Effect of electron-phonon coupling in the ARPES spectra of the tri-layer cuprate Bi2_2Sr2_2Ca2_2Cu3_3O10+δ_{10+\delta}

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 figure

An energy scale directly related to superconductivity in the high-TcT_c cuprate superconductors: Universality from the Fermi arc picture

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.Comment: 5 pages, 4 figure

Energy-Dependent Enhancement of the Electron-Coupling Spectrum of the Underdoped Bi2Sr2CaCu2O8+d Superconductor

We have determined the electron-coupling spectrum of superconducting Bi2Sr2CaCu2O8+d 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, {\lambda}LE ~ 1, in underdoped system

Orbital Degeneracy and Peierls Instability in Triangular Lattice Superconductor Ir1−x_{1-x}Ptx_xTe2_2

We have studied electronic structure of triangular lattice Ir$_{1-x}$Pt$_x$Te$_2$ superconductor using photoemission spectroscopy and model calculations. Ir $4f$ core-level photoemission spectra show that Ir $5d$ $t_{2g}$ charge modulation established in the low temperature phase of IrTe$_2$ is suppressed by Pt doping. This observation indicates that the suppression of charge modulation is related to the emergence of superconductivity. Valence-band photoemission spectra of IrTe$_2$ suggest that the Ir $5d$ charge modulation is accompanied by Ir $5d$ orbital reconstruction. Based on the photoemission results and model calculations, we argue that the orbitally-induced Peierls effect governs the charge and orbital instability in the Ir$_{1-x}$Pt$_x$Te$_2$.Comment: 5 pages,4 figure

Electronic structure reconstruction by orbital symmetry breaking in IrTe2

We report an angle-resolved photoemission spectroscopy (ARPES) study on IrTe2 which exhibits an interesting lattice distortion below 270 K and becomes triangular lattice superconductors by suppressing the distortion via chemical substitution or intercalation. ARPES results at 300 K show multi-band Fermi surfaces with six-fold symmetry which are basically consistent with band structure calculations. At 20 K in the distorted phase, whereas the flower shape of the outermost Fermi surface does not change from that at 300 K, topology of the inner Fermi surfaces is strongly modified by the lattice distortion. The Fermi surface reconstruction by the distortion depends on the orbital character of the Fermi surfaces, suggesting importance of Ir 5d and/or Te 5p orbital symmetry breaking.Comment: 4pages, 4figure

Important Roles of Te 5p and Ir 5d Spin-orbit Interactions on the Multi-band Electronic Structure of Triangular Lattice Superconductor Ir1-xPtxTe2

We report an angle-resolved photoemission spectroscopy (ARPES) study on a triangular lattice superconductor Ir$_{1-x}$Pt$_{x}$Te$_2$ in which the Ir-Ir or Te-Te bond formation, the band Jahn-Teller effect, and the spin-orbit interaction are cooperating and competing with one another. The Fermi surfaces of the substituted system are qualitatively similar to the band structure calculations for the undistorted IrTe$_2$ with an upward chemical potential shift due to electron doping. A combination of the ARPES and the band structure calculations indicates that the Te $5p$ spin-orbit interaction removes the $p_x/p_y$ orbital degeneracy and induces $p_x \pm ip_y$ type spin-orbit coupling near the A point. The inner and outer Fermi surfaces are entangled by the Te $5p$ and Ir $5d$ spin-orbit interactions which may provide exotic superconductivity with singlet-triplet mixing.Comment: 10 pages, 4 figure