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Hybridization of Bogoliubov quasiparticles (BQPs) between the CuO_{2} layers in the triple-layer cuprate high-temperature superconductor Bi_{2}Sr_{2}Cu_{2}Cu_{3}O_{10+δ} is studied by angle-resolved photoemission spectroscopy (ARPES). In the superconducting state, an anticrossing gap opens between the outer- and inner-BQP bands, which we attribute primarily to interlayer single-particle hopping with possible contributions from interlayer Cooper pairing. We find that the d-wave superconducting gap of both BQP bands smoothly develops with momentum without an abrupt jump in contrast to a previous ARPES study. Hybridization between the BQPs also gradually increases in going from the off nodal to the antinodal region, which is explained by the momentum dependence of the interlayer single-particle hopping. As possible mechanisms for the enhancement of the superconducting transition temperature, the hybridization between the BQPs as well as the combination of phonon modes of the triple CuO_{2} layers and spin fluctuations represented by a four-well model are discussed.

We have carried out hard x-ray photoemission spectroscopy (HAXPES) of Yb

We use a surface-selective angle-resolved photoemission spectroscopy and unveil the electronic nature on the topmost layer of Sr_{2}RuO_{4} crystal, consisting of slightly rotated RuO_{6} octahedrons. The γ band derived from the 4d_{xy} orbital is found to be about three times narrower than that for the bulk. This strongly contrasts with a subtle variation seen in the α and β bands derived from the one-dimensional 4d_{xz/yz}. This anomaly is reproduced by the dynamical mean-field theory calculations, introducing not only the on-site Hubbard interaction but also the significant Hund's coupling. We detect a coherence-to-incoherence crossover theoretically predicted for Hund's metals, which has been recognized only recently. The crossover temperature in the surface is about half that of the bulk, indicating that the naturally generated monolayer of reconstructed Sr_{2}RuO_{4} is extremely correlated and well isolated from the underlying crystal.

We investigate the k z dispersion in the hole Fermi surfaces (FSs) and the superconducting (SC) gaps of BaFe2(As0.65P0.35)2 by employing bulk-sensitive angle-resolved photoemission spectroscopy (ARPES) with low energy photons. We find that this material exhibits a comparable magnitude of SC gaps for three-hole FSs at k z ∼ π . The comparable magnitude of the SC gap is observed also at k z ∼ 0. Since each FS sheet has a distinct orbital character, these observations are an indication of the orbital-independent SC gaps in the hole FSs.

The edge properties of single layer graphene epitaxially grown on partially graphitized 4H-SiC(0001) surface have been investigated with scanning tunneling microscopy (STM). We directly observed the atomic-structure dependency of the super structures in the vicinity of armchair and zigzag edges due to the different kinds of symmetry-breaking at those two edges.

We have performed an angle-resolved photoemission study of the nodal quasi-particle spectra of the high-Tc cuprate tri-layer Bi2Sr2Ca2Cu3O10+d (Tc~ 110 K). The spectral weight Z of the nodal quasi-particle increases with decreasing temperature across the Tc. Such a temperature dependence is qualitatively similar to that of the coherence peak intensity in the anti nodal region of various high-Tc cuprates although the nodal spectral weight remains finite and large above Tc. We attribute this observation to the reduction of electron correlation strength in going from the normal metallic state to the superconducting state, a characteristic behavior of a superconductor with strong electron correlation., 13 pages, 5 figures

In the hole-doped cuprates, a small amount of carriers suppresses antiferromagnetism and induces superconductivity. In the electron-doped cuprates, on the other hand, superconductivity appears only in a narrow range of high electron concentration ($\sim$ doped Ce content) after reduction annealing, and strong antiferromagnetic (AFM) correlation persists in the superconducting phase. Recently, Pr$_{1.3-x}$La$_{0.7}$Ce$_{x}$CuO$_{4}$ (PLCCO) bulk single crystals annealed by a "protect annealing" method showed a high $T_c$ of $\sim$ 27 K for small Ce content down to $x \sim 0.05$. By angle-resolved photoemission spectroscopy (ARPES) measurements of PLCCO crystals, we observed a sharp quasi-particle peak on the entire Fermi surface without signature of an AFM pseudogap unlike all the previous work, indicating a dramatic reduction of AFM correlation length and/or of magnetic moments. The superconducting state was found to extend over a wide electron concentration range. The present ARPES results fundamentally change the long-standing picture on the electronic structure in the electron-doped regime., 23 pages, 7 figures

