title: Resonant X-ray emission with a standing wave excitation.
abstract: The Borrmann effect is the anomalous transmission of x-rays in perfect crystals under diffraction conditions. It arises from the interference of the incident and diffracted waves, which creates a standing wave with nodes at strongly absorbing atoms. Dipolar absorption of x-rays is thus diminished, which makes the crystal nearly transparent for certain x-ray wave vectors. Indeed, a relative enhancement of electric quadrupole absorption via the Borrmann effect has been demonstrated recently. Here we show that the Borrmann effect has a significantly larger impact on resonant x-ray emission than is observable in x-ray absorption. Emission from a dipole forbidden intermediate state may even dominate the corresponding x-ray spectra. Our work extends the domain of x-ray standing wave methods to resonant x-ray emission spectroscopy and provides means for novel spectroscopic experiments in d- and f-electron systems.
authors.affiliation: Department of Physics, University of Helsinki, P. O. Box 64, FI-00014, Finland.
authors.forename: Kari O
authors.initials: KO
authors.lastname: Ruotsalainen
authors.affiliation: Department of Physics, University of Helsinki, P. O. Box 64, FI-00014, Finland.
authors.forename: Ari-Pekka
authors.initials: AP
authors.lastname: Honkanen
authors.affiliation: Diamond Light Source, Didcot, Oxfordshire, OX11 0DE, UK.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Collins
authors.affiliation: Physics Department, University of Trento, Via Sommarive 14, 38123 Povo (TN), Italy.
authors.forename: Giulio
authors.initials: G
authors.lastname: Monaco
authors.affiliation: ESRF - The European Synchrotron, CS40220, 38043 Grenoble Cedex 9, France.
authors.forename: Marco
authors.initials: M
authors.lastname: Moretti Sala
authors.affiliation: ESRF - The European Synchrotron, CS40220, 38043 Grenoble Cedex 9, France.
authors.forename: Michael
authors.initials: M
authors.lastname: Krisch
authors.affiliation: Department of Physics, University of Helsinki, P. O. Box 64, FI-00014, Finland.
authors.forename: Keijo
authors.initials: K
authors.lastname: Hämäläinen
authors.affiliation: Department of Physics, University of Helsinki, P. O. Box 64, FI-00014, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Hakala
authors.affiliation: Department of Physics, University of Helsinki, P. O. Box 64, FI-00014, Finland.
authors.forename: Simo
authors.initials: S
authors.lastname: Huotari