Measuring the hole-state anisotropy inMgB2by electron energy-loss spectroscopy

Abstract

We have examined polycrystalline ${\mathrm{MgB}}_2$ by electron energy-loss spectroscopy (EELS) and density of states calculations. In particular, we have studied two different crystal orientations, [110] and [001], with respect to the incident electron beam direction, and found significant changes in the near-edge fine structure of the B K-edge. Density-functional theory suggests that the pre-peak of the B K-edge core loss is composed of a mixture of $p_{\mathrm{xy}}$- and $p_z$-hole states and we will show that these contributions can be distinguished only with an experimental energy resolution better than 0.5 eV. For conventional transmission electron microscope/scanning transmission electron microscope instruments with an energy resolution of ∼1.0 eV the pre-peak still contains valuable information about the local charge-carrier concentration that can be probed by core-loss EELS. By considering the scattering momentum transfer for different crystal orientations, it is possible to analytically separate $p_{\mathrm{xy}}$ and $p_z$ components from the experimental spectra. With careful experiments and analysis, EELS can be a unique tool measuring the superconducting properties of ${\mathrm{MgB}}_2,$ doped with various elements for improved transport properties on a subnanometer scale.