X-Ray Absorption Spectroscopy
description
Transcript of X-Ray Absorption Spectroscopy
MAX-PLANCK-UBC CENTRE FOR
QUANTUM MATERIALS
International Summer School on Surfaces
and Interfaces in Correlated Oxides
30th
August, 2011
Dipartimento di Fisica
Politecnico di Milano
Italy
Giacomo Ghiringhelli
Giacomo Ghiringhelli
Introducing myself...
2
Picture of POLIMI
Keywords:
• Synchrotron radiation
• Soft x-rays
• Resonant spectroscopy
• 3d transition metal oxides
Giacomo Ghiringhelli
Summary
3
1. Why synchrotron radiation?
• Main properties
• Absorption edges and x-ray energies
2. XAS: x-ray absorption spectroscopy
• Basic process and the choice of absorption edges
• XLD and XMCD: polarization dependent XAS
• Some examples on oxide interfaces
3. RIXS: resonant inelastic x-,ray scattering
• A second order process
• dd excitations
• Magnetic excitations
Giacomo Ghiringhelli
Synchrotron radiation, summary
4
Giacomo Ghiringhelli
Undulators: many photons
5
Giacomo Ghiringhelli
Undulators: polarization control
6
L u c e p o l a r i z z a t al i n e a r m e n t e
L u c e p o l a r i z z a t ac i r c o l a r m e n t e
E l e t t r o n i
E l e t t r o n i
C a m p o m a g n e t i c o
C a m p o m a g n e t i c o
Full control of the polarization at the source:
• Linear horizontal or vertical or any orientation (more difficult)
• Circular Right or Left handed
Giacomo Ghiringhelli
Beam line
7
High quality mirrors, gratings and crystals are needed to make the beam monochromatic (bandas narrow as possible)and to focalize it onto the sample
Parameter Typical figures
Flux at the sample 1010 - 1013 photons/s
Beam size at sample (hoz x ver) 50 m x 5 m - 1 mm x 1 mm
Energy bandpass: UV (20 – 50 eV)soft x rays (300 – 1000 eV)hard x rays (2 - 10 keV)
10 - 50 meV50 – 500 meV50 – 500 meV
State of the art beam lines for resonant spectroscopy
Giacomo Ghiringhelli
X-ray spectroscopy for 3d Transition Metal systems
8
X-ray resonant spectroscopies
• XAS: x-ray absorption
spectroscopy
• XLD and XMCD: polarization
dependent XAS
• RIXS: resonant inelastic x-ray
scattering
• Resonant reflectivity
• Resonant Elastic X-ray
Scattering
• Resonant Photoemission
E
EF
Ev
3dTM oxides
3p
2p
1s
4sp3d
Ox 2p
Giacomo Ghiringhelli
X-ray Absorption measurements
9
X rays
e
X rays
nA
Tunable or “white” source
Monochromator
Detection:
• transmission (only hard x-rays)
• fluorescence yield
• electron yield (including drain current)
Giacomo Ghiringhelli
X-ray Absorption Cross Section
10
0.0
0.5
1.0
1.5
2.0
2.5
10 100 1000 10000
1E-4
1E-3
0.01
0.1
1
Cu K
9000 eV
O K
530 eV
A
bso
rpti
on
co
eff
icie
nt
(arb
. u
.)
Photon Energy (eV)
CuOCu L
2,3
930-950 eV
log scale
Linear
scale
Cu
M edges
Giacomo Ghiringhelli
Resonances in the XAS
11
K edge 530 eV
3d
EFermi
E
3p
2p
1s
1s
2sM2,3 edges (28-77 eV)
L2,3 edges (400-950 eV)
K edge (4.5-9.0 keV)
2p
3d TM Oxygen4sp
2p
Rare Earths
L2,3 edges
(5.5-10 keV)
3dM4,5 edges
(830-1580 eV)
6s,5d
4f
Strong resonances
Giacomo Ghiringhelli
Core levels
12
0 10 20 30 40 50 60 70 80 90 100
10
100
1000
10000
100000
O
GG - Politecnico di Milano; Source: X-ray data booklet, Lawrence Berkeley National Laboratory 25/03/02 18:29:59
4d5/2
4p3/23d
5/23p
3/2
2p3/21s
Fe Mo Th
Actinides
AuLuGdCe
RE
CdYZnSc
4dTM3dTM
SiC
Hard
X-R
ay
sS
oft
X-R
ay
sU
V
Bin
din
g e
ner
gy
(eV
)
Atomic number Z
K
L3
M3
M5
Giacomo Ghiringhelli
3p: M2,3 edge XAS
13
Source: S. Nakai, et al PRB 9, 1870 (1974)
Spin-Orbitsplitting
Spin-Orbitsplitting
Giacomo Ghiringhelli
2p: L2,3 edge XAS
14
640 645 650 655 660
MnO
photon energy (eV)
Mn L2,3
XAS
La0.7
Sr0.3
MnO3
Spin-Orbitsplitting
Source: G. Ghiringhelli, N.B. Brookes et al unpublished Source: C. Aruta, G. Ghiringhelli et al unpublished
850 860 870 880
850 855 860
L2
Photon Energy (eV)
Ni metal
NiO
L3 L
3
Ni metal
NiO
Spin-Orbitsplitting
Giacomo Ghiringhelli
Atomic model
15
Total E3dTM - O
|g>
2p53dn+2L
2p53dn+1
3dn
3dn+1L
C.I. M.S.
