Elastic scattering susceptibility of the high temperature superconductor Bi2Sr2CaCu2O(8+delta): a comparison between real and momentum space photoemission spectroscopies

The joint density of states of Bi2Sr2CaCu2O(8+delta) is calculated by evaluating the autocorrelation of the single particle spectral function A(k, omega) measured from angle resolved photoemission spectroscopy (ARPES). These results are compared with Fourier transformed (FT) conductance modulations measured by scanning tunneling microscopy (STM). Good agreement between the two experimental probes is found for two different doping values examined. In addition, by comparing the FT-STM results to the autocorrelated ARPES spectra with different photon polarization, new insight on the form of the STM matrix elements is obtained. This shines new light on unsolved mysteries in the tunneling data.     

Surface electronic structure of single-domain Si( 001) 2 × 2-Al: an angle-resolved photoelectron spectroscopy study using synchrotron radiation

The electronic structure of a single-domain Si(001)2 × 2-Al surface has been studied by angle-resolved photoelectron spectroscopy (ARPES) using synchrotron radiation. Through detailed ARPES measurements along various symmetry axes of the surface Brillouin zone, the existence and dispersions of five surface states are identified, one at binding energies a little less than 1 eV and the others between 1 and 2 eV. The origin of the surface states are discussed in terms of the Al-dimer structures on Si(001).     

Effect of Zn and Ni impurities on the quasiparticle renormalization of superconducting Bi-2212

The Cu substitution by Zn and Ni impurities and its influence on the mass renormalization effects in angle-resolved photoelectron spectra (ARPES) of Bi2Sr2CaCu2O8-delta is addressed. We show that the nonmagnetic Zn atoms have a much stronger effect in both the nodal and antinodal parts of the Brillouin zone than magnetic Ni. The observed changes are consistent with the behavior of the spin resonance mode as seen by inelastic neutron scattering in YBCO. This strongly suggests that the "peak-dip-hump" and the kink in ARPES on the one side and neutron resonance on the other are closely related features.     

Fermi surface of Bi2Sr2CaCu2O8

We study the Fermi surface of Bi2Sr2CaCu2O8 using angle resolved photoemission spectroscopy (ARPES) with a momentum resolution of approximately 0.01 of the Brillouin zone. We show that, contrary to recent suggestions, the ARPES derived Fermi surface is a large hole barrel centered at (pi,pi), independent of the incident photon energy. We caution that the photon energy and k dependence of the matrix elements, if not properly accounted for, can lead to misinterpretation of ARPES intensities.     

Crossover from coherent to incoherent electronic excitations in the normal state of Bi(2)Sr(2)CaCu(2)O(8+delta)

Angle resolved photoemission spectroscopy (ARPES) and resistivity measurements are used to explore the overdoped region of the high temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+delta). We find evidence for a new crossover line in the phase diagram between a coherent metal phase, for lower temperatures and higher doping, and an incoherent metal phase, for higher temperatures and lower doping. The former is characterized by two well-defined spectral peaks in ARPES due to coherent bilayer splitting and superlinear behavior in the resistivity, whereas the latter is characterized by a single broad spectral feature in ARPES and a linear temperature dependence of the resistivity.     

Fermi surface, surface states, and surface reconstruction in Sr2RuO4

The electronic structure of Sr2RuO4 is investigated by high angular resolution ARPES at several incident photon energies. We address the controversial issues of the Fermi surface (FS) topology and the van Hove singularity at the M point, showing that a surface state and the replica of the primary FS due to sqrt[2]xsqrt[2] surface reconstruction are responsible for previous conflicting interpretations. The FS thus determined by ARPES is consistent with the de Haas-van Alphen results, and it provides additional information on the detailed shape of the alpha, beta, and gamma sheets.     

Properties of hydrogen terminated diamond as a photocathode

Electron emission from the negative electron affinity (NEA) surface of hydrogen terminated, boron doped diamond in the [100] orientation is investigated using angle resolved photoemission spectroscopy (ARPES). ARPES measurements using 16 eV synchrotron and 6 eV laser light are compared and found to show a catastrophic failure of the sudden approximation. While the high energy photoemission is found to yield little information regarding the NEA, low energy laser ARPES reveals for the first time that the NEA results from a novel Franck-Condon mechanism coupling electrons in the conduction band to the vacuum. The result opens the door to the development of a new class of NEA electron emitter based on this effect.     

