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The interface of manganese(II) phtalocyanine (MnPc) with an α-RuCl3 single crystal is studied by means of photoelectron spectroscopy. The organic molecule was evaporated on top of an in situ cleaved α-RuCl3 bulk crystal in steps. The work function and electron affinity of α-RuCl3 is determined to be 6.3 and 5.4 eV, respectively, in line with common fluorinated acceptor molecules, but with the potential to absorb more electrons per area at interfaces with other materials. These favorable electronic properties lead to a charge transfer from MnPc to α-RuCl3 which manifests itself mainly in peak shape changes of core level photoemission spectra and further filling of Ru 4d states as revealed by valence band photoemission. This work demonstrates the promising potential of α-RuCl3 as a strong acceptor material for interfaces in general, and for organic molecules in particular.

Their exceptional optical properties are a driving force for the persistent interest in atomically thin transition metal dichalcogenides such as MoS2. The optical response is dominated by excitons. Apart from the bright excitons, which directly couple to light, it has been realized that dark excitons, where photon absorption or emission is inhibited by the spin state or momentum mismatch, are decisive for many optical properties. However, in particular the momentum dependence is difficult to assess experimentally and often remains elusive or is investigated by indirect means. Here we study the momentum dependent electronic structure experimentally and theoretically. We use angle-resolved photoemission as a one-particle probe of the occupied valence band structure and electron energy loss spectroscopy as a two-particle probe of electronic transitions across the gap to benchmark a single-particle model of the dielectric function $$\epsilon ({\bf{q}},\omega )$$ ϵ(q,ω) against momentum dependent experimental measurements. This ansatz captures key aspects of the data surprisingly well. In particular, the energy region where substantial nesting occurs, which is at the origin of the strong light–matter interaction of thin transition metal dichalcogenides and crucial for the prominent C-exciton, is described well and spans a more complex exciton landscape than previously anticipated. Its local maxima in $$({\bf{q}}\ \ne \ 0,\omega )$$ (q≠0,ω) space can be considered as dark excitons and might be relevant for higher order optical processes. Our study may lead to a more complete understanding of the optical properties of atomically thin transition metal dichalcogenides.

Investigation of the influence of the nanocrystal (NC) surface chemistry on the (opto)electronic properties of NC-based thin films is of paramount importance for their further application in variou...

In this work, we present a new synthetic approach to colloidal PbS nanoplatelets (NPLs) utilizing a cation exchange (CE) strategy starting from CuS NPLs synthesized via the hot-injection method. Whereas the thickness of the resulting CuS NPLs was fixed at approx. 5 nm, the lateral size could be tuned by varying the reaction conditions, such as time from 6 to 16 h, the reaction temperature (120 °C, 140 °C), and the amount of copper precursor. In a second step, Cu+ cations were replaced with Pb2+ ions within the crystal lattice via CE. While the shape and the size of parental CuS platelets were preserved, the crystal structure was rearranged from hexagonal covellite to PbS galena, accompanied by the fragmentation of the monocrystalline phase into polycrystalline one. Afterwards a halide mediated ligand exchange (LE) was carried out in order to remove insulating oleic acid residues from the PbS NPL surface and to form stable dispersions in polar organic solvents enabling thin-film fabrication. Both CE and LE processes were monitored by several characterization techniques. Furthermore, we measured the electrical conductivity of the resulting PbS NPL-based films before and after LE and compared the processing in ambient to inert atmosphere. Finally, we fabricated field-effect transistors with an on/off ratio of up to 60 and linear charge carrier mobility for holes of 0.02 cm2 V−1 s−1.

Conducting domain walls (CDWs) in ferroelectric materials are promising candidates for applications in a manifold of nanoscale, optoelectronic devices. Characterization of their microscopic properties, however, remains challenging due to their small dimension and highly insulating environment. Here, we inspect individual CDWs in single-crystalline LiNbO3 by the combination of photoemission electron microscopy (PEEM) and second harmonic generation (SHG) microscopy. While SHG unveils the overall domain wall inclination angle α, PEEM is sensitive to local conductance variations, both at and away from the domain wall. Thus, the two imaging techniques deliver complementary information over a large field of view. In agreement with earlier theoretical predictions we find that the local conductance is dictated by α and reveal a quantitative connection between them. Our results help to elucidate the electronic structure of CDWs and underline the value of PEEM as a non-contact characterization tool for mapping local conductance variations in highly resistive environments.

