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Semimetallic ${\mathrm{MoTe}}_{2}$ has recently generated enormous attention due to its topological properties, large magnetoresistance, superconductivity, suitability for homojunction phase patterning, and, in particular, metal-insulator transition of thin layers, possibly indicating a quantum spin hall state. These observations prove the potential of ${\mathrm{MoTe}}_{2}$ for thin film applications and call for systematic investigations of the thickness dependent electronic structure. Here we apply angle-resolved photoemission spectroscopy supported by band structure calculations to elucidate the electronic structure of exfoliated $1{\mathrm{T}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{MoTe}}_{2}$. Electron and hole pockets of the inverted conduction and valence bands near $\mathrm{\ensuremath{\Gamma}}$ are resolved down to the monolayer. The Fermi level of exfoliated $1{\mathrm{T}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{MoTe}}_{2}$ monolayers lays within the electron pockets indicating intrinsic $n$-type doping. ${E}_{F}$ shifts downward with increasing thickness consistent with a surface driven mechanism. Our study provides insight on the electronic properties of semimetallic $1{\mathrm{T}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{MoTe}}_{2}$ as an indispensable ingredient for future thin film functionalization.

The long search for materials carrying quantum spin liquid states has recently led to $\ensuremath{\alpha}$-RuCl${}_{3}$, a layered honeycomb Mott insulator with substantial spin-orbit coupling. Often, controlled doping of materials with strong 2D character generates new exotic properties as well as a better understanding of the parent compound. This paper shows that the intercalation compound K${}_{0.5}$RuCl${}_{3}$ sustains a peculiar charge disproportionation into formally Ru${}^{2+}$ and Ru${}^{3+}$. Every Ru${}^{3+}$ with one hole in the t${}_{2g}$ shell is surrounded by Ru${}^{2+}$ where the t${}_{2g}$ level is full and magnetically inert. Thus each type of Ru sites forms a triangular lattice and nearest-neighbor interactions of the original honeycomb are blocked.

Novel ground states might be realized in honeycomb lattices with strong spin-orbit coupling. Here we study the electronic structure of α-RuCl_{3}, in which the Ru ions are in a d^{5} configuration and form a honeycomb lattice, by angle-resolved photoemission, x-ray photoemission, and electron energy loss spectroscopy supported by density functional theory and multiplet calculations. We find that α-RuCl_{3} is a Mott insulator with significant spin-orbit coupling, whose low energy electronic structure is naturally mapped onto J_{eff} states. This makes α-RuCl_{3} a promising candidate for the realization of Kitaev physics. Relevant electronic parameters such as the Hubbard energy U, the crystal field splitting 10 Dq, and the charge transfer energy Δ are evaluated.

We investigated LaAlO${}_{3}$-SrTiO${}_{3}$ heterointerfaces grown either in oxygen-rich or -poor atmosphere by soft x-ray spectroscopy. Resonant photoemission across the Ti L${}_{2,3}$ absorption edge of the valence band and Ti 2$p$ core-level spectroscopy directly monitor the impact of oxygen treatment upon the electronic structure. Two types of Ti${}^{3+}$ related charge carriers are identified. One is located at the Fermi energy and related to the filling of the SrTiO${}_{3}$ conduction band. It appears for low oxygen pressure only. The other one is centered at ${E}_{B}\ensuremath{\approx}1$ eV and independent of the oxygen pressure during growth. It is probably due to defects. The magnitude of both excitations is comparable. It is shown that low oxygen pressure is detrimental for the Ti-O bonding. Our results shed light on the nature of the charge carriers in the vicinity of the LaAlO${}_{3}$-SrTiO${}_{3}$ interface.

We probe the correlation regime of ${\text{Ba}}_{1\ensuremath{-}x}{\text{K}}_{x}{\text{Fe}}_{2}{\text{As}}_{2}$ single crystals by x-ray photoemission spectroscopy. Although the data explicitly confirm the itinerant character of the electrons, the satellite features observed at the ${L}_{3}$ threshold indicate at the same time local behavior. This dichotomy suggests that, although the pnictides appear to be unusually weakly correlated, local electronic excitations cannot be neglected for the correct description of the material.

