Electron energy-loss and soft X-ray emission spectroscopy of electronic structure of MgB₄

The electronic structure of MgB₄, with the characteristic crystal structure comprising one-dimensional pentagonal B₆ cluster chain, was investigated using electron energy-loss spectroscopy and soft X-ray emission spectroscopy based on transmission electron microscopy. The dielectric function and density of state of unoccupied and occupied states were clarified experimentally for the first time. Although theoretical calculations has predicted MgB₄ to be a semiconductor, the electron energy-loss spectrum in this study show a plasmon peak at 0.4 eV, which might be due to carrier electrons. Theoretical calculations suggested that the electronic states near the Fermi energy are localized along the one dimensional B₆ cluster chain. Therefore, one–dimensional electric conductivity is expected.