铜氧化物超导体Bi2Sr2CaCu2O8+δ 多体相互作用的超高能量分辨和时间分辨 角分辨光电子能谱研究

自发现30 多年来,铜氧化物的高温超导机理仍未得到解释。传统超导电性起源于电 子–声子相互作用形成的电子配对,研究传统超导体中的多体相互作用为BCS 理论提供了有 力的证据。目前已证实铜氧化物高温超导体中存在着电子配对,但是引起配对的机制仍不清 楚。因此,对铜氧化物高温超导体中的多体相互作用研究是揭示高温超导机理的关键。角分辨 光电子能谱是研究固体电子结构最直接的技术手段,随着其分辨率的不断提升,在研究高温超 导体的多体相互作用中日益发挥重要的作用。近年来兴起的时间分辨角分辨光电子能谱在常规 角分辨光电子能谱的基础上增加了独特的时间维度,从而成为研究多体相互作用动力学的有力 手段。本文详细地介绍了我们利用超高能量分辨和时间分辨角分辨光电子能谱在铜氧化物超导 体Bi2Sr2CaCu2O8+δ 中多体相互作用的研究,包括在节点区域、反节点区域扭折的研究,多体 相互作用的动量依赖关系,配对电子自能的提取以及库珀对在激光泵浦下的受激辐射现象。     

Bridging charge-orbital ordering and Fermi surface instabilities in half-doped single-layered manganite La(0.5)Sr(1.5)MnO₄

The single-layered half-doped manganite La(0.5)Sr(1.5)MnO? (LSMO), was studied by means of the angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM), and resistivity measurements. STM revealed a smooth reconstruction-free surface; the density of states, extracted from photoemission and tunneling spectroscopy, is in agreement with transport measurements. The derived from ARPES Fermi surface (FS) nesting properties correspond to the known pattern of the charge-orbital ordering (COO), which implies that FS instability is related to the propensity to form a COO state in LSMO.     

Angle-resolved photoemission spectroscopy study of the (101) surface of the Kondo insulator CeNiSn

The electronic structure of CeNiSn, which is considered a possible topological Kondo insulator, has been investigated by employing synchrotron radiation excited angle-resolved photoemission spectroscopy (ARPES). We have found that the easy cleavage plane in CeNiSn is (101), for which we have investigated the Fermi surface (FS) and band structures. The measured FS and ARPES for the (101) plane are described well by the calculated FS and band structures, obtained from the DFT calculations. The measured ARPES bands and photon energy map show that the metallic states crossing the Fermi level have the 3D nature, casting a negative suspicion for the existence of the topological surface states of the 2D character in CeNiSn. The Ce 4f Kondo resonance peak is observed in Ce 4d → 4f resonant photoemission spectroscopy, suggesting the importance of the Ce 4f electrons in determining the temperature-dependent topological electronic structure of CeNiSn.     

Low energy excitation and scaling in Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4) (n=1-3): angle-resolved photoemission spectroscopy

Angle-resolved photoemission spectroscopy (ARPES) has been performed on the single- to triple-layered Bi-family high-T (c) superconductors (Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4), n=1-3). We found a sharp coherent peak as well as a pseudogap at the Fermi level in the triple-layered compound. Comparison among three compounds has revealed a universal rule that the characteristic energies of superconducting and pseudogap behaviors are scaled with the maximum T (c).     

Dopant-induced nanoscale electronic inhomogeneities in Ca(2-x)Sr(x)RuO4

Ca(2-x)Sr(x)RuO4 single crystals with 0.1 < or = x < or = 2.0 have been studied systematically using scanning tunneling microscopy (STM) and spectroscopy, low-energy electron diffraction, and angle resolved photoelectron spectroscopy (ARPES). In contrast with the well-ordered lattice structure, the local density of states at the surface clearly shows a strong doping dependent nanoscale electronic inhomogeneity, regardless of the fact of isovalent substitution. Remarkably, the surface electronic roughness measured by STM and the inverse spectral weight of quasiparticle states determined by ARPES are found to vary with x in the same manner as the bulk in-plane residual resistivity, following the Nordheim rule. For the first time, the surface measurements--especially those with STM--are shown to be in good agreement with the bulk transport results, all clearly indicating a doping-induced electronic disorder in the system.     

Strong and complex electron-lattice correlation in optimally doped Bi2Sr2CaCu2O8+delta

We discuss the nature of electron-lattice interaction in optimally doped Bi_{2}Sr_{2}CaCu_{2}O_{8+delta} samples, using the isotope effect (IE) in angle resolved photoemission spectroscopy (ARPES) data. The IE in the ARPES linewidth and the IE in the ARPES dispersion are both quite large, implying a strong electron-lattice correlation. The strength of the electron-lattice interaction is "intermediate," i.e., stronger than the Migdal-Eliashberg regime but weaker than the small polaron regime, requiring a more general picture of the ARPES kink than the commonly used Migdal-Eliashberg picture. The two IEs also imply a complex interaction, due to their strong momentum dependence and their differing sign behaviors. In sum, we propose an intermediate-strength coupling of electrons to localized lattice vibrations via charge density fluctuations.     

Chemical Structure of HfO2/Si Interface with Angle-Resolved Synchrotron Radiation Photoemission Spectroscopy

Interracial chemical structure of HfO2/Si （100） is investigated using angle-resolved synchrotron radiation photoemission spectroscopy （ARPES）. The chemical states of Hf show that the Hf 4f binding energy changes with the probing depth and confirms the existence of Hf-Si-O and Hf Si bonds. The Si 2p spectra are taken to make sure that the interracial structure includes the Hf silicates, Hf silicides and SiOx. The metallic characteristic of the Hf-Si bonds is confirmed by the valence band spectra. The depth distribution model of this interface is established.     

