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