HAXPES on 4f and 5f Strongly Correlated Systems
Work funded by the U.S. Department of Energy, Office of Science,Los Alamos National Laboratory LDRD program, and
Campaign II, MTE 2.1
HAXPES 2009 – Brookhaven National Laboratory May 20-22, 2009
John JoyceCondensed Matter and Thermal Physics Group (MPA-10)
Los Alamos National Laboratory
Volumes, Localization & Total Energy
f-electrons on the threshold of instability. Small changes in energy or temperature can change the valence or localization
-3 -2 -1 0
Binding Energy (eV)
USb2
-3 -2 -1 0
160
140
120
100
80
60
40
20
00
-20
-40
UCoGa5
Binding Energy (eV)
Localization, Itinerancy and Narrow bands
4f and 5f states span the range of localized, itinerant and the interesting middle ground of narrow bands.
Yb metalthin film
-3 -2 -1 00
Binding Energy
Single Crystal Spectroscopy
HAXPES can deliver on the promise of PES from air-prepared samples (in some cases). But we still need single crystals for intrinsic properties.
(Yb data, J.J. Joyce & C.G. Olson; UPt3 data, A.J. Arko & J.J. Joyce; U metal data, S.L. Molodtsov et. al, Phys. Rev. B 57, 13241 (1998).
-2 -1.5 -1 -0.5 0
UPt3Single X-talPoly X-tal
Binding Energy (eV)
hν =60 eV∆E~70 meV
51 52 53 54 55Kinetic Energy (eV)
Yb Film20 K evap
Yb Film200 K evap
hν =60 eV∆E~70 meV
-6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0Binding Energy (eV)
UBe13
UPd2Al3
UPt3
URu2Si2
USb2
Single Crystalhν ~ 108 eVT ~ 20 K
Strongly Correlated Uranium Materials
Sharp peak at the Fermi level is a characteristic feature of strongly correlated materials (magnetic or enhanced mass). Left: 5 strongly correlated uranium compounds with a sharp peak at the Fermi level.
USb2 ARPES – Linewidths & Dispersion
-6 -5 -4 -3 -2 -1 0
-1.5 -1.2 -0.9 -0.6 -0.3 0Binding Energy (eV)
USb2±1º
hν=110 eVhν=30 eVT~ 20 K
Left: RESPES and ARPES which has better energy and angular resolution (also probably lifetime effects). Above : ARPES at the gamma point for 34 eV.
HAXPES adds core levels for screening, MFP, higher RESPES
USb2 HAXPES and VUV
USb2 data at 22 eV and 7600 eV. The valence bands are consistent with one another. One can get reliable electronic properties information from the most surface sensitive photon energies, but HAXPES widens the range of acceptable practices.
Surfaces Can Still Matter in HAXPES
The U 4f levels for USb2, UPd3 and UGe2hν ~7.6 KeV 4f BE ~377 eV
USb2 cleaved in air and cleaved in vacuum differencesNot a deal breaker, but need to know about it
Surfaces Can Still Matter II
The Sb 3d levels for USb2, and the U 4f with O 1s for UGe2
hν ~7.6 KeV
Note - resolution matters for the cores as well as the VB
5f Electron 3d and 4d Cores
The U 3d and 4d core levels for USb2, UPd3 and UGe2hν ~7.6 KeV – 4d BE ~750 eV, - 3d BE ~ 3500 eV
2 components to each SOS level except UPd3
Transuranic XPS on PuSb2 and PuCoGa5
The Pu 4f core-levels for PuSb2 binding energy ~ 430 eV at photon energies of 1500 and 3000 eV. and PuCoGa5 at 1500 eV.
477 481 485 489 493 497
dataBKGfitDivalent bulkdivalent Surface
YbInCu4T~18 K
hv=500 eV(Hermon & Scienta)
Kinetic Energy (eV)
nf ~ 0.6
In 4d cores Yb+3Cu 3d
Yb+2
YbInCu4 Divalent and Trivalent f-electrons
The valence band and shallow
cores for YbInCu4. The In 4d levels
are typical shallow cores with a
filled shell initial state and a well
defined SOS pair in the final state.