We have investigated the electronic structure of ${\text{Sr}}_{14\ensuremath{-}x}{\text{Ca}}_{x}{\text{Cu}}_{24}{\text{O}}_{41}$ $(x=0;\text{ }11.5)$ single crystals by angle-resolved photoemission spectroscopy. A satisfactory agreement with band-structure calculations is found. The Fermi surface is observed for ${\text{Sr}}_{2.5}{\text{Ca}}_{11.5}{\text{Cu}}_{24}{\text{O}}_{41}$ from which we derive a charge carrier concentration between 0.15 and 0.2 holes per Cu atom at $T=25\text{ }\text{K}$ in the ladder substructure. The chain substructures, on the other hand, act as diffraction grating for the ladder photoelectrons giving rise to incommensurate replicas of the ladder bands.

We investigate the low energy electronic structure of Ba1-xKxFe2As2 (x=0; 0.3, T_{c}=32 K) single crystals by angle-resolved photoemission spectroscopy with a focus on the renormalization of the dispersion. A kink feature is detected at E approximately 25 meV for the doped compound which vanishes at T=200 K but stays virtually constant when T_{c} is crossed. Our experimental findings rule out the magnetic resonance mode as the origin of the kink and render conventional electron-phonon coupling unlikely. They put stringent restrictions on the dominant source of the electronic interaction channel.

The precise momentum dependence of the superconducting gap in the iron-arsenide superconductor ${\text{Ba}}_{1\ensuremath{-}x}{\text{K}}_{x}{\text{Fe}}_{2}{\text{As}}_{2}$ (BKFA) with ${T}_{c}=32\text{ }\text{K}$ was determined from angle-resolved photoemission spectroscopy (ARPES) via fitting the distribution of the quasiparticle density to a model. The model incorporates finite lifetime and experimental resolution effects, as well as accounts for peculiarities of BKFA electronic structure. We have found that the value of the superconducting gap is practically the same for the inner $\ensuremath{\Gamma}$ barrel, $\mathrm{X}$ pocket, and ``blade'' pocket, and equals 9 meV, while the gap on the outer $\ensuremath{\Gamma}$ barrel is estimated to be less than 4 meV, resulting in $2\ensuremath{\Delta}/{k}_{B}{T}_{c}=6.8$ for the large gap and $2\ensuremath{\Delta}/{k}_{B}{T}_{c}l3$ for the small gap. A large $(77\ifmmode\pm\else\textpm\fi{}3\text{ }%)$ nonsuperconducting component in the photoemission signal is observed below ${T}_{c}$. Details of gap extraction from ARPES data are discussed in Appendixes A,B.

We have investigated the low-energy electronic structure of the heavy-fermion superconductor ${\text{CeCoIn}}_{5}$ by angle-resolved photoemission and band-structure calculations. We measured the Fermi surface and energy distribution maps along the high-symmetry directions at $h\ensuremath{\nu}=100\text{ }\text{eV}$ and $T=25\text{ }\text{K}$. The compound has quasi-two-dimensional Fermi-surface sheets centered at the $M\text{\ensuremath{-}}A$ line of the Brillouin zone. The band-structure calculations have been carried out within the local-density approximation where the $4f$ electrons have been treated either localized or itinerant. We discuss the comparison to the experimental data and the implications for the nature of the $4f$ electrons at the given temperature.

We investigated the recently found superconductor ${\text{LaFeAsO}}_{1\ensuremath{-}x}{\text{F}}_{x}$ by x-ray absorption spectroscopy. From a comparison of the $\text{O}\text{ }K$ edge with LDA calculations we find good agreement and are able to explain the structure and changes in the spectra with electron doping. From experimental $\text{Fe}\text{ }{L}_{2,3}$-edge spectra and charge-transfer multiplet calculations we gain further information on important physical values such as the hopping parameters, the charge-transfer energy $\ensuremath{\Delta}$, and the Hubbard $U$. Furthermore we find the system to be very covalent with a large amount of ligand holes. A shift in the chemical potential is visible in the $\text{O}\text{ }K$- and $\text{Fe}\text{ }{L}_{2,3}$-edge spectra which emphasizes the importance of band effects in these compounds. From the entirety of our results we conclude that LaFeAsO is a bandwidth-dominated material.

