Regensburg 2000 – wissenschaftliches Programm
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AM: Magnetismus
AM 13: Postersitzung: Dünne Schichten (1–22), Magnetowiderstand (23–40), Phasenübergänge (41–55), Mikromagnetismus (56–68), Spektroskopie (69–77), Nanokristalline Materialien (78–82), Anisotropie (83–86), Schmelzen (87–90), Weitere Bereiche (91–100)
AM 13.72: Poster
Dienstag, 28. März 2000, 16:00–20:00, A
A sum rule for X-ray natural circular dichroism — •Robert BENOIST1 and Paolo CARRA2 — 1Institut für theoretische Physik C, Technische Hochschule Aachen, 52056 Aachen, Germany — 2European Synchrotron Radiation Facility, B.P. 220, 38043 Grenoble Cédéx, France
It is only recently that X-ray circular dichroism was observed experimentally in materials without magnetic ordering (XNCD) [1,2]. It is known to be mainly determined by the interference term between electric dipol (E1) and electric quadrupol (E2) transitions. Using Racah-algebra techniques, we derive a sum rule - similar to the sum rules for materials with a net magnetization (XMCD) [3,4] - which relates the integrated dichroic signal to the ground state of an effective operator. The latter is non-zero for systems with a helical distortion with rotation axis in the direction of the incoming photon.
[1] J. Goulon et al., J. Chem. Phys. 108, 6394 (1998).
[2] L. Alagna et al., Phys. Rev. Lett. 80, 4799 (1998).
[3] B. T. Thole et al., Phys. Rev. Lett. 68, 1943 (1992).
[4] P. Carra et al., Phys. Rev. Lett. 70, 694 (1993).