We study the bulk electronic structure of Na x CoO 2 .yH 2 O using Hard X-ray (HX, h ν = 5.95 KeV) synchrotron photoelectron spectroscopy (PES). The Co 2 p core level spectra show well-separated Co 3 + and Co 4 + ions. Cluster calculations suggest low spin Co 3 + and Co 4 + character, and a moderate on-site Coulomb correlation energy U dd ∼ 3–5.5 eV. Photon-dependent valence band PES identifies Co 3 d and O 2 p derived states, in near agreement with band structure calculations. We discuss the importance of HX-PES for studying correlated transition metal oxides.

We have realized hard X-ray (HX) photoelectron spectroscopy (PES) with high-throughput and high-energy-resolution for core level and valence band studies using high-energy and high-brilliance synchrotron radiation at BL29XU in SPring-8. Large escape depth of high-energy photoelectrons enables us to probe intrinsic bulk states almost free from surface condition. By use of a newly developed electron energy analyzer and well-focused X-rays, high-energy resolution of 75 meV ( E / Δ E = 79 , 000 ) was realized for 5.95 keV photoelectrons.

We study the Mott-Hubbard metal-insulator transition in single-crystal V2O3 using hard X-ray (HX: hν = 5940 eV) core-level photoemission spectroscopy (PES). HX-PES enables a bulk probe of the electronic structure in the paramagnetic metallic and antiferromagnetic insulating phases. Metallic V2O3 shows additional features at low binding energy to the main peak of V 1s, 2p, and 3s core levels, which vanish in the insulating phase. The low-binding-energy features in the metallic phase are also observed using soft X-rays (SX: hν = 1450 eV), but with a reduced relative intensity compared to the HX-PES spectrum. A model cluster calculation including core hole screening by coherent states at the Fermi level, reproduces the low-binding-energy features in the metallic phase. The O 1s core level also shows spectral changes: the asymmetric line shape in the metallic phase transforms to a symmetric line shape in the insulating phase, consistent with the metal-insulator transition. The results indicate screening by coherent states is more effective in the bulk compared to the surface. HX-PES is, thus, a reliable probe of the electronic-structure changes across the metal-insulator transition in strongly correlated electron systems.

We have obtained the Cr 3d-like energy states, which located in the band gap of GaN by means of resonant photoemission spectroscopy. In the difference spectrum between the valence band photoemission spectra of non-doped GaN and that of the Ga0.937Cr0.063N, we observed the new energy state, in band gap, consists of Cr 3d-like and N 2p-like component by strong hybridization.

We show that finite temperature variational cluster approximation (VCA) calculations on an extended Falicov-Kimball model can reproduce angle-resolved photoemission spectroscopy (ARPES) results on ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ across a semiconductor-to-semiconductor structural phase transition at 325 K. We demonstrate that the characteristic temperature dependence of the flat-top valence band observed by ARPES is reproduced by the VCA calculation on the realistic model for an excitonic insulator only when the strong excitonic fluctuation is taken into account. The present calculations indicate that ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ falls in the Bose-Einstein condensation regime of the excitonic insulator state.

We have performed angle-resolved photoemission spectroscopy study of the electronic structure of the tri-layer high- T c cuprate superconductor Bi 2 Sr 2 Ca 2 Cu 3 O 10 + δ and observed separate band dispersions and Fermi surfaces corresponding to the outer and inner CuO2 planes. From the band dispersions, the c-axis hopping parameter t ⊥ between the outer and inner CuO2 planes is estimated to be ∼56 meV.

Valence-band and conduction-band electronic structure of glassy (g-) AsxSe1−x with x=0, 0.16, 0.34, 0.40, 0.44 and 0.55 has been investigated by means of in situ measurements of photoemission and inverse-photoemission spectra. The spectra exhibit changes at x=0.4 in the energy position of Se 4p lone-pair states, the band gap energy and the widths of valence bands and the main peak in the inverse-photoemission spectra. Two peak structures derived from Se-chains also disappear at x=0.4. These changes support the percolation phenomenon predicted for g-AsxSe1−x.

