dominantly local orbital self-energies, and provides strong evidence for an electronic origin of the observed non-linear frequency dependence of the self-energies, leading to 'kinks' in the quasiparticle dispersion of Sr2RuO4. * present address: ISIS Facility, Rutherford

We present a quantum-kinetic theory of the excitation transfer in a quantum dot molecule. We derive the consistent Markovian limit for the system kinetics, which leads to a description in terms of a single transfer rate for weak coupling. We show that the transfer rate is a strongly varying, nonmonotonic function of the spatial separation and energy mismatch between the dots.

We present angle-resolved photoemission data from Cu(111). Using a focused 6 eV continuous-wave laser for photoexcitation, we achieve a high effective momentum resolution, enabling detection of the Rashba spin splitting in the Shockley surface state on Cu(111). The magnitude of the spin splitting of k ∼ 0.006Å −1 is surprisingly large and exceeds values predicted for the analogous surface state on Ag(111), but is reproduced by first-principles calculations. We further resolve a kink in the dispersion, which we attribute to electron-phonon coupling.

We investigate the bilayer Ruddlesden-Popper iridate Sr 3 Ir 2 O 7 by temperature-dependent angle-resolved photoemission. At low temperatures, we find a fully gapped correlated insulator, characterized by a small charge gap and narrow bandwidths. The low-energy spectral features show a pronounced temperature-dependent broadening and non-quasiparticle-like Gaussian line shapes. Together, these spectral features provide experimental evidence for a polaronic ground state. We observe similar behavior for the single-layer cousin Sr 2 IrO 4 , indicating that strong electron-boson coupling dominates the low-energy excitations of this exotic family of 5d compounds. The strong spin-orbit interaction in the 5d shell is predicted to stabilize a variety of exotic ground states in iridium-based transition-metal oxides, including Mott insulators, 1-3 Weyl semimetals, 4 correlated topological insulators, 5-8 and spintriplet superconductors.9 Moreover, iridates were recently proposed as an analog of the cuprates, and as such, a potential platform for engineering high-temperature superconductivity. 10This initially appears surprising given the weak influence of electron correlations expected for spatially extended 5d orbitals. Nonetheless, Sr 2 IrO 4 and Sr 3 Ir 2 O 7 , which both host partially filled 5d shells, are found to be insulating.11,12 For Sr 2 IrO 4 , this was recently attributed 1,2 to a reconstruction of the underlying electronic structure by a cooperative interplay of structural distortions and, crucially, the strong spin-orbit coupling, leaving a half-filled J eff = 1/2 band that is sufficiently narrow that even moderate correlation strengths can drive a Mott transition. This J eff = 1/2 space can be mapped onto a pseudospin-1/2 Hubbard model, providing the analogy to the cuprates. 10 Microscopically, however, the similarity of the insulating ground states in these parent compounds remains an open question. The orbital configuration is 5d 5 in Sr n+1 Ir n O 3n+1 as compared to 3d 9 in the cuprates. Spin-orbit interactions play an important role in the former, 1,2,13-20 while the behavior of the latter is dominated by strong electron correlations. Even the range of validity of the strong spin-orbit J eff = 1/2 Mott picture for the iridates, on which links to the cuprates have been based, remains an open question. [21][22][23][24][25] As such, detailed studies of the low-energy electronic excitations of iridates are required to elucidate the nature of the complex many-body ground states of these compounds.Indeed, kinetic, Coulomb, crystal-field, and spin-orbit energy scales are all of similar magnitude in the iridates, potentially leading to the close proximity of several competing ground states. For example, optical conductivity measurements revealed a metal-insulator transition (MIT) upon increasing dimensionality through the layered Ruddlesden-Popper series Sr n+1 Ir n O 3n+1 , 3 with the conducting three-dimensional end member predicted to be an exotic semimetal. 26 The n = 2 compound, which crystallizes in an o...

We observe apparent hole pockets in the Fermi surfaces of single-layer Bi-based cuprate superconductors from angle-resolved photoemission. From detailed low-energy electron diffraction measurements and an analysis of the angle-resolved photoemission polarization dependence, we show that these pockets are not intrinsic but arise from multiple overlapping superstructure replicas of the main and shadow bands. We further demonstrate that the hole pockets reported recently from angle-resolved photoemission [Meng et al., Nature (London) 462, 335 (2009)] have a similar structural origin and are inconsistent with an intrinsic hole pocket associated with the electronic structure of a doped CuO₂ plane.

We compare the relativistic LDA Fermi surface of Sr2RuO4 to direct experimental evidence of spin-orbit coupling from de Haas-van Alphen experiments. The k-dependence of the Zeeman splitting at the Fermi surface is modelled with a range of tight binding models of the quasi-particle bands. Only a very restricted class of parameters are consistent with evidence from the de Haas-van Alphen experiments for a strong k-dependent Zeeman splitting on the alpha Fermi surface sheet. The bare LDA bands do not lead to such a strong k-dependent Zeeman splitting on this sheet, and this suggests that additional charge transfer takes place as suggested by DMFT calculations. We conclude that the overall scale of the spin-orbit coupling must be at least as large as the several hundred kelvin deduced in previous work, and that this must call into question any theory postulating rotation of the triplet d-vector at small magnetic fields.

We report angle-resolved photoelectron spectroscopy measurements of the quantum critical metal Sr3Ru2O7 revealing itinerant Ru 4d-states confined over large parts of the Brillouin zone to an energy range of < ∼ 6 meV, nearly three orders of magnitude lower than the bare band width. We show that this energy scale agrees quantitatively with a characteristic thermodynamic energy scale associated with quantum criticality and illustrate how it arises from the hybridization of light and strongly renormalized, heavy quasiparticle bands. For the largest Fermi surface sheet we find a marked k-dependence of the renormalization and show that it correlates with the Ru 4d -O 2p hybridization.