M.S.: Multiplet
Splitting
C.I.: Configuration
Interaction
XAS probes
orbital occupation
Giacomo Ghiringhelli
L3 XAS and multiplets
16
Ground state
EExcitation
Resonant scattering without relaxation of intermediate state
Ground
state
Intermediate
states
Final states
Time
De- excitations
hin
h
e
out
out
2p3/2
3d
3d n 2p53d n+1
Excited states
NiO: 3d8 3d9
MnO: 3d5 3d6 Many peaks
636 638 640 642 644 646
photon energy (eV)
MnO
CuO: 3d9 3d10 One single peak
928 930 932 934
Photon Energy (eV)
CuO
Giacomo Ghiringhelli
L3 XAS and valence
17
Cu metal: 3d104s1
L3
L2
Cu2O: Cu1+ is 3d10
CuO: Cu2+ is 3d9
Source: M. Grioni et al PRB 45, 3309 (1992)
930 935 940
Photon Energy (eV)
CuO
Cu2O
2.1 eV
Source: M. Finazzi et al PRB 61, 4629 (2000)
Giacomo Ghiringhelli
X-ray absorption intensity
18
Fermi golden rule
Matrix elementJoint density of states, separatedby energy h
Electric dipole perturbation associated to a photon
Giacomo Ghiringhelli
Electric dipole selection rules
19
0
13
4Yruε
Radial integral
dYYdrRRr irfifif uεrε**3
Angular integral
Selection rules(via Wigner- Eckart)
Mind the nodes of R!NB what matters is Rf ,in the presence of the core hole!
mpm YYY 11
'*
2
Transitions pd
m=-1,0,+1p=-1,0,+1m’=m-1,m,m+1
l=1
l=0
l=2
Giacomo Ghiringhelli
Crystal field
20
Cubic
Oh
10Dq
eg
t2g
d states
xy, yz,zx
x2-y2, z2
Spherical
O3
10Dq
eg
b2yz,zx
x2-y2
z2
xy
a1
b1
Tetragonal
D4h
x
y
z Cu: x -y orbital2 2
Giacomo Ghiringhelli
3d split states
21
xy
z
x
y
z
xy
z
xy
z
x
y
z
x2-y2z2
xy
yz
zx
b1 a1
b2
e
eeg states
t2g states
Spherical harmonics and orbitals
22
|Y1-1|2 = |Y11|
2 |Y10|2
Y1-1=
Y11=
Y10=
2p
stat
es a
ll o
ccu
pie
d:
sph
eric
al d
istr
ibu
tio
n
3d
stat
es p
artl
y em
pty
:an
iso
tro
py
in f
inal
sta
tes
|Y2-2|2 = |Y22|
2 |Y2-1|2 = |Y22|
2 |Y20|2
Giacomo Ghiringhelli
2p to 3d transitions
23
• Spherical distribution
• No well defined spin state
• Spin “parallel” to orbital moment
2p3/23d
• Anisotropic occupation due to crystal field
• Possible spin polarization (FM or AF)
• Spin-orbit interaction not always negligible
photon
RCP = Y11
LCP = Y1-1
z-linear = Y10
x-linear = (Y1-1+Y11)/sqrt(2)
Giacomo Ghiringhelli
Transition of a hole from 3d to 2p
24
2p3/23d photon
Example: transition to a 3d(x2-y2) orbital
RCP = Y11
Final state 2p hole has main spin up character
Initial state 3d hole is100% spin down
Giacomo Ghiringhelli
Linear polarization of x-rays: orbital occupation
25
x
y
z
x2-y2b1
E
h in
Empty 3d state
E
High absorption
No absorption
(Y1-1+Y11)
(Y2-2+Y22)
Y10
xy
z
z2a1
E
h in
E
Weak absorption
High absorption
Empty 3d state
Y20
Giacomo Ghiringhelli
3d hole symmetry in cuprates
26
h E
Result: the hole in Cu2+ has 100% x2-y2 symmetry
3d9 (2p3/2)33d10
Giacomo Ghiringhelli
Linear polarization of x-rays: magnetization orientation
27
E
h in
Atomic spin orientation
E
Different absorption
E
h in
E
M
Atomic spin orientation
M
Same absorption
MAGNETIC LINEAR
DICHROISM:
Works for Ferro and AntiFerro
Giacomo Ghiringhelli
Circular polarization of x-rays and ferromagnetic materials
28
m=-1
z
RCP
m=1z
LCP
MXAS-MCD
experimental geometry
sample
E
Fermi level
3d
2pj=3/2
j=1/2
z
M
LCP
RCP
m
XAS-MCD: x-ray absorption magnetic circular dichroism
number offree states
matrixelements
transitionrates
absorption
LCP RCP
3d
2p3/2
L3