We have measured the photoemission, total yield and partial yield spectra of CeOs 2 in the energy region of the Ce3 d –4 f excitation. In the Ce3 d –4 f resonant photoemission and yield spectra, we observe the following features. (1) In the Ce4 f and4 d photoemission spectra, the resonance effect due to the Ce3 d 3/2 –4 f excitation is weaker than that due to the3 d 3/2 –4 f excitation. (2) At the3 d 3/2 –4 f threshold, three Auger structures appear at the higher binding energy side of the Ce4 d core level. (3) The intensity of the partial yield (photoemission intensity at 5 eV kinetic energy) is stronger at the3 d 3/2 –4 f excitation threshold than at the3 d 5/2 –4 f threshold. The origin of these features is discussed in terms of a Coster-Kronig decay channel (3 d 3/2 –3 d 5/2 4 f Auger transition) such as3 d 3/2 4 f →3 d 5/2 ɛ f (3d andɛ f denote a3 d core hole and a continuum f state, respectively). The occupation number of4 f electrons in CeOs 2 is estimated to be ∼0.75 from the analysis of the Ce3 d absorption spectrum.

High resolution Ce 4d → 4f resonance photoemission study was done for CeRu2Si2. The Ce 4f spectrum has shown two prominent peaks around 0.3 and 2.5 eV. The 0.3 eV peak has clearly shown an additional structure closer to the Fermi level, whose intensity decreases at higher temperatures. This intensity reduction is ascribed to the tail of the Kondo resonance peak.

We have studied vanadium oxides corresponding to formally 3 d 0 ( V 2 O 5 ), 3 d 1 ( VO 2 ), and 3 d 2 ( V 2 O 3 ) configurations and compare them with mixed valent Na 0.33 V 2 O 5 , using hard X-ray core level photoemission spectroscopy (PES), which enables to probe bulk electronic states due to large escape depth of high kinetic energy photoelectrons. The quasi-one-dimensional mixed-valence compound Na 0.33 V 2 O 5 and three-dimensional V 2 O 3 undergo metal–insulator (MI) transition at T MI = 135 and 160 K, respectively. The observed V 2 p core level spectra of V 2 O 5 and VO 2 show a single peak with chemical shifts corresponding to the V 5 + and V 4 + , while two components ( V 5 + and V 4 + ) are observed in Na 0.33 V 2 O 5 . Metallic V 2 O 3 shows a bulk character additional peak at low binding energy in the V 2 p core levels. We also study the V 1 s core level spectra of these compounds, which are possible only using hard X-rays and confirm the systematics in valence states of vanadium oxides. The temperature dependence of the low binding energy peak in V 1 s spectra across the MI transition in V 2 O 3 suggests an additional screening channel available in the Mott–Hubbard correlated metal phase.

In order to clarify the intrinsic bulk electronic structure of La1−xSrxMnO3 (LSMO) thin films, we have performed high-energy ( h ν = 5.95 keV) synchrotron photoemission spectroscopy (PES) of Mn 2p core-levels. In sharp contrast with the previous soft X-ray PES ( h ν = 800 –1486.6 eV), the high-energy PES spectra exhibit a clear additional peak at the low binding-energy side of the Mn 2 p 3 / 2 peak. To check for surface sensitivity, we measured take-off-angle dependence of Mn 2p core-levels. The results indicate that this additional peak originates from the bulk electronic structure. The peak shows a noticeable increase in the metallic phase of LSMO for x = 0.2 and 0.4, indicating that the origin of this peak is strongly related to the metallic physical properties of LSMO thin films. A single ion ( MO 6 ) cluster calculation including charge transfer from doping-induced states reproduces the new bulk-derived feature observed in Mn 2p core-levels.

We have realized hard X-ray (HX) photoemission spectroscopy (PES) with high throughput and high-energy resolution for core level and valence band studies using high-energy and high-brilliance synchrotron radiation at SPring-8. This is a brand new method because large escape depth of high-energy photoelectrons enables us to probe intrinsic bulk states free from surface condition. By use of a newly developed electron energy analyzer and well-focused X-rays, high-energy resolution of 75 meV ( E /Δ E = 79,000) was realized for 5.95 keV photoelectrons.

