Angle-resolved Soft X-ray Research Articles

Anisotropic electronic structure of NaAlSi studied by angle-resolved soft x-ray emission spectroscopy

The characteristic x-ray emission direction of a material indicates the direction of the bonding orbitals and spatial symmetry of the electron orbitals. Accordingly, the intensity of x-ray emission, which varies with the direction of emission and crystal orientation, provides crucial information regarding anisotropic electronic structures. This study utilized angle-resolved soft x-ray emission spectroscopy (SXES) on a layered material, NaAlSi, to ascertain the spatial distribution of the valence electrons. Distinct alterations in the spectral intensity distributions were observed in the Al–L2,3 and Si–L2,3 spectra with respect to the emission angle. To interpret the anisotropic SXES spectra, the spatial distribution of each valence electronic state was simulated using first-principle calculations. Although the anisotropic emission intensity could not explain the symmetry of the spatial distributions of the isolated s and d atomic orbitals, the anisotropy of the SXES spectra could be interpreted as the spatial distribution of these orbitals when hybridized with p orbitals. Furthermore, the spectral structure corresponding to the electronic states near the Fermi level reflected the characteristics of the d orbitals. Therefore, angle-resolved SXES measurements can effectively discern the spatial distribution of hybridized electron orbitals with specific energy levels, which could enhance techniques related to electron distribution analysis, with potential applications in material science and electronic structure characterization.

Angle-resolved soft X-ray magnetic circular dichroism in a monatomic Fe layer facing an MgO(0 0 1) tunnel barrier

The electronic and magnetic states of a monatomic Fe(0 0 1) layer directly facing an MgO(0 0 1) tunnel barrier were studied by angle-resolved X-ray magnetic circular dichroism (XMCD) at the Fe L 2,3 edges in the longitudinal (L) and transverse (T) arrangements. A strong XMCD reveals no oxidation of the 1-ML Fe, showing its crucial role in giant tunnel magnetoresistance effects in Fe/MgO/Fe magnetic tunnel junctions. Sum-rule analyses of the angle-resolved XMCD give values of a spin moment, in-plane and out-of-plane orbital and magnetic dipole moments. Argument is given on their physical implication.

Erratum: Angle-resolved soft x-ray spectroscopy study of the electronic states of single-crystalMgB2[Phys. Rev. B67, 174519 (2003)

Erratum: Angle-resolved soft x-ray spectroscopy study of the electronic states of single-crystal<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MgB</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>[Phys. Rev. B<b>67</b>, 174519 (2003)

Angle-resolved soft x-ray spectroscopy study of the electronic states of single-crystalMgB2

Angle-resolved soft x-ray measurements made at the boron K edge in single-crystal ${\mathrm{MgB}}_{2}$ provide insights into the B 2p local partial density of both unoccupied and occupied band states. The strong variation of absorption with incident angle of exciting x rays permits the clear separation of contributions from $\ensuremath{\sigma}$ states in the boron plane and $\ensuremath{\pi}$ states normal to the plane. A careful comparison with theory accurately determines the energy of selected critical k points in the conduction band. Resonant inelastic x-ray emission at an incident angle of 15\ifmmode^\circ\else\textdegree\fi{} shows a large enhancement of the emission spectra within about 0.5 eV of the Fermi level that is absent at 45\ifmmode^\circ\else\textdegree\fi{} and is much reduced at 60\ifmmode^\circ\else\textdegree\fi{}. We conclude that momentum transferred from the resonant inelastic x-ray scattering process couples empty and filled states across the Fermi level.

Angle-resolved soft X-ray emission and absorption spectroscopy of hexagonal boron nitride

Angle-resolved soft X-ray emission and absorption spectra in the BK and NK regions of hexagonal BN were measured using polarized synchrotron radiation. The take-off/incident-angle-dependence on the spectral features in both X-ray emission and absorption is clearly observed. The configuration of the σ and π orbitals, which were calculated using discrete variational (DV)-Xα molecular orbital calculations, explains the angle-resolved soft X-ray emission and absorption spectra. The relative peak intensity of the 394-eV peak in the NK X-ray emission provides useful information about the BN layer ordering.

Orbital-resolved soft x-ray spectroscopy inNaV2O5

We demonstrate that angle-resolved soft x-ray spectroscopy can resolve absorption by inequivalent oxygen sites and by different orbitals belonging to the same site in NaV2O5. By rotating the polarization direction, we see a dramatic change in the absorption spectra at the oxygen K edge. Our theory identifies the detailed composition of the spectra and predicts a correct energy-ordering of the orbitals of three inequivalent oxygen atoms. Because different orbitals dominate absorption spectra at different energies and angles, one can excite at a specific site and ``orbital''. In contrast, absorption at the vanadium L edge does not show large changes when varying the polarization direction. The reason for this is that different excitation channels (involving different initial states for the excited electron) overlap in energy and vary in compensating ways, obscuring each channel's sensitive polarization dependence.

Linear and Circular Dichroism in Angle Resolved Fe 3p Photoemission

AbstractUsing a recently developed spin-polarized, fully relativistic, multiple scattering approach based on the layer KKR Green function method, we have reproduced the Fe 3p angle-resolved soft x-ray photoemission spectra and analyzed the associated large magnetic dichroism effects for excitation with both linearly and circularly polarized light. Comparison between theory and experiment yields a spin-orbit splitting of 1.0 – 1.2 eV and an exchange splitting of 0.9 – 1.0 eV for Fe 3p. These values are 50 – 100 % larger than those hitherto obtained experimentally.