Electron-like Sheets Research Articles

Angle-resolved photoemission study of Sr 2RuO 4; An extended van-Hove singularity in non-cuprate superconductor

We have performed high-resolution angle-resolved photoemission spectroscopy of a non-cuprate layered superconductor Sr 2RuO 4 to study the electronic structure near the Fermi level ( E F). The result shows an extended van Hove singularity (vHs) along the RuO bonding direction just like the cuprate, regardless of the character of the electronic states at E F. This suggests that the extended vHs is a general electronic structure of a two dimensional correlated d-electron metal. We also have found that the observed Fermi surface topology (one electron-like Fermi surface sheet centered at Γ point and two hole-like ones centered at X point) is qualitatively different from the calculated Fermi surface topology (two electron-like Fermi sheets centered at Γ point and one hole-like one centered at X point) in the consequence of the existence of the vHs.

Angle-resolved photoemission spectroscopy of non-cuprate two-dimensional perovskite superconductor Sr 2RuO 4

We have performed high-resolution angle-resolved photoemission spectroscopy on single crystal Sr 2RuO 4 at low temperature. We observed that the dispersion of energy bands near the Fermi level ( E F) is about two times smaller than the band calculation. One band forms an extended van-Hove singularity (vHs) near E F around the midpoint between γ and Z point like in cuprate superconductors, regardless of the character of electronic states near E F. The observed Fermi surface topology (one electron-like Fermi surface sheet centered at γ point and two hole-like ones centered at X point) is qualitatively different from the calculated Fermi surface topology (two electron-like fermi sheets centered at γ point and one hole-like one centered at X point), though the observed total electron count seems to be conserved. These results suggest that the extended vHs may be a general electronic structure of correlated two-dimensional metals and the correlation effect may change the Fermi surface topology as well as the band dispersion.

Angle-resolved photoemission study of Sr2RuO4.

We present high-resolution (HR) angle-resolved photoemission spectroscopy (ARPES) measurements of the noncuprate layered perovskite superconductor ${\mathrm{Sr}}_{2}$${\mathrm{RuO}}_{4}$. ARPES spectra of the whole valence-band region obtained along two high-symmetry directions in the Brillouin zone show clear dispersion, generally similar to that of a band calculation. However, HRARPES measurements taken in the vicinity of the Fermi level (${\mathit{E}}_{\mathit{F}}$) show narrower Ru4d\ensuremath{\varepsilon}(xy,yz,zx)-O2p\ensuremath{\pi} antibonding bands than those predicted by the band calculation. More significantly, there is an extended van Hove singularity very close to ${\mathit{E}}_{\mathit{F}}$ (${\mathit{E}}_{\mathit{B}}$=11 meV) along the Ru-O bonding direction, which is known to exist in cuprate high-temperature superconductors. The Fermi-surface topology obtained by HRARPES (one electronlike Fermi surface sheet centered at the \ensuremath{\Gamma} point and two holelike sheets centered at the X point) is different from the band calculation (two electronlike sheets centered at the \ensuremath{\Gamma} point and one holelike sheet centered at the X point), although the electron count is the same in both cases. These results suggest that electron-electron correlations cause the modification of the Fermi-surface topology, and is thus necessary for understanding the electronic structure and properties of ${\mathrm{Sr}}_{2}$${\mathrm{RuO}}_{4}$. \textcopyright{} 1996 The American Physical Society.

Relationship of Sr2RuO4 to the superconducting layered cuprates.

The properties of ${\mathrm{Sr}}_{2}$${\mathrm{RuO}}_{4}$ are discussed in relation to the high-critical-temperature cuprate superconductors. The discussion is based on local-density-approximation band structure and phonon calculations. The electronic structure is highly anisotropic. Three hybridized Ru 4d--plane O p bands cross the Fermi energy, yielding cylindrical sheets of Fermi surface. Two of these are electronlike sheets around \ensuremath{\Gamma}, while the third is an X-centered hole surface. The electronlike sheets change topology as the energy is raised leading to Van Hove singularities in close proximity to the Fermi energy. In general, the electronic properties are related to those of the cuprates, with the exception that Coulomb correlations are expected to be much less significant due to the larger bandwidth and smaller on-site energy. ${\mathrm{Sr}}_{2}$${\mathrm{RuO}}_{4}$ is expected to be a very useful reference material for interpreting experiments on the cuprate superconductors.