We report a photoemission spectroscopy study on IrTe2 which exhibits an interesting lattice distortion below 270 K. Ir 4f core-level photoemission spectrum is broadened in going from 300K to 40K. This result indicates the charge moderation of Ir 5d electrons. Angle-resolved photoemission spectroscopy(ARPES) result at 300K shows multi-band Fermi surfaces with six-fold symmetry which are basically consistent with band structure calculations. At the distorted phase, the inner Fermi surfaces become quasi one-dimensional Fermi surface due to the lattice distortion.

We have studied the low-energy electronic structure of a Kondo insulator YbB{sub 12} by high-resolution photoemission spectroscopy. A {open_quote}{open_quote}Kondo peak{close_quote}{close_quote} is observed {approximately}25 meV below the Fermi level, which agrees well with the Kondo temperature, whereas the gap at the Fermi level is found much smaller, indicating that the magnetic properties at higher temperatures (75 K) are indeed determined by the Kondo effect in spite of the gap formation at lower temperatures. A renormalized band picture is presented to describe the coexistence of the Kondo peak and the transport gap as well as the highly asymmetric line shape of the Kondo peak. {copyright} {ital 1996 The American Physical Society.}

Valence-band and conduction-band densities of states (DOSs) of trigonal and amorphous Se have been investigated by in situ measurements of ultraviolet photoemission and inverse-photoemission spectroscopies (UPS and IPES), respectively. The IPES spectra reveal, for the first time, a measure of conduction-band DOS, while the UPS spectra are fully consistent with earlier results. From comparison between theoretical DOS and a whole spectrum for trigonal Se obtained by a connection of the UPS and IPES spectra at the Fermi level, it has been shown that the coupling strength between the hybrid 4p-like orbitals of different atoms should be increased. On the basis of a comparison between IPES and core-absorption spectra for trigonal Se, a prominent peak and weak structures in the 1-5 and 5-10 eV regions above the valence-band maximum in the IPES spectrum are experimentally assigned to the 4p-like antibonding and 4d and/or 5s states, respectively. In amorphous Se, the peak at shallower energy in the 4p-like bonding bands with two peak structures is more intense in contrast to the case of the trigonal one. Such a change is attributed to a chain structure with the dihedral angle varying randomly in sign along the chain. Increases of the bonding-antibonding splitting energy of the 4p-like bands and band-gap energy in amorphous Se are ascribed to an increase of intrachain coupling strength between the hybrid 4p-like orbitals and a simultaneous decrease of the interchain coupling strength.

Electronic structures of Magneli-phase η- and γ-Mo4O11 have been studied by means of ultraviolet photoemission and inverse-photoemission spectroscopies. Resonant photoemission spectra have been also measured in the photon energy range from 32 eV to 90 eV The energy positions of Mo 4d states can be qualitatively explained in terms of a simple band structure model.

All solid state band-pass photon detectors for IPES have been developed. The detectors are composed of an optical filter for vacuum ultraviolet and a solar blind photomultiplier. A high resolution (∼0.3eV) and a high sensitivity were simultaneously realized by the best combination of elements, which are a KCl thin film, a CaF2 window and a solar-blind photomultiplier with a KCl deposited first dynode.

Electronic structures of Zn1−xMnxTe films (0 ≤ x ≤ 0.7) have been investigated by means of in situ measurements of inverse-photoemission and photoemission spectra. The Mn 3d spin-exchange splitting energy of 7.2 ± 0.2 eV is evaluated from emission peaks due to the Mn 3d↓ and 3d↑ states with eg symmetry. On the other hand, the whole spectrum including multielectron satellite compares well with the Mn 3d inverse-photoemission and photoemission spectra calculated using a configuration-interaction theory.

Valence-band and conduction-band electronic structures of MnY (Y=S, Se, Te) have been investigated by in situ measurements of photoemission and inverse-photoemission spectra. We find that the Mn 3d spin-exchange splitting energies increase as going from MnTe (6.6 eV) to MnSe (7.4 eV), and further to MnS (8.0 eV).