Quasi-two-dimensional (2D) CdSe nanoplatelets (NPLs) are distinguished by their unique optical properties in comparison to classical semiconductor nanocrystals, such as extremely narrow emission line widths, reduced Auger recombination, and relatively high absorption cross sections. Inherent to their anisotropic 2D structure, however, is the loss of continuous tunability of their photoluminescence (PL) properties due to stepwise growth. On top of that, limited experimental availability of NPLs of different thicknesses and ultimately the bulk band gap of CdSe constrain the achievable PL wavelengths. Here, we report on the doping of CdSe NPLs with mercury, which gives rise to additional PL in the red region of the visible spectrum and in the near-infrared region. We employ a seeded-growth method with injection solutions containing cadmium, selenium, and mercury. The resulting NPLs retain their anisotropic structure, are uniform in size and shape, and present significantly altered spectroscopic characteristics due to the existence of additional energetic states. We conclude that doping takes place by employing elemental analysis in combination with PL excitation spectroscopy, X-ray photoelectron spectroscopy, and single-particle fluorescence spectroscopy, confirming single emitters being responsible for multiple distinct emission signals.

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.

Kitaev-type interactions between neighbouring magnetic moments emerge in the honeycomb material ${\alpha}$-RuCl3. It is debated however whether these Kitaev interactions are ferromagnetic or antiferromagnetic. With electron energy loss spectroscopy (EELS) we study the lowest excitation across the Mott-Hubbard gap, which involves a d4 triplet in the final state and therefore is sensitive to nearest-neighbor spin-spin correlations. At low temperature the spectral weight of these triplets is strongly enhanced, in accordance with optical data. We show that the magnetic correlation function that determines this EELS spectral weight is directly related to a Kitaev-type spin-spin correlator and that the temperature dependence agrees very well with the results of a microscopic magnetic Hamiltonian for ${\alpha}$-RuCl3 with ferromagnetic Kitaev coupling., Comment: 5 pages, 3 figures

Focused ion irradiation of insulating diamond-like carbon (DLC) films is a well-recognized approach to write defined nanostructures with drastically changed properties compared to the unexposed matrix. In particular, the electrical conductivity of the film areas that are irradiated increases by several orders of magnitude. Furthermore it is known that the conductivity increase is directly related to the irradiation-induced sp3–sp2 rehybridization. This experimental work shows in detail that ion-induced microstructural ordering of the carbon atom arrangement far beyond the sp3–sp2 conversion saturation is an important microscopic mechanism for the alteration of physical properties, including an increase in the conductivity. The atomic ordering correlates with the local energy density deposited during the ion impact. Thus the ion-induced phase transformation of DLC is proposed to comprise a rehybridization stage, caused by nuclear collisions, and a rearrangement stage (graphite-like ordering) that is thermally driven by the ion impact. These conclusions are based on in-depth investigations of amorphous DLC films that were locally irradiated by a number of ion species employing several temperature regimes. The ion irradiation experiments cover a wide range of fluences. X-ray photoelectron spectroscopy, μ-Raman spectroscopy, transmission electron microscopy, and low temperature transport measurements have been applied to characterize the films.

Combining dissimilar transition metal oxides (TMOs) into artificial heterostructures enables to create electronic interface systems with new electronic properties that do not exist in bulk. A detailed understanding of how such interfaces can be used to tailor physical properties requires characterization techniques capable to yield interface sensitive spectroscopic information with monolayer resolution. In this regard resonant x-ray reflectivity (RXR) provides a unique experimental tool to achieve exactly this. It yields the element specific electronic depth profiles in a non-destructive manner. Here, using a YBa2Cu3O7−δ (YBCO) thin film, we demonstrate that RXR is further capable to deliver site selectivity. By applying a new analysis scheme to RXR, which takes the atomic structure of the material into account, together with information of the local charge anisotropy of the resonant ions, we obtained spectroscopic information from the different Cu sites (e.g., chain and plane) throughout the film profile. While most of the film behaves bulk-like, we observe that the Cu-chains at the surface show characteristics of electron doping, whereas the Cu-planes closest to the surface exhibit an orbital reconstruction similar to that observed at La1−x Ca x MnO3/YBCO interfaces.

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.

Here we apply high resolution angle-resolved photoemission spectroscopy (ARPES) using a wide excitation energy range to probe the electronic structure and the Fermi surface topology of the Ba 1− x K x Fe 2 As 2 ( T c = 32 K) superconductor. We find significant deviations in the low energy band structure from that predicted in calculations. A set of Fermi surface sheets with unexpected topology is detected at the Brillouin zone boundary. At the X -symmetry point the Fermi surface is formed by a shallow electron-like pocket surrounded by four hole-like pockets elongated in Γ − X and Γ − Y directions.

LaAlO$_{3}$ and NdGaO$_{3}$ thin films of different thickness have been grown by pulsed laser deposition on TiO$_2$-terminated SrTiO$_{3}$ single crystals and investigated by soft X-ray photoemission spectroscopy. The surface sensitivity of the measurements has been tuned by varying photon energy $h\nu$ and emission angle $\Theta$. In contrast to the core levels of the other elements, the Sr $3d$ line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From our quantitative analysis we conclude that during the growth process Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide.

