Coupling between electrons and phonons (lattice vibrations) drives the formation of the electron pairs responsible for conventional superconductivity 1 . The lack of direct evidence for electron-phonon coupling in the electron dynamics of the high transition temperature superconductors has driven an intensive search for an alternative mechanism. A coupling of an electron with a phonon would result in an abrupt change of its velocity and scattering rate near the phonon energy. Here we use angle resolved photoemission spectroscopy to probe electron dynamicsvelocity and scattering rate-for three different families of copper oxide superconductors. We see in all of these materials an abrupt change of electron velocity at 50-80meV, which we cannot explain by any known process other than to invoke coupling with the phonons associated with the movement of the oxygen atoms. This suggests that electron-phonon coupling strongly influences the electron dynamics in the high-temperature superconductors, and must therefore be included in any microscopic theory of superconductivity. We investigated the electronic quasiparticle dispersions in three different families of hole-doped cuprates, Bi 2 Sr 2 CaCu 2 O 8 (Bi2212) and Pb doped Pb-Bi2212, Pb-doped Bi 2 Sr 2 CuO 6 (Pb-Bi2201) and La 2-x Sr x CuO 4 (LSCO). Except for the Bi2201 (overdoped, T c =7K) data and that in Fig. 3b, recorded at the beam-line 5.4 of the Stanford Synchrotron Radiation Laboratory (SSRL), all the data were recorded at the Advanced Light Source (ALS), as detailed elsewhere 2 . The top panels of figure 1 report the momentum distribution curve (MDC) derived dispersions along the (0, 0)-(π, π) direction for LSCO (panel a) and Bi2212 (panel b) superconducting state and for Pb-Bi2201 normal state (panel c) vs the rescaled momentum, k ' , defined by normalizing to one the momentum k relative to the Fermi momentum k F , (k-k F ), at the binding energy E=170meV. A "kink" in the dispersion around 50-80meV, highlighted by thick arrows in the figure, is the many-body effect of

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Quasiparticle dispersion in Bi2Sr2CaCu2O8 is investigated with improved angular resolution as a function of temperature and doping. Unlike the linear dispersion predicted by the band calculation, the data show a sharp break in dispersion at 50+/-15 meV binding energy where the velocity changes by a factor of 2 or more. This change provides an energy scale in the quasiparticle self-energy. This break in dispersion is evident at and away from the d-wave node line, but the magnitude of the dispersion change decreases with temperature and with increasing doping.

The electronic structure of heavily overdoped Bi2Sr2CaCu2O 8+δ is investigated by angle-resolved photoemission spectroscopy. The long-sought bilayer band splitting in this two-plane system is observed in both normal and superconducting states, which qualitatively agrees with the bilayer Hubbard model calculations. The maximum bilayer energy splitting is about 88 meV for the normal state feature, while it is only about 20 meV for the superconducting peak. This anomalous behavior cannot be reconciled with the quasiparticle picture.PACS numbers: 71.18.+y, 74.72.Hs, 79.60.Bm High temperature superconductors (HTSC's), as doped Mott insulators, show strong doping dependent behavior. The underdoped regime of the HTSC's is characterized by its unconventional properties, such as the pseudogap and non-Fermi liquid transport behavior. On the other hand, the overdoped regime is considered to be more "normal", partly because of the absence of a pseudogap and more Fermi liquid-like behavior. It is very challenging and important for HTSC theories to be able to explain the phenomenology in both regimes. Angle resolved photoemission spectroscopy (ARPES), one of the most direct probes of the electronic structure, has contributed greatly to the understanding of the electronic structure of the HTSC's. However, most systems studied by ARPES have either low T c 's (below 40K for La 2−x Sr x CuO 4+δ (LSCO), and Bi 2 Sr 2 CuO 6+δ (Bi2201)), or doping limitations (only up to slightly overdoping for Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) and YBa 2 Cu 3 O 7−y (YBCO)). For a complete understanding, it is very important to study the heavily overdoped systems, especially Bi2212, which is the most studied system by ARPES.Recent advances in high pressure annealing techniques have made it possible to synthesize heavily overdoped Bi2212. In this paper, we report ARPES measurements of the electronic structure of heavily overdoped Bi2212. We show that the long-sought bilayer band splitting (BBS) exists for both normal and superconducting states of this material over large fraction of the Brillouin zone. The detection of the BBS, which has been predicted by band structure calculations [1,2], but not observed in earlier ARPES data [3], enables us to address several important issues. First, it provides a very detailed test for the theoretical calculations, with our experimental results favoring the bilayer Hubbard model [4] over LDA calculations [1,2]. Second, it shows the novel result that the bilayer splitting energy in the superconducting state is only about 23% of the normal state splitting. Third, it provides an explanation for the detection of a "peak-diphump" structure in the normal state of heavily overdoped samples [5,6].Heavily overdoped Bi2212 samples (T C (onset) = 65 K, ∆T C (10% ∼ 90%) = 3 K, denoted as OD65) were synthesized by annealing floating-zone-grown single crystals under oxygen pressure P O2 = 300 atm at 300• C for two weeks, and characterized by various techniques. Magnetic susceptibility measurements show that the presence of a s...

A new layered oxypnictide (Fe 2 P 2 )(Sr 4 Sc 2 O 6 ) have been synthesized by solid-state reaction. This material has an alternating layer stacking structure of anti-fluorite Fe 2 P 2 and perovskite-based Sr 4 Sc 2 O 6 oxide layers. Space group of the material is P4/nmm and lattice constants a and c are 4.016 Å and 15.543 Å, respectively. The interlayer Fe-Fe distance corresponding to the c-axis length is the longest ever reported in the iron-based oxypnictide systems. In both magnetization and resistivity measurements, the present compound exhibited superconductivity below 17 K, which is much higher than that of LaFePO and the highest in arsenic-free iron-based oxypnictide systems under ambient pressure.