M
L3: 2p3/2 3d
L2: 2p1/2 3d
Giacomo Ghiringhelli
XMCD: sum rules
29
700 720 740 760 780 800 820 840 860 880 900-2
-1
0
1
2
3
4
5
6
7
8
In
tensi
ty (
arb. unit
s)
Photon energy (eV)
-10
0
10
20
30
40
L2
L3
L2
L3
Inte
gra
ted I
nte
nsi
ty (
arb. unit
s)
L2
L3
Fe
(L3+L
2)
(L3)
(L3+L
2) Co
(L3+L
2)
(L3)
(L3+L
2)
Ni
(L3) (L
3+L
2)
(L3+L
2)
For late 3dTM sum rules allow to extract spin and orbital magnetic moments
directly from spectra without the need of theoretical simulations of spectra
Giacomo Ghiringhelli
XAS: some examples
30
Manganite thin films
• Strain and orbital occupation
• Magnetic anisotropy (FM and AF)
STO/LAO interface
Cuprates: ferromagnetism
Giacomo Ghiringhelli
Films of La2/3Sr1/3MnO3: strain and phase separation
31
Manganites:
→ Mn3+/Mn4+
→ CMR
→ Phase separation
→ Orbital ordering
Mn3+: 3d4
Mn4+: 3d3
LaMnO3 Mott Hubbard Insulator:Mn – Mn fluctuations more likely than O - Mn
Giacomo Ghiringhelli
Manganites XAS: strain and orbital occupation
32
637 644 651 658
-0.6
-0.3
0.0
0.3
0
2
4
6
8
V-H
[a.u
.]
Photon Energy [eV]
V (E//ab)
H (E//c)
100 u.c.
XA
S (
V, H
) [a
.u.]
Linear Dichroism=IXAS//ab-IXAS//c
z-in
xzyz
eg
t2gxyxzyz
z2
x2-y2
xy
Doct
x2- y2 z2
Preferential occupation of in-plane 3dx2-y2 orbitals
637 644 651 658
-0.6
-0.3
0.0
0.3
0
2
4
6
8
V-H
[a.u
.]
Photon Energy [eV]
V (E//ab)
H (E//c)100 u.c.
XA
S (
V,
H)
[a.u
.]
xzyz
eg
t2g
x2- y2 z2
xyxzyz
x2- y2
z2
xyDoct
z-out
Preferential occupation of the out-of-plane 3dz2–r2 orbitals
LaAlO3 substrate
LAO
LSMO
c/a=1.04
SrTiO3 substrate
STO
LSMO
c/a=0.98
Giacomo Ghiringhelli
Manganites XAS: strain and dimensionality
33
How strain and reduced dimensionality influence magnetic and orbital anisotropies
Giacomo Ghiringhelli34
Manganites XAS: ferromagnetic behavior
XMCD: FM hysteresis loops
Giacomo Ghiringhelli
Manganites XAS: linear dichroism
35
LD: magnetic and orbital anisotropy
Giacomo Ghiringhelli
Manganites XAS: magnetic linear dichroism
36
MLD: ferromagnetic and antiferromagnetic anisotropy
Giacomo Ghiringhelli
Manganite superlattices
37
Koida et al, PRB 66 144418 (2002)
Bhattacharya et al, PRL 100 257003 (2008)
(SrMnO3)n/(LaMnO3)2n
LaMnO3 : Mott insulator, Mn3+, 3d4, AFM
SrMnO3 : band insulator, Mn4+, 3d3, AFM
Giacomo Ghiringhelli
Manganite superlattices: the effect of layer thickness
38
SrO
MnO2
MnO2
LaO
MnO2
LaO
MnO2
SrLa
OMn
n = 1, 5, 8
SMO film
LMO film
C. Adamo et al, App. Phys. Lett. 92, 112508 (2008)
Giacomo Ghiringhelli
LMO/SMO: linear dichroism
39
XLD at room T, no magnetic order, the dichroism isgiven only by the orbital occupation
C. Aruta, C. Adamo, A. Galdi, P. Orgiani, V. Bisogni, N. B. Brookes, J. C. Cezar, P. Thakur, C. A. Perroni, G. De Filippis, V. Cataudella, D. G. Schlom, L. Maritato, and G. Ghiringhelli, Phys. Rev. B 80, 140405(R) (2009),
Giacomo Ghiringhelli
LMO/SMO: linear dichroism
40
XLD at low T,magnetic+orbital signal, we take outthe room T XLD to remain with the magnetic dichroism only
C. Aruta, C. Adamo, A. Galdi, P. Orgiani, V. Bisogni, N. B. Brookes, J. C. Cezar, P. Thakur, C. A. Perroni, G. De Filippis, V. Cataudella, D. G. Schlom, L. Maritato, and G. Ghiringhelli, Phys. Rev. B 80, 140405(R) (2009),
Giacomo Ghiringhelli
LMO/SMO: linear dichroism
41
What do we learn about magnetic (AFM+FM) ordering?