We have investigated the electronic structure of LaFeAsO$_{1-x}$F$_{x}$ (x = 0; 0.1; 0.2) by angle-integrated photoemission spectroscopy and local density approximation (LDA) based band structure calculations. The valence band consists of a low energy peak at E = -0.25 eV and a broad structure around E = -5 eV in qualitative agreement with LDA. From the photon energy dependence of these peaks we conclude that the former derives almost exclusively from Fe 3d states. This constitutes experimental evidence for the strong iron character of the relevant states in a broad window around EF and confirms theoretical predictions., Comment: 12 pages, 3 figures

Angle-resolved photoemission spectroscopy (ARPES) provides a detailed view of the renormalized band structure and, consequently, is a key to the self-energy and the single-particle Green's function. Here, we summarize the ARPES data accumulated over the whole Brillouin zone for the optimally doped ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8\ensuremath{-}\ensuremath{\delta}}$ into a parametric model of the Green's function, which we use for calculating the itinerant component of the dynamic spin susceptibility in absolute units with many-body effects taken into account. By comparison with inelastic neutron scattering (INS) data, we show that the itinerant component of the spin response can account for the integral intensity of the experimental INS spectrum. Taking into account the bilayer splitting, we explain the magnetic resonances in the acoustic (odd) and optic (even) INS channels.

Angle-resolved photoemission spectroscopy (ARPES) is used to study the spectral function of the optimally doped high-${T}_{c}$ superconductor $(\mathrm{Bi},\mathrm{Pb}{)}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ in the vicinity of the antinodal point in the superconducting state. Using a parametrized self-energy function, it was possible to describe both the coherent and the incoherent spectral weight of the bonding and the antibonding band. The renormalization effects can be assigned to a very strong coupling to the magnetic resonance mode and at higher energies to a bandwidth renormalization by a factor of two, probably caused by a coupling to a continuum. The present reevaluation of the ARPES data allows one to come to a more reliable determination of the value of the coupling strength of the charge carriers to the mode. The experimental results for the dressing of the charge carriers are compared to theoretical models.

We apply the new-generation angle-resolved photoemission spectroscopy methodology to the most widely studied cuprate superconductor YBa2Cu3O(6+x). Considering the nodal direction, we found noticeable renormalization effects known as kinks both in the quasiparticle dispersion and scattering rate, the bilayer splitting, and evidence for strong interband scattering--all the characteristic features of the nodal quasiparticles detected earlier in Bi2Sr2CaCu2O(8+delta). The typical energy scale and the doping dependence of the kinks clearly point to their intimate relation with the spin-1 resonance seen in the neutron scattering experiments. Our findings strongly suggest a universality of the electron dynamics in the bilayer superconducting cuprates and a dominating role of the spin fluctuations in the formation of the quasiparticles along the nodal direction.

We report the observation of a novel effect in the bilayer $\mathrm{Pb}\mathrm{\text{\ensuremath{-}}}{\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ (Pb-Bi2212) high-${T}_{c}$ superconductor by means of angle-resolved photoemission with circularly polarized excitation. Different scattering rates, determined as a function of energy separately for the bonding and antibonding copper-oxygen bands, strongly imply that the dominating scattering channel is odd with respect to layer exchange within a bilayer. This is inconsistent with a phonon-mediated scattering and favors the participation of the odd collective spin excitations in the scattering mechanism in near-nodal regions of the $\mathbf{k}$ space, suggesting a magnetic nature of the pairing mediator.

Performing an in-depth analysis of the photoemission spectra along the nodal direction of the high-temperature superconductor Bi-2212 we developed a procedure to determine the underlying electronic structure and established a precise relation of the measured quantities to the real and imaginary parts of the self-energy of electronic excitations. The self-consistency of the procedure with respect to the Kramers-Kronig transformation allows us to draw conclusions on the applicability of the spectral function analysis and on the existence of well-defined quasiparticles along the nodal direction even for the underdoped Bi-2212 in the pseudogap state. The analysis of the real part of the self-energy ${\ensuremath{\Sigma}}^{\ensuremath{'}}(\ensuremath{\omega})$ for an overdoped and underdoped Bi-2212 helps to distinguish the $70\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ ``kink'' from ${\ensuremath{\Sigma}}^{\ensuremath{'}}(\ensuremath{\omega})$ maximum and conclude about doping dependence of the kink strength.

