Research on partial electronic density of states in superoonducting diborides by x-ray absorption and emission spectroscopies

点击翻译按钮获取中文摘要

X-ray emission (XES) and obsorption (XAS) spectra near the B K-edge were measured on single-crystalline AlB2 which is an isostructural diboride of superconducting MgB2, and on single-crystalline MgB2. The partial density of states (PDOS) of B-2p-σ and p-π orbitals were derived from the polarization dependence of XES and XAS spectra.The overall features of PDOS were found to be in good agreement with the result of band calculation of AlB2 and MgB2. There are considerable amounts of PDOS near the Fermi energy in AlB2 similarly to that in MgB2, but there are almost no PDOS in p-σ orbitals of AlB2 near the Fermi energy, i.e., a pseudo-gap in p-σ state and a broad metallic state in p-π state are observed, On the contrary, there are considerable amount of PDOS in p-σ orbitals of MgB2 near the Fermi energy, i.e., broad metallic states in p-π state and p-σ state are observedThe present result indirectly supports scenarios that the p-σ holes play an important role in the occurrence of superconductivity in MgB2.The effect of electron correlation (EC) on the partial density of state (PDOS) were studied by the polarization dependence of x-ray emission and absorption spectra of MgB2, AlB2 single crystals.There are some discrepancies between the observed PDOSs and theoretical ones, although these are contrary to the electron-correlation effects. The present results suggest that the EC effect is less than the experimental error (0.2 eV), which indirectly supports a scenario that electron-phonon interaction plays an essential role in the occurrence of superconductivity.