Resonant X-Ray Diffraction in Manganites: What Can We Learn About The Coupling Between Magnetic and Orbital Order?
<-- Return to the list
Date: 12-14-2005
Start Time:
4:00pm
End Time: 11:00pm
Speaker: Jessica Thomas
From:
Brookhaven National Lab
Location: Interschool Lab, 7th floor, Schapiro/CEPSR
Hosted by:
Center for Integrated Science
Abstract:
The myriad phase transitions found in the manganites are classic examples of the effects of coupled degrees of freedom in strongly correlated materials. In this talk, I will focus on one particular phase which emphasizes this point: the orbitally and magnetically ordered ground state in insulating, half-doped manganites. "Orbital order" describes a phase transition in which the population of a particular valence electron spatial wave function on an ionic site is correlated throughout the lattice. In the case of manganites, the ionic sites of interest are the Mn ions and their strongly correlated 3d valence electrons. Since the overlap between adjacent Mn orbitals dictates their magnetic interaction, orbital ordering of the Mn sites functions as a precursor to the magnetic ground state -- or at least, this has been the picture for 50 years! The challenge to testing this picture has been the absence of a probe that can directly observe the orbital order: after all, this requires a probe which can see that the shape of the electron cloud around one Mn site is different from its neighbor's. I will explain how resonant x-ray diffraction provides such a probe and how this technique permits a unique and direct comparison of orbital and spin correlations in half-doped manganites. I will also discuss new results from coherent x-ray resonant diffraction measurements, which may be used to image the orbital order domains and probe their dynamics.