#
# arev:/usr/local/unicat/unireq/beamreq/req00075.txt
# UNICAT Member Beam Time Request  #75

# created Fri Jul 02 16:09:20 CDT 1999
#

days:
	5

description:
	Momentum Conservation and Resonant Inelastic X-ray Scattering in 
	Al3Ni
	
	Z. Hasan and A. Panchula, Stanford University; C. Burns, Western 
	Michigan University; P. Canfield, Ames Laboratory and Iowa State 
	University; E.E. Alp, Advanced Photon Source; D. Muller and E.D. 
	Isaacs, Bell Laboratories, Lucent Technologies.
	
	Resonant inelastic x-ray scattering (RIXS) is rapidly developing as 
	a technique for probing elementary excitations in condensed matter 
	and liquid systems.   Large resonance enhancements of the inelastic 
	scattering cross-section make it possible to study electronic 
	excitations in systems where absorption would otherwise make such 
	measurements impossible.  However, the fate of resonant inelastic 
	scattering ultimately depends on whether it can be used to measure 
	the true electronic excitation spectra.  In particular, there is 
	currently heated debate as to whether resonance techniques can be 
	used to measure dispersion or rather a joint density-of-states.
	Recent studies of charge transfer excitations in insulating La2CuO4 
	have shown strong evidence that the resonant inelastic cross-section 
	has the relatively simple form; 
	 .    (1)
	
	In other words, the resonant cross-section is in fact the dynamic 
	structure factor times resonant denominators which depend on the 
	incident, wi, and scattered, wf photon energies, respectively.  This 
	form results from the fact that the excited states of the system 
	(S(q,w)) are accessed through Coulomb interactions with the 
	intermediate state (1S hole/4P electron pair).  The Coulomb 
	interaction will of course conserve energy and momentum.  The essence 
	of this study was that energy is conserved through the resonance 
	process, i.e., that excitation spectra depends only on the energy 
	difference, w = wf - wi.  However, in this study no variations with 
	q were observed for the charge transfer excitation at 6 eV.  Nor were 
	they expected since the charge transfer excitation was localized on 
	the CuO6 complex.  Therefore, there is not yet conclusive evidence the
	 resonance processes conserve momentum, q = qf - qi.
	 Therefore, we propose to study resonant inelastic scattering 
	in Al3Ni at and below the Ni K-edge.  Al3Ni is known to have a sharp 
	plasmon near 16 eV only slightly shifted from Al.  In other words, 
	Al3Ni is a free-electron like system with the added attraction of 
	having the Ni atom with an accessible K-edge at 8.333 keV.  
	Furthermore, the penetration depth in Al3Ni just below the K-edge is 
	large, ~ 50 mm.  Therefore, we should be able to measure the plasmon 
	dispersion both on-and off-resonance.  If Eq. (1) is correct these 
	two measurements will be identical, once the resonance denominators 
	are factored out.
	
	Al3Ni does not melt congruently and is thus difficult to grow in 
	large single crystals.  However, we are lucky enough to be able to 
	collaborate with Prof. Paul C. Canfield, Department of Physics and 
	Astronomy at Iowa State and Ames Laboratory who has just recently 
	grown single crystals of 1 - 2 mm in size.  Since a detailed 
	understanding of S(q,w) is essential for the success of this 
	experiment we are also collaborating with Dr. David Muller of Bell 
	Laboratories who is an expert in electron-energy-loss spectroscopy 
	(EELS).  He has already extensively studied AlNi3 and AlNi and will 
	participate in this study by measuring S(q,w) in our Al3Ni samples 
	prior to the measurement at the APS.  While we have yet to measure 
	the plasmon in Al3Ni, from Dr. Muller's previous measurements we 
	believe that the plasmon width should be about 1 eV.  This means 
	that our measurement is reasonably well matched to the ~2 eV energy 
	resolution produced by the 33ID Si(111) monochromator.  We propose to 
	work at 33ID and will provide the Si(551), spherically-bent analyzer 
	whose resolution is approximately 100 meV.  This collaboration will 
	also include Prof. Clement Burns of Western Michigan University, an 
	expert in inelastic x-ray scattering, and Zahid Hasan and Alex 
	anchula both students at Stanford University preparing theses based 
	at synchrotron facilities.
	

equipment+required:
	High resolution analyzer

experiment:
	Resonant Plasmon Dispersion

hazards:
	None

name:
	E.D.Isaacs

new+request:
	on

nonmembers:
	Several (see above)

station:
	33ID-D

unacceptable+dates:
	



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