We use angle-resolved photoemission with circularly polarized excitation to demonstrate that in the 5x1 superstructure-free Pb-Bi2212 material there are no signatures of time-reversal symmetry breaking in the sense of the criteria developed earlier (Kaminski et al. Nature {\bf 416}, 610 (2002)). In addition to the existing technique, we suggest and apply an independent experimental approach to prove the absence of the effect in the studied compounds. The dichroic signal retains reflection antisymmetry as a function of temperature and doping and in all mirror planes, precisely defined by the experimental dispersion at low energies. The obtained results demonstrate that the signatures of time-reversal symmetry violation in pristine Bi2212, as determined by ARPES, are not a universal feature of all cuprate superconductors., 4.5 RevTEX pages, 4 figures, after referees

Angle-resolved photoemission spectroscopy (ARPES) is used to study the doping dependence of the lifetime and the mass renormalization of the low-energy excitations in high-${T}_{c}$ cuprate $(\mathrm{B}\mathrm{i},\mathrm{P}\mathrm{b}{)}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ along the zone diagonal. We find a linear energy dependence of the scattering rate for the underdoped samples and a quadratic energy dependence for the overdoped case. The mass enhancement of the quasiparticles due to the many body effects at the Fermi energy is found to be in the order of 2 and the renormalization extends over a large energy range for both the normal and the superconducting state. The much discussed kink in the dispersion around 70 meV is interpreted as a small additional effect at low temperatures.

Angle-resolved photoemission spectroscopy is used to study the mass renormalization of the charge carriers in the high-${T}_{c}$ superconductor $(\mathrm{P}\mathrm{b},\mathrm{B}\mathrm{i}{)}_{2}{\mathrm{S}\mathrm{r}}_{2}{\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{u}}_{2}{\mathrm{O}}_{8}$ in the vicinity of the $(\ensuremath{\pi},0)$ point in the superconducting and the normal states. Using matrix element effects at different photon energies and due to a high momentum and energy resolution the bonding and the antibonding bands could be separated in the whole dopant range. A huge coupling to a bosonic collective mode is observed below ${T}_{c}$ for both bands, in particular, for the underdoped case. Above ${T}_{c}$, a weaker coupling to a continuous spectrum of modes is detected.

High-resolution angle-resolved photoemission with variable excitation energies is used to disentangle bilayer splitting effects and intrinsic (self-energy) effects in the electronic spectral function near the ($\ensuremath{\pi},0$) point of differently doped $(\mathrm{P}\mathrm{b},\mathrm{B}\mathrm{i}{)}_{2}{\mathrm{S}\mathrm{r}}_{2}{\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{u}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$. In contrast to overdoped samples, where intrinsic effects at the ($\ensuremath{\pi},0$) point are virtually absent, we find in underdoped samples intrinsic effects in the superconducting-state ($\ensuremath{\pi},0$) spectra of the antibonding band. This intrinsic effect is present only below the critical temperature and weakens considerably with doping. Our results give strong support for models which involve a strong coupling of electronic excitations with the resonance mode seen in inelastic neutron scattering experiments.

We have studied the core level photoemission spectra of the two-dimensional cuprates Sr 2 CuO 2 Cl 2 , Sr 2 CuO 2 Br 2 . Ca 2 CuO 2 Cl 2 . Bi 2 Sr 2 CaCu 2 O 8 + Φ , and Nd 2 CuO 4 , with particular focus on the screening response to core-hole creation in the Cu-2p 3 / 2 level. The influence of the apex positions on the shape of the so-called main line is investigated, and found to be weak. Additionally, an Anderson impurity model was used to fit the shape of the main lines, obtaining good agreement with the data from Nd 2 CuO 4 . For the other compounds, while the energy spread of the two screening channels (local and nonlocal) is well reproduced, the theory underestimates the width of the nonlocally screened feature. The shapes of the main lines are discussed in detail.