Novel electronic structure induced by a highly strained oxide interface with incommensurate crystal fields

The misfit oxide, Bi$_{2}$Ba$_{1.3}$K$_{0.6}$Co$_{2.1}$O$_{y}$, made of alternating rocksalt-structured [BiO/BaO] layers and hexagonal CoO$_{2}$ layers, was studied by angle-resolved photoemission spectroscopy. Detailed electronic structure of such a highly strained oxide interfaces is revealed for the first time. We found that under the two incommensurate crystal fields, electrons are confined within individual sides of the interface, and scattered by umklapp scattering of the crystal field from the other side. In addition, the high strain on the rocksalt layer raises its chemical potential and induces large charge transfer to the CoO$_{2}$ layer. Furthermore, a novel interface effects, the interfacial enhancement of electron-phonon interactions, is discovered. Our findings of these electronic properties lay a foundation for designing future functional oxide interfaces.

Doping-insensitive density-of-states suppression in polycrystalline iron-based superconductor SmO$_{1-x}$F$_{x}$FeAs

We investigated the temperature dependence of the density-of-states in the iron-based superconductor SmO_1-xF_xFeAs (x=0, 0.12, 0.15, 0.2) with high resolution angle-integrated photoemission spectroscopy. The density-of-states suppression is observed with decreasing temperature in all samples, revealing two characteristic energy scales (10meV and 80meV). However, no obvious doping dependence is observed. We argue that the 10meV suppression is due to an anomalously doping-independent normal state pseudogap, which becomes the superconducting gap once in the superconducting state; and alert the possibility that the 80meV-scale suppression might be an artifact of the polycrystalline samples.

Angle integrated photoemission study of SmO$_{0.85}$F$_{0.15}$FeAs

The electronic structure of the new superconductor, SmO$_{1-x}$F$_x$FeAs ($x=0.15$), has been studied by angle-integrated photoemission spectroscopy. Our data show a sharp feature very close to the Fermi energy, and a relative flat distribution of the density of states between 0.5 eV and 3 eV binding energy, which agrees best with band structure calculations considering an antiferromagnetic ground state. No noticeable gap opening was observed at 12 Kelvin below the superconducting transition temperature, indicating the existence of large ungapped regions in the Brillouin zone.