The Cu 3d levels are band states
that show dispersion in reciprocal
space. The trivalent Yb 4f levels
arise from an atomic-like 4f13
initial state going to a 4f12 final
state.
Yb Occupancy, Valence Cross-sections
YbInCu 4hv = 90 eV
Divalent Yb 4f
Kinetic Energy (eV)
73 75 77 79 81 83 85
-2 -1.5 -1 -0.5 0
Divalent Yb 4f
Bulk Yb 4f7/2Bulk Yb 4f5/2
SurfaceYb 4f7/2
Trivalent Yb 4f
Cu 3d
484 486 488 490 492 494 496
YbInCu 4hv = 500 eV
The relative and absolute cross sections for Yb 4f levels change as well as the MFP.
5.95 KeV PES
Valence for YbInCu4 is constant from 90 to 5950 eV discounting a subsurface region.
YbAl3 -- XPS -- n f~0.6
TriValent Yb 4f
DiValent Yb 4f
-12 -10 -8 -6 -4 -2 0
YbAl3 -- UPS -- n f~0.63
Binding Energy (eV)
YbAl3 Photon Energy Dependence
For the heavy fermion YbAl3 we see a consistent picture of the valence between 100 and 6000 eV. High quality single crystal are important for consistent results. Non 4f contributions are minimized in YbAl3.
Yb Temperature, VB and 3d HAXPES
Valence band T-dep for 3 Yb materials with Yb 3d levels and reduction approach.
Yb Valence from HAXPES and RIXS
The temperature dependence and valence of the 3 Yb heavy fermions. The measured valence changes systematically depending on the binding energy of the probed energy level. The overall trends with T are consistent between different binding energies.
Summary – 4f & 5f Materials
HAXPES deliver on the versatility for samples with varied preparation but
one needs to be on guard. Contamination can be observable at 7.6 KeV.
Good agreement for U and Yb materials between low and high energy
with good samples and consistent experimental technique.
Early work on Pu materials indicates a single screening channel for PuSb2
and PuCoGa5 , USb2 shows 2 U 4f screening channels.
Determining the true valence in 4f and 5f systems continues to be a
challenging issues for strongly correlated f-electron systems.
The dependence on the f-electron occupancy with the binding energy of
the probe level remains enigmatic.
T.Durakiewicz Los Alamos National LaboratoryK. Graham Los Alamos National LaboratoryJ. Sarrao Los Alamos National LaboratoryE. Bauer Los Alamos National LaboratoryD. Moore Los Alamos National LaboratoryL. Morales Los Alamos National LaboratoryM. Butterfield Lawrence Livermore National LaboratoryE. Guziewicz Polish Academy of ScienceC. Olson (d) Ames LaboratoryH. Höchst Synchrotron Radiation Center
M. Grioni Ecole Polytechnique Fédérale (EPFL) Lausanne, SwitzerlandL. Moreschini (EPFL) Lausanne, now at U. WuerzburgC. Dallera Politecnico di Milano, p. Leonardo da Vinci Milano, ItalyV. Fritsch originally, Los Alamos National LaboratoryS. Bobev originally, Los Alamos National LaboratoryE. Carpene Politecnico di Milano, p. Leonardo da Vinci, Milano, ItalyS. Huotari European Synchrotron Radiation Facility (ESRF), Grenoble, FranceG. Vankó European Synchrotron Radiation Facility (ESRF), Grenoble, FranceG. Monaco European Synchrotron Radiation Facility (ESRF), Grenoble, FranceP. Lacovig Laboratorio TASC, INFM, Basovizza, ItalyG. Panaccione Laboratorio TASC, INFM, Basovizza, ItalyA. Fondacaro NFM and Universitá di Roma III, Roma, ItalyG. Paolicelli NFM and Universitá di Roma III, Roma, Italy P. Torelli LURE, Université de Paris–Sud, Orsay, France
HAXPES
VUV/XPS
Collaborators
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