We have investigated the doping and temperature dependences of the pseudogap and superconducting gap in the single-layer cuprate La2-xSrxCuO4 by angle-resolved photoemission spectroscopy. The results clearly exhibit two distinct energy and temperature scales, namely, the gap around (pi, 0) of magnitude Delta* and the gap around the node characterized by the d-wave order parameter Delta0. In comparison with Bi2212 having higher Tc's, Delta0 is smaller, while Delta* and T* are similar. This result suggests that Delta* and T* are approximately material-independent properties of a single CuO2 plane, in contrast to the material-dependent Delta0, representing the pairing strength.

The correlated electronic structure of SrVO(3) has been investigated by angle-resolved photoemission spectroscopy using in situ prepared thin films. Pronounced features of band renormalization have been observed: a sharp kink ∼60 meV below the Fermi level (E(F)) and a broad so-called "high-energy kink" ∼0.3 eV below E(F) as in the high-T(c) cuprates, although SrVO(3) does not show magnetic fluctuations. We have deduced the self-energy in a wide energy range by applying the Kramers-Kronig relation to the observed spectra. The obtained self-energy clearly shows a large energy scale of ∼0.7 eV, which is attributed to electron-electron interaction and gives rise to the ∼0.3 eV kink in the band dispersion as well as the incoherent peak ∼1.5 eV below E(F). The present analysis enables us to obtain a consistent picture for both the incoherent spectra and the band renormalization.

The nature of the pseudogap in high transition temperature (high-T c ) superconducting cuprates has been a major issue in condensed matter physics. It is still unclear whether the high-T c superconductivity can be universally associated with the pseudogap formation. Here we provide direct evidence of the existence of the pseudogap phase via angle-resolved photoemission spectroscopy in another family of high-T c superconductor, iron-pnictides. Our results reveal a composition dependent pseudogap formation in the multi-band electronic structure of BaFe 2 (As 1-x P x ) 2 . The pseudogap develops well above the magnetostructural transition for low x, persists above the nonmagnetic superconducting dome for optimal x and is destroyed for x ~ 0.6, thus showing a notable similarity with cuprates. In addition, the pseudogap formation is accompanied by inequivalent energy shifts in xz/yz orbitals of iron atoms, indicative of a peculiar iron orbital ordering which breaks the four-fold rotational symmetry.The pseudogap (PG) observed in the normal state of the high-T c copper oxide superconductors remains a mysterious state of matter [1][2][3]. It has been attributed to several mechanisms such as a precursor pairing [4][5][6] and a novel form of spin/charge ordering [7][8][9]. Nearly a quarter-century after the discovery of high-T c superconductivity [10], the PG phase is still extensively debated in the literature and no consensus has been reached regarding its origin. In order to gain further insights into the relationship between the high-T c superconductivity and the PG, the exploration of the PG phase in other high-T c superconductors is highly desired.Iron-pnictides [11] are another class of high-T c superconductors whose typical phase diagram is shown in Fig. 1(a). The parent compound shows stripe-type antiferromagnetic (AF) ordering at T N accompanying a lattice distortion from tetragonal to orthorhombic structure at T s [12]. In contrast to the parent cuprate which is an AF insulator, the parent pnictide is an AF metal. The electronic structure derived from multiple Fe 3d orbitals [13], consists typically of disconnected hole and electron Fermi surfaces (FSs), which undergo an electronic reconstruction across T N and T s [14,15]. In addition to spin fluctuations derived from the nesting between the disconnected FSs [16,17], orbital fluctuations are also a candidate for a driving force of electron pairing in iron-pnictides [18,19] AsP122 system shows quasi-two dimensional FSs above T N,s as shown in Fig. 2(a). Three hole-FSs (, , ) and two electron-FSs (, ) exist around the BZ center and the BZ corner, respectively ( Fig.2 (b)). SubstitutingAs ions by isovalent P ion causes reduction of the pnictogen height without changing the carrier density. As P ion concentration is increased, the warping of the -hole In order to investigate the T-dependence of the fine electronic structure in the multi-orbital system, it is required to clearly separate the multiple band dispersions.For this purpose, we chose p-polarization...

We have investigated orbital character and electron correlation effects on Fermi surfaces in the hole-overdoped iron pnictide superconductor KFe 2 As 2 , which shows a low T c of ∼4 K, by angle-resolved photoemission spectroscopy. From the polarization-dependence of the ARPES spectra, we have determined the orbital character of each Fermi surface. Electron mass renormalization of each band is quantitatively consistent with de Haas-van Alphen results. The outer β and middle ζ Fermi surfaces show large renormalization factor of m * /m b ∼6-7, while the inner α Fermi surface has a smaller factor m * /m b ∼2. Middle hole Fermi surface ζ has strong three-dimensionality compared to other Fermi surfaces, indicating the d 3z2−r2 orbital character, which may be related to the "octet-line nodes" recently observed by laser ARPES. The observed orbital-dependent mass renormalization would give constraints on the pairing mechanism with line nodes of this system.

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