Transcript Intermediate Valence in Yb Compounds Probed by RIXS and 4f

8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
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Intermediate Valence in Yb Compounds
Probed by RIXS and 4f Photoemission
Serguei L. Molodtsov,
European XFEL & Freiberg University of Technology
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Cooperators
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Studies were performed by:
Dresden University:
K. Kummer (ESRF), D. Vyalikh,
Yu. Kucherenko, S. Danzenbächer,
M. Holder, C. Laubschat
ESRF (ID16):
S. Huotari and L. Simonelli
Spring-8 (BL25SU):
T. Muro, Y. Kato and T. Kinoshita
MPI CPfS Dresden:
C. Krellner and C. Geibel
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Correlated f-materials
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Periodic table
Electron configuration:
of the elements
n
m
2
[Xe] 4f 5d 6s
Atomic
potential
Lanthanoide
:
f - electrons
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Correlated f-materials: YbRh2Si2
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Correlated f-Materials
Periodic table
of the elements
Lanthanoide
:
f - electrons
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Correlated f-materials: Mixed-valent Ce and Yb systems
E
DOS
E
f
EF
d
f
EF
d
ef1
e f0
DOS
f electron promotion
energy Ufd may
be compensated by
increase of the system
cohesive energy DUC
Ufd >> DUC – stable configuration fn [f1 for Ce; f14 (h0) for Yb]
Ufd << D UC – stable configuration fn-1 [f0 for Ce, f13 (h1) for Yb]
Ufd ~ DUC – mixed-valent system fv, (n-1) < v < n
S.L. Molodtsov, European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
From mixed-valent to Kondo behavior (Ce)
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Why exact knowledge of intermediate
valency is important ?
E
ef2
Mixed valence:
Uff
f states
ef1 and ef0 are almost equally
possible
efficient hopping
short lifetime
Kondo ef0
EF
ef
1
broad EF peak
Kondo:
Ufd
starting from ef1, probability
to have
e f0
is very low
hopping is rear
long lifetime
sharp Kondo resonance
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Intermediete valency from photoemission
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Ce:
εf = -1.5 eV
Δ = 1.0 eV
Yb:
εf = -0.05 eV
Δ = 0.3 eV
SIAM
calculations
Uff = 7 eV
J.-M. Imer & E. Wuilloud,
Z. Phys. B 66, 153 (1987).
GSP breaks down, since it underestimates experimental intensity
at EF. Final-state hybridization should be included in consideration!
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Final-state hybridization is included!
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Ce:
εf = -1.5 eV
Δ = 1.0 eV
SIAM
calculations
Yb:
εf = -0.05 eV
Δ = 0.3 eV
Uff = 7 eV
O. Gunnarsson &
K. Schönhammer,
PRB 31, 4815 (1985)
In case final state hybridization and finite valence-band width are considered
better agreement between theory and experiments can be achieved
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Intermediete valency of YbRh2Si2 from photoemission
Divalent (2+) contribution into the ground
state is considerably overestimated in
photoemission experiments
S.L. Molodtsov, European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
RIXS at L3 edge
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2p54f14 configuration energetically preferred due to its better core-hole screening. Because of
possible d→f electron hopping, the 2+ line thus might enter overemphasized into the spectra
Constant emission energy (CEE)
and constant excited energy (CXE)
spectra can be calculated
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Intermediarte valency from RIXS
CXE at excitation energy of 2+ resonance is
preferable for analysis of almost 3+ system
with ζ = 1 for CEE scan and ζ < 1 for CXE scan
S.L. Molodtsov, European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Intermetallic rare-earth materials: YbRh2Si2
Typical single-crystalline samples
S.L. Molodtsov, European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Intermetallic rare-earth materials: YbRh2Si2
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Yb
Rh
Si
Quasi-layered structure, cleave between Yb (blue) and Si (green) layers
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Characterization of cleaved samples: YbRh2Si2
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Yb
Rh
Si
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Characterization of cleaved samples: YbRh2Si2
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Surface
Yb
Rh
Si
Bulk
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Evaluation of photoemission spectra
Best fit for Δ = 0.26 eV
S.L. Molodtsov, European XFEL & TU Freiberg
Intermediate valency 2.93 for bulk is observed
(2.88 in GSP)
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Evaluation of RIXS spectra
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Intensity map of the Yb Lα1 fluorescence yield for YbRh2Si2
CEE and CXE cuts through the 2+ resonance are indicated by white and red circles, respectively
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
CEE cut through the intensity map
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XAS measured in total
fluorescence yield (TFY)
mode and RIXS spectra in
CEE mode of YbRh2Si2
Spectral broadening is no
longer defined by the lifetime
of the deep 2p core hole
(TFY-XAS), but by the much
shallower 3d core hole (CEE)
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
CXE cut through the intensity map
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Emission intensity curve
along the CXE cut (excitation
into 2+ resonance) indicated
by red circles in fig. below
Originally small 2+ intensity is
now comparable to that of the
3+ resonance, despite the only
small 2+ divalent admixture in
the ground state.
But, further normalization is required!
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Absolute intensity normalization
ζ = 0.13
Information on the absolute intensity ratio between the 2+ and 3+ peaks
in their respective resonance maxima can be obtained comparing CEE
and CXE cuts crossing maximum of the 2+ signal in the intensity map
S.L. Molodtsov, European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Evaluation of RIXS spectra
Δ = 0.26 eV
from photoemission
Intermediate valency: 2.93 from CEE scan and 2.92 from CEE scan
(2.89 and 2.88 in GSP)
S.L. Molodtsov, European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Summary
Valency 2.95 is inferred from low-excitation measurements of the
Kondo temperature (20 K)
Both RIXS and photoemission approaches to determine
valency fail if only initial-state properties are accounted for
(2+ contribution is overestimated)
Consideration of final-state hybridization is necessary to
obtain correct valency
S.L. Molodtsov, European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
European XFEL (XFEL.EU)
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Superconducting LINAC technology
provides 27.000 light pulses/s with
duration down to a few fs each. It
makes XFEL.EU attractive for photonhungry and time-resolved experiments.
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Heisenberg RIXS (hRIXS) @ XFEL.EU
Spokesperson: Alexander Föhlisch, HelmholtzZentrum-Berlin, Potsdam University, Germany
Consortium members: Cooperation of
representatives of 20 distinguished research
institutions from
7 European countries:
Germany, Italy, Switzerland,
Sweden, the Netherlands,
Finland and France
S.L. Molodtsov, European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Experimental hall
S.L. Molodtsov, European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Soft X-ray hall (SASE3): Floor plan
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42.5 m
15.5 m
S.L. Molodtsov, European XFEL & TU Freiberg
8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Completion of underground construction (06.06.13)
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Tunnels: Infrastructure installation
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
European XFEL: Campus
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Main building: Architect’s view
S.L. Molodtsov, European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
Main building: Architect’s view
S.L. Molodtsov,
European XFEL & TU Freiberg
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8th International Conference on Inelastic X-Ray Scattering IXS-2013, May 12-15, Menlo Park
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You are very welcome
to plan your IXS/RIXS experiments
at the European XFEL
S.L. Molodtsov, European XFEL & TU Freiberg