While the pronounced doping dependence of the quasiparticle spectral weight in the antinodal region of the superconducting cuprates, as seen by ARPES, unambiguously points to the magnetic origin of the strong electron-boson coupling there, the nature of the electron scattering in the nodal direction remained unclear. Here we present a short review of our recent detailed investigations of the nodal direction of Bi-2212. Our findings prove the existence of well defined quasiparticles even in the pseudogap state and show that the essential part of the quasiparticle scattering rate, which appears on top of Auger-like electron-electron interaction, also implies a magnetic origin., 6 revtex pages, short review, presented at SNS 2004

We have investigated the properties of cleaved ${\mathrm{SmB}}_{6}$ single crystals by x-ray photoelectron spectroscopy. At low temperatures and freshly cleaved samples a surface core level shift is observed which vanishes when the temperature is increased. A Sm valence between 2.5 and 2.6 is derived from the relative intensities of the ${\mathrm{Sm}}^{2+}$ and ${\mathrm{Sm}}^{3+}$ multiplets. The B/Sm intensity ratio obtained from the core levels is always larger than the stoichiometric value. Possible reasons for this deviation are discussed. The B 1s signal shows an unexpected complexity: An anomalous low energy component appears with increasing temperature and is assigned to the formation of a suboxide at the surface. While several interesting intrinsic and extrinsic properties of the ${\mathrm{SmB}}_{6}$ surface are elucidated in this manuscript, no clear indication of a trivial mechanism for the prominent surface conductivity is found.

The electronic properties of NdGaO3/SrTiO3, LaGaO3/SrTiO3 and LaAlO3/SrTiO3 interfaces, all showing an insulator-to-metal transition as a function of the overlayer-thickness, are addressed in a comparative study based on x-ray absorption, x-ray photoemission and resonant photoemission spectroscopy. The nature of the charge carriers, their concentration and spatial distribution as well as the interface band alignments and the overall interface band diagrams are studied and quantitatively evaluated. The behavior of the three analyzed heterostructures is found to be remarkably similar. The valence band edge of all the three overlayers aligns to that of bulk SrTiO3. The near-interface SrTiO3 layer is affected, at increasing overlayer thickness, by the building-up of a confining potential. This potential bends both the valence and the conduction band downwards. The latter one crossing the Fermi energy in the proximity of the interface and determines the formation of an interfacial band offset growing as a function of thickness. Quite remarkably, but in agreement with previous reports for LaAlO3/SrTiO3, no electric field is detected inside any of the polar overlayers. The essential phenomenology emerging from our findings is discussed on the base of different alternative scenarios regarding the origin of interface carriers and their interaction with an intense photon beam.

We report studies of the electronic structure and elementary excitations of doped and undoped cuprate chains, ladders and planes. Using high energy spectroscopies such as x-ray absorption, core level photoemission and angle resolved photoemission spectroscopy, important information regarding the charge distribution and hole dynamics can be obtained. The comparison of the experimental data with suitable theoretical models sets constraints on the parameters entering into the model calculations, and offers insight into the important physical quantities governing the electronic structure of these materials. Recurring themes include the importance of the dimensionality of the Cu-O network (1D->2D) and the crucial role played by the spin-background in determining the dynamics of low-lying excitations in these strongly correlated systems., J. Electron Spec. Relat. Phenom.: special issue on electron correlation, in press

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

Some heavy fermion materials show so-called hidden-order phases which are invisible to many characterization techniques and whose microscopic origin remained controversial for decades. Among such hidden-order compounds, CeB6 is of model character due to its simple electronic configuration and crystal structure. Apart from more conventional antiferromagnetism, it shows an elusive phase at low temperatures, which is commonly associated with multipolar order. Here we show that this phase roots in a Fermi surface instability. This conclusion is based on a full 3D tomographic sampling of the electronic structure by angle-resolved photoemission and comparison with inelastic neutron scattering data. The hidden order is mediated by itinerant electrons. Our measurements will serve as a paradigm for the investigation of hidden-order phases in f-electron systems, but also generally for situations where the itinerant electrons drive orbital or spin order., In compounds containing 4f and 5f elements, hidden-order phases exist which are undetectable by many methods, the origins of which are debated. Here, the authors use photoemission and neutron scattering methods to show how such a multipolar-ordered phase emerges due to Fermi surface instability in CeB6.

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.