Hard x-ray valence band photoemission spectroscopy (PES) is realized using high-energy and high-brilliance synchrotron radiation. High-energy (∼6 keV) excitation results in larger probing depths of photoelectrons compared to conventional PES, and enables a study of intrinsic electronic property of materials in actual device structures much less influenced by surface condition. With this technique, requirements for surface preparation are greatly reduced, if not eliminated. It is a nondestructive tool to determine electronic structure from surface to genuine bulk as shown by a study on SiO2/Si(100). Electronic structure modification related to the ferromagnetism in the diluted magnetic semiconductor Ga0.96Mn0.04N is also observed.

Electronic structures of Zn1-xMnxTe films (0

Angle-resolved photoemission spectroscopy using tunable low energy photons allows us to study the quasi-particle (QP) dispersions of the inner and outer CuO2 planes (IP and OP) separately in the tri-layer cuprate Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$ (Bi2223). The kink energy of the OP band is $\sim$ 70 meV, as observed in various high-$T_c$ cuprates, while that of the IP band is as large as 100 meV in the superconducting (SC) state. This large kink energy is attributed to the $\sim$ 35 meV buckling mode plus the large ($\sim$ 60 meV) SC gap of IP. The IP band also shows a weak kink feature at 70 meV in the SC state. The latter feature can be explained either by the 70 meV half-breathing mode or by the $\sim$ 35 meV buckling-phonon mode plus the $\sim$ 40 meV SC gap of OP if interlayer scattering of QP is involved., Comment: 5 pages, 2 figures

We have performed a temperature dependent angle-resolved photoemission spectroscopy (ARPES) study of the tri-layer high-$T_c$ cuprate superconductor (HTSC) Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$ (Bi2223), and have shown that the \textquotedblleft effective\textquotedblright superconducting (SC) gap $\Delta_{\rm{sc}}$ defined at the end point of the Fermi arc and the $T_c$ (= 110 K) approximately satisfies the weak-coupling BCS-relationship 2$\Delta_{\rm{sc}}$ = 4.3$k_{\rm{B}}T_c$. Combining this result with previous ARPES results on single- and double-layer cuprates, we show that the relationship between 2$\Delta_{\rm{sc}}$ = 4.3$k_{\rm{B}}T_c$ holds for various HTSCs. Furthermore, at $T$ $\sim$ $T_c$, the quasi-patricle width at the end point of the Fermi arc is found to coincide with $\Delta_{\rm{sc}}$, consistent with the context of Planckian dissipation.

The experimental evidence is presented of the topological insulator state in PbBi2Te4. A single surface Dirac cone is observed by angle-resolved photoemission spectroscopy with synchrotron radiation. Topological invariants Z2 are calculated from the ab initio band structure to be 1;(111). The observed two-dimensional isoenergy contours in the bulk energy gap are found to be the largest among the known three-dimensional topological insulators. This opens a pathway to achieving a sufficiently large spin current density in future spintronic devices.

We report an angle-resolved photoemission spectroscopy study of BaFe2−xCoxAs2. For x=0, above the structural and magnetic transition temperature (Ts), the spectral weight near the Fermi level is considerably suppressed around the Γ point where the Fe 3d yz/zx orbital degeneracy is expected. This observation suggests that the Jahn–Teller type instability is playing an important role in the tetragonal phase above Ts. Below Ts, the spectral weight of 0–100 meV is reconstructed to form flat bands at 70–100 meV and Fermi surfaces, consistent with the orbital-dependent excitonic coupling. In the optimally doped and overdoped regimes, the hole pocket around the Γ point and the electron pocket around the M point are apparently nested, indicating that the doping dependence of the superconducting transition temperature cannot be explained by the nesting scenario and that the unusual electron–lattice fluctuation due to the orbital degeneracy is important.

We have investigated physical properties of the layered Mn oxypnictides (LaO)MnPn; Pn = P, As, Sb. Electrical resistivity of three samples, indicting semiconducting behaviors, drastically increases with lowering temperature. The optical band gaps estimated from the diffusive reflectance are about 1.6 eV and they don't depend on pnictogen atoms even though the lattice constants widely change. Magnetizations of (LaO)MnAs and (LaO)MnSb show very weak temperature dependence with positive slope against temperature. Some magnetic order is expected to exist at higher temperature than room temperature. Consequently, the Mn oxypnictides (LaO)MnPn are magnetic semiconductors.

