We investigated electronic structure of 5d transition-metal oxide Sr 2 IrO 4 using angle-resolved photoemission, optical conductivity, and x-ray absorption measurements and first-principles band calculations. The system was found to be well described by novel effective total angular momentum J eff states, in which relativistic spin-orbit (SO) coupling is fully taken into account under a large crystal field. Despite of delocalized Ir 5d states, the J eff -states form so narrow bands that even a small correlation energy leads to the J eff = 1/2 Mott ground state with unique electronic and magnetic behaviors, suggesting a new class of the J eff quantum spin driven correlated-electron phenomena.

We have performed high resolution angle-resolved photoemission (ARPES) studies on electron-doped cuprate superconductors Sm2-xCexCuO4 (x=0.10, 0.15, 0.18), Nd2-xCexCuO4 (x=0.15), and Eu2-xCexCuO4 (x=0.15). Imaginary parts of the electron removal self energy show steplike features due to an electron-bosonic mode coupling. The steplike feature is seen along both nodal and antinodal directions but at energies of 50 and 70 meV, respectively, independent of the doping and rare earth element. Such energy scales can be understood as being due to preferential coupling to half- and full-breathing mode phonons, revealing the phononic origin of the kink structures. Estimated electron-phonon coupling constant lambda from the self energy is roughly independent of the doping and momentum. The isotropic nature of lambda is discussed in comparison with the hole-doped case where a strong anisotropy exists.

Angle resolved photoemission (ARPES) data from the electron doped cuprate superconductor Sm1.86Ce0.14CuO4 shows a much stronger pseudo-gap or "hot-spot" effect than that observed in other optimally doped n-type cuprates. Importantly, these effects are strong enough to drive the zone-diagonal states below the chemical potential, implying that d-wave superconductivity in this compound would be of a novel "nodeless" gap variety. The gross features of the Fermi surface topology and low energy electronic structure are found to be well described by reconstruction of bands by a √ 2× √ 2 order. Comparison of the ARPES and optical data from the same sample shows that the pseudo-gap energy observed in optical data is consistent with the inter-band transition energy of the model, allowing us to have a unified picture of pseudo-gap effects. However, the high energy electronic structure is found to be inconsistent with such a scenario. We show that a number of these model inconsistencies can be resolved by considering a short range ordering or inhomogeneous state.PACS numbers: 74.25. Jb, In spite of their many interesting physical properties 1,2,3,4 , electron-doped HTSCs have been much less studied as compared to the hole-doped HTSCs. It was not until a few years ago that high resolution ARPES was applied and there are still only a handful of published papers on the subject. In their high resolution ARPES studies, Armitage et al. found that for the highest T c samples of Nd 1.85 Ce 0.15 CuO 4 (NCCO) the near E F spectral weight was strongly suppressed at the momentum space positions where the underlying Fermi surface (FS) contour crosses the AF Brillouin zone boundary (AFZB) suggesting the existence of a (π,π) scattering channel 5 . It was also found that for (x=0.04) underdoped samples an electron FS pocket exists around (π,0) point and that at higher dopings spectral weight increases near (π/2,π/2) which eventually completes the large hole-like FS pocket around the (π,π) point 6 . A possible way to view the results for the highest-T c samples -at least qualitatively -is as a manifestation of a band reconstruction from a √ 2 × √ 2 static (or slowly fluctuating) spin density wave (SDW) or similar symmetry order 7 . Such a picture explains hot spots on the FS contour as due not to the opening of a 'pseudo-gap' per se but instead due to a band folding and then splitting across the AFZB giving FS pockets around (π/2, π/2) and (π, 0). Such a simple two band interpretation enables one to understand issues such as the sign change in the Hall coefficient 8 and optical conductivity 9 spectra. However, systematic studies to test the model are lacking and there may be doubts that such a simple picture could describe the data at the level of small details.Motivated by these issues, we have performed an extensive high resolution ARPES study on another compound in the small family of electron-doped HTSCs Sm 1.85 Ce 0.15 CuO 4 (SCCO) as well as optical reflection measurements. A quantitative analysis yields a number of important observat...

No abstract

No abstract