In this contribution we first present a short introduction into the lattice structure, the phase diagram and the electronic structure of high-Tc superconduc- tors. Then we explain the principles of angle-resolved photoemission spectroscopy (ARPES) and the influence of the dressing of the charge carriers, which is normally described by the complex self-energy function, on the spectral function in the nor- mal and the superconducting state. Finally we review our recent ARPES results on high-Tc superconductors at various k-points in the Brillouin zone near the Fermi surface. Information on the dressing of the charge carriers, i.e., on the effective mass and the scattering length, is obtained as a function of doping concentration, tem- perature, momentum and energy. The strong renormalization of the bandstructure due to the dressing can be explained in terms of a coupling to a continuum of spin fluctuations and in the superconducting state by an additional coupling to a triplet exciton excitation. Possibly, this dressing is related to the glue for the pair formation in cuprate superconductors.

We show that in the angle resolved photoemission spectroscopy (ARPES) near-surface induced fields can be useful for disentangling the surface and bulk related emission. The jump of the dielectric function at the interface results in a nonzero term $\operatorname{div}\textbf{A}$ in the photoemission matrix element. The term happens to be significant approximately within the first unit cell and leads to the circular dichroism for the states localized therein. As an example we use ARPES spectra of an YBa$_2$Cu$_3$O$_{7-\delta}$ crystal to distinguish between the overdoped surface related component and its bulk counterparts., Comment: 4 pages, 2 figures

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.

Angle resolved photoemission spectroscopy (ARPES) provides a detailed view of the renormalized band structure in cuprates and, consequently, is a key to the self-energy and the quasiparticle Green's function. Such information gives a clue to the comparison of ARPES with scanning tunneling microscopy, inelastic neutron scattering (INS), and Raman scattering data. Here we touch on a potential possibility of such a comparison with the dynamical magnetic susceptibility measured in INS experiments. Calculations based on the experimentally measured quasiparticle self-energies in cuprates lead to the estimated magnetic susceptibility response with many-body effects taken into account., Will be presented at the M2S-HTSC-VIII conference in Dresden

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.

One of the mysteries of modern condensed-matter physics is the nature of the pseudogap state of the superconducting cuprates. Kaminski et al. claim to have observed signatures of time-reversal symmetry breaking in the pseudogap regime in underdoped Bi2Sr2CaCu2O8+delta (Bi2212). Here we argue that the observed circular dichroism is due to the 51 superstructure replica of the electronic bands and therefore cannot be considered as evidence for spontaneous time-reversal symmetry breaking in cuprates.

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.

One of the most remarkable properties of the high-temperature superconductors is a pseudogap regime appearing in the underdoped cuprates above the superconducting transition temperature T_c. The pseudogap continously develops out of the superconducting gap. In this paper, we demonstrate by means of a detailed comparison between theory and experiment that the characteristic change of quasiparticle dispersion in crossing T_c in the underdoped cuprates can be understood as being due to phase fluctuations of the superconducting order parameter. In particular, we show that within a phase fluctuation model the characteristic back-turning BCS bands disappear above T_c whereas the gap remains open. Furthermore, the pseudogap rather has a U-shape instead of the characteristic V-shape of a d_{x^2-y^2}-wave pairing symmetry and starts closing from the nodal k=(pi/2,pi/2) directions, whereas it rather fills in at the anti-nodal k=(pi,0) regions, yielding further support to the phase fluctuation scenario., 6 pages, 4 eps-figures

We used angle-resolved photoemission spectroscopy to study the shadow Fermi surface in one layer Bi2Sr1.6La0.4CuO6+delta and two layer (Bi,Pb)2Sr2CaCu2O8+delta. We find the shadow band to have the same peakwidth and dispersion as the main band. In addition, the shadow band/main band intensity ratio is found to be binding energy independent. Consequently, it is concluded that the shadow bands in Bi-based HTSC do not originate from antiferromagnetic interactions but have a structural origin., 10 pages, 2 figures

Studying the nodal quasiparticles in superconducting cuprates by photoemission with highly improved momentum resolution, we show that a new "kink" feature in the scattering rate is a key to uncover the nature of electron correlations in these compounds. Our data provide evidence that the main doping independent contribution to the scattering can be well understood in terms of the conventional Fermi liquid model, while the additional doping dependent contribution has a magnetic origin. This sheds doubt on applicability of a phonon-mediated pairing mechanism to high temperature superconductors., Comment: rextex, 4 pages, 4 figures

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.

We investigated CeTIn5 (T = Co, Rh, Ir) using temperature- and angle-dependent x-ray photoemission spectroscopy. The Ce 3d core level has a very similar shape for all three materials and is indicative of weak f-hybridization. The spectra were analyzed using a simplified version of the Anderson impurity model, which yields a Ce 4f occupancy that is larger than 0.9. The temperature dependence shows a continuous, irreversible and exclusive broadening of the Ce 3d peaks, due to oxidation of Ce at the surface.