Photon Factory Activity Report 2005 #23 Part B (2006)
Electronic Structure of Condensed Matter

NE1A1/1997G288,2002G188

Anomalous Electronic Correlations in Momentum Density of Al97Li3Jadwiga KWIATKOWSKA1, Bernardo BARBIELLINI2, Stanislav KAPRZYK2,3, Arun BANSIL2,4
4Hiroshi KAWATA and Nobuhiro SHIOTANI
1H.Niewodniczanski Institute of Nuclear Physics, Krakow, 31-342, Poland
2
Northeastern University, Boston, Massachusetts 02115, USA
3
Academy of Mining and Metallurgy AGH, Krakow 30-059, Poland
4
KEK-PF, Tsukuba, Ibaraki 305-0801, JapanIntroduction
For technological and fundamental reasons theelectronic structure of Al-Li alloys has been the subject ofconsiderable attention over the years. We directly probechanges in the electronic ground state of Al due topresence of Li impurities via Compton scattering
measurements. We find that the modifications in the
momentum density of Al induced by just a few percent Li
atoms are surprisingly large and cannot be accounted forwithin the standard Fermi-liquid-type model of correlated
homogeneous electron gas.
Theoretical and Experimental Results
A single crystal of Al97Li3 was grown by the Bridgeman
method. Disc-shaped samples, 10 mm in diameter and 1.5mm thick, were cut parallel to the (100), (110), and (111)crsytallographic planes. The Compton profiles weremeasured with the high resolution Compton spectrometerat the NE1A1 beam line. The incident energy of photons
was 60 keV, the scattering angle 160 degrees, and themomentum resolution was estimated to be 0.12 a.u. The
valence electron profiles of Al for comparison weremeasured by Ohata et al.[1] under the experimental
conditions of the present measurements. Concerning thetheoretical profiles, the self-consistent electronic
structures of pure Al and the alloy were first obtainedusing the KKR-LDA-CPA scheme. Then, from that, themomentum density and Compton profiles were computed.
We consider the measured and computed changes in
the profiles due to addition of Li atoms,

differing by only about 1%. Therefore, when the
difference∆Jsph(p) is formed, we would expect suchstandard electron-gas type correlation effects to becanceled. The key to understanding this discrepancy is torecognize that correlation effects can be viewed as
exciting some electrons into higher energy unoccupied
levels as a way of modifying the character of the groundstate wave function. The lowest unoccupied orbitals in Aland Li are the 2p and the 3p orbitals, respectively. It isnatural therefore to consider the effect of promoting anelectron from an s to a p orbital. The full line in Fig. 1
represents the KKR-CPA theory corrected in a way that
3% valence electrons in Al97Li3 are promoted from s- to pstates. We may look upon the good agreement between
the corrected theory and the experiment as indicating that
correlations and the associated changes in the effective
potentials produce an enhanced p character of the groundstate wave function in Al97Li3. Given the increasing current
interest in understanding correlation effects in theinhomogeneous electron gas, our results indicate that AlLi alloys present an example of a simple binary system
which exhibits unusual correlation effects even thougheach of its two constituents is commonly thought as beinga free-electron-like metal.

∆J sph ( p )= J sph ( p ) Al − J sph ( p ) Al97 Li3Although the profiles of both Al and Al97Li3 have small
anisotropies, here we take spherical average of theprofiles because the anisotropies are smaller than thechanges we are considering and do not affect the essentialfeatures. In Fig. 1 the experimental ∆Jsph(p) is shown by
the full circles, the KKR-CPA theoretical ∆Jsph(p) isrepresented by the full squares. It is obvious that theKKR-CPA theory differs substantially from theexperiment near p=0 and 1 a.u. Deviations in theCompton profile of pure Al compared to the KKR-CPApredictions can be explained reasonably well within thestandard electron gas picture. Such standard correlation
effects are also present in Al97Li3 with a magnitude very
similar to that of Al because the electron density in Al andAl97Li3 is nearly the same with the Fermi momentum

Fig. 1 Experimental∆Jsph(p) is compared withcorresponding KKR-CPA result with and without
corrections.
References[1] T.Ohata et al., Phys. Rev. B 62, 16528 (2000).

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