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Measuring the hole-state anisotropy in MgB 2 by electron energy-loss spectroscopy

2003; American Physical Society; Volume: 67; Issue: 14 Linguagem: Inglês

10.1103/physrevb.67.144508

1095-3795

Robert F. Klie, Haibin Su, Ye Zhu, J. W. Davenport, Juan Carlos Idrobo, Nigel D. Browning, Peter D. Nellist,

Hydrogen Storage and Materials

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 \ensuremath{\sim}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.