Using polarization- and hν-dependent angle-resolved photoemission spectroscopy, we uncovered the fine details of a quasiparticle's dynamics of a typical multiband superconductor, Sr2RuO4. We found strong hybridization between the in-plane and out-of-plane quasiparticles via the Coulomb and spin-orbit interactions. This effect enhances the quasiparticle mass due to the inflow of out-of-plane quasiparticles into the two-dimensional Fermi surface sheet, where the quasiparticles are further subjected to the multiple electron-boson interactions. We suggest that the spin-triplet p-wave superconductivity of Sr2RuO4 is phonon mediated.

We report the first observation of a topological surface state on the (111) surface of the ternary chalcogenide TlBiSe₂ by angle-resolved photoemission spectroscopy. By tuning the synchrotron radiation energy we reveal that it features an almost ideal Dirac cone with the Dirac point well isolated from bulk continuum states. This suggests that TlBiSe₂ is a promising material for realizing quantum topological transport.

The three-dimensional band structure and superconducting gap of Ba0.6K0.4Fe2As2 are studied with angle-resolved photoemission spectroscopy. In contrast with previous results, we have identified three holelike Fermi surface sheets near the zone center with sizable out-of-plane or kz dispersion. The superconducting gap on certain Fermi surface sheets shows significant kz dependence. Moreover, the superconducting gap sizes are different at the same Fermi momentum for two bands with different spatial symmetries (one odd, one even). Our results further reveal the three-dimensional and orbital-dependent structure of the superconducting gap in iron pnictides, which facilitates the understanding of momentum-integrated measurements and provides a distinct test for theories.

We report the first observation of the multilayer band splitting in the optimally doped trilayer cuprate ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{10+\ensuremath{\delta}}$ (Bi2223) by angle-resolved photoemission spectroscopy. The observed energy bands and Fermi surfaces are originated from the outer and inner ${\mathrm{CuO}}_{2}$ planes (OP and IP). The OP band is overdoped with a large $d$-wave gap around the node of ${\ensuremath{\Delta}}_{0}\ensuremath{\sim}43\text{ }\text{ }\mathrm{meV}$ while the IP is underdoped with an even large gap of ${\ensuremath{\Delta}}_{0}\ensuremath{\sim}60\text{ }\text{ }\mathrm{meV}$. These energy gaps are much larger than those for the same doping level of the double-layer cuprates, which leads to the large ${T}_{c}$ in Bi2223. We propose possible origins of the large superconducting gaps for the OP and IP: (1) minimal influence of out-of-plane disorder and a proximity effect and (2) interlayer tunneling of Cooper pairs between the OP and IP.

We have determined the electron-coupling spectrum of superconducting Bi2Sr2CaCu2O(8+δ) from high-resolution angle-resolved photoemission spectra by two deconvolution-free robust methods. As hole concentration decreases, the coupling spectral weight at low energies ≲15 meV shows a twofold and nearly band-independent enhancement, while that around ∼65 meV increases moderately, and that in ≳130 meV decreases leading to a crossover of dominant coupling excitation between them. Our results suggest the competition among multiple screening effects, and provide important clues to the source of sufficiently strong low-energy coupling, λ(LE)≈1, in an underdoped system.

We have revealed the underlying mechanism of the martensitic phase transition (MPT) in a new class of ferromagnetic shape memory alloys, Ni2Mn1+xSn1-x, by the combination of bulk-sensitive hard-x-ray photoelectron spectroscopy and a first-principles density-functional calculation. The Ni 3d e{g} state in the cubic phase systematically shifts towards the Fermi energy with an increase in the number of Mn atoms substituted in the Sn sites. An abrupt decrease of the intensity of the Ni 3d e{g} states upon MPT for x=0.36-0.42 has been observed in the vicinity of the Fermi level. The energy shift of the Ni 3d minority-spin e{g} state in the cubic phase originates from hybridization with the antiferromagnetically coupled Mn in the Sn site. Below the MPT temperature, the Ni 3d state splits into two levels located below and above the Fermi energy in order to achieve an energetically stable state.