Soft X-ray ARPES and Fermiology of strongly correlated electron systems and PES by hard X-ray and extremely low energy photons

Bulk sensitivity is inevitable for photoelectron spectroscopy (PES) when one studies bulk electronic structures of strongly correlated electron systems, which are often much different from surface electronic structures. Combination of soft and hard X-ray PES (SXPES and HAXPES) is a promising approach for this purpose by quantitatively evaluating the contribution of the surface in the observed angle integrated PES spectra. Even in the angle resolved PES studies (ARPES), the bulk sensitivity of the SX-ARPES is required to get the real bulk band dispersions and Fermi surface topology, which may be noticeably modified in the surface region as seen in several materials studied in this paper.Although hard X-ray ARPES is feasible, deep attention is required for the discussion of the possible recoil effects for the valence band. Besides, extremely low energy PES (ELEPES) by use of microwave excited Xe, Kr and Ar lamps will be as useful as those by synchrotron radiation and laser to realize a very high resolution of better than 5 meV with bulk sensitivity under certain conditions.     

Existence, character, and origin of surface-related bands in the high temperature iron pnictide superconductor BaFe(2-x)Co(x)As2

Low energy electron diffraction (LEED) experiments, LEED simulations, and finite slab density functional calculations are combined to study the cleavage surface of Co doped BaFe(2-x)Co(x)As2 (x = 0.1,0.17). We demonstrate that the energy dependence of the LEED data can only be understood from a terminating 1/2 Ba layer accompanied by distortions of the underlying As-Fe2-As block. As a result, surface-related Fe 3d states are present in the electronic structure, which we identify in angle resolved photoemission spectroscopy (ARPES) experiments. The close proximity of the surface-related states to the bulk bands inevitably leads to broadening of the ARPES signals, which excludes the use of the BaFe(2-x)Co(x)As2 system for accurate determination of self-energies using ARPES.     

Polarization dependence of angle-resolved photoemission spectroscopy of graphite

We have used variable polarization synchrotron radiation to map the valence band electronic structure of graphite by angle-resolved photoemission spectroscopy (ARPES). The experimental results with two orthogonal linear polarization of light signifies the contribution of either even or odd symmetry with respect to the crystal mirror plane towards the photoemission intensity. The σ₁ and σ₂ valence bands show odd reflection symmetry while the π valence band shows even symmetry with respect to the mirror plane. The measured ARPES spectrum using left and right circular polarized lights shows asymmetry in intensity around M point of the Brillouin zone, which ultimately mimicking different partial wave character of σ₁ and σ₃ bands.     

Electronic structure and anomalous photoemission line-shape of quasi-2D oxide η-Mo4O11

The η-Mo₄O₁₁ compound is a layered two-dimensional (2D) metallic system whose reduced dimensionality originates non-linear properties as charge density wave (CDW) instabilities. We report on synchrotron radiation angle resolved photoemission spectroscopy (ARPES) measurements in order to obtain a detailed picture of the electronic structure of this material. The symmetry of the states near the Fermi level (E_F) has been discussed in relation to the photoemission symmetry selections rules. Our results are in excellent agreement with previous tight-binding calculations and support the hidden nesting concept proposed to explain the CDW instabilities exhibited by this family of compounds. In addition, a very peculiar photoemission line-shape has been found with the presence of localized non-dispersive states. Some possible explanations are discussed.     

Bulk vs. surface effects in ARPES experiment from La2/3Sr1/3MnO3 thin films

Experiments directly probing the electronic states using angle-resolved photoemission (ARPES) were carried out on La_2/3Sr_1/3MnO₃ in order to elucidate its electronic properties. ARPES is a surface sensitive technique where bulk and surface states are usually both present. We present high-resolution ARPES studies in the (1 0 0) and (1 1 0) mirror planes and compare them with simulated ARPES based on GGA + U band structure calculations. In the (1 1 0) mirror plane we identify surface umklapps accounted by surface reconstruction which couple to bulk electronic states. As predicted by the simulated spectra there is additional spectral intensity at the Fermi level detected in ARPES data due to k_⊥-broadening effects in the photoemission final states. We demonstrate that this additional spectral intensity is a convenient spectral marker for determination of the k_F Fermi momenta.     

Remarks on the order parameter of the cuprate high temperature superconductors

A large body of spectroscopic data on the cuprate high temperature superconductors (CHTSC) is reviewed in order to determine their order parameter. ASJ, INS, B_2g Raman spectra, optical data, NIS “dips”, ARPES “dips” and ARPES “kinks” all show the same excitation energy (40 meV for OP95 systems), proportional to the superconducting transition temperature, and it is therefore identified with the order parameter.