C. Aruta, C. Adamo, A. Galdi, P. Orgiani, V. Bisogni, N. B. Brookes, J. C. Cezar, P. Thakur, C. A. Perroni, G. De Filippis, V. Cataudella, D. G. Schlom, L. Maritato, and G. Ghiringhelli, Phys. Rev. B 80, 140405(R) (2009),
Giacomo Ghiringhelli
LAO/STO XAS: measurements and and Ti4+ calc.
42
Looking for Ti3+ signal at the interface:
→ Ti4+ is 3d0
→ Ti3+ is 3d1 (like in LaTiO3)
Ti L2,3 XAS can be perfectly simulated in single ion model(just play with Slater integrals and lifetime broadening)
Giacomo Ghiringhelli
LAO/STO XAS: linear dichroism
43
Linear Dichroism:
LD = Iz - Ix = Ic – Iab = IH-IV
Remember : (001) surface
M. Salluzzo, J. C. Cezar, N. B. Brookes, V. Bisogni, G. M. De Luca, C. Richter, S. Thiel, J. Mannhart, M. Huijben, A. Brinkman, G. Rijnders, and G. Ghiringhelli, Phys. Rev. Lett. 102, 166804 (2009),
Giacomo Ghiringhelli
LAO/STO: anisotropy of empty 3d orbitals
44
→NO detectable 3d1 signal!
→In plane orbitals ar pulled down towards EF
Vacuum Interf. Bulk LAO Interf.
Giacomo Ghiringhelli
Interface of STO with other materials
45
458 460 462 464 466 468
-0.08
-0.04
0.00
0.04
0.08
LD
no
rm (
arb
.u.)
Photon energy (eV)
LAO
LGO
NGO
LD
The trend confirms the role of the apical oxygen at interface: LD is stronger when the overlayer has smaller lattice parameter
C. Aruta et al, unpublished
XMCD
When coupled to manganitesa 3d1 contribution appearswith ferromagnetism, revealed by XMCD
F.Y. Bruno, et al. Phys. Rev. Lett. 106 147205 (2011)
Giacomo Ghiringhelli
Ferromagnetic signal in cuprates
46
La2/3Ca1/3MnO3
YBa2Cu3O7
superlattice
Giacomo Ghiringhelli
Cuprates: weak ferromagnetism
47
Giacomo Ghiringhelli
Cuprates XMCD: not only a question of interface
48
Benfatto et al. PRB 74 024416 (2006)
Djaloszinsky-Moriya interaction at the origin of weak ferromagnetismin AF undoped compounds (La2CuO4). XMCD absent in Sr2CuO2Cl2.
We find XMCD in doped compounds too.
Giacomo Ghiringhelli
Cuprates XMCD: evaluating the canting angle
49
Giacomo Ghiringhelli
Second order processes
50
What about looking at the emitted x-raysafter a resonant absorption?
We can access local and collective excitations.
Electric dipole selection rules are not an obstacle.
Photon momentum can be used to probe dispersion.
h in
polarisation
x
sample y
z
h out e
spinout
Giacomo Ghiringhelli
RIXS: a resonant inelastic scattering
51
RIXS probes charge neutral local excitations
h in
|g>
|i>
|f>
h out
Etransferred=h in-h out
Charge Transfer
dd excitations3dn*
3dn+1L
Giacomo Ghiringhelli
RIXS in a metal (if it had worked...)
E
h out
EF
h in
h out -h in
J-DOS
0Eloss
The excited electron is bound:the whole process creates excitations
across the Fermi level (somehow similarly to optical
absorption).h out depends on h in.
Actually spactra a re domiated by fluorescence...
Giacomo Ghiringhelli
Resonant fluorescence, or XES
E
h out
EF
h in
h out
Projected DOS
The excited electron is “lost”:its final energy is not importantand the emission spectrum is
independent of h in.
Giacomo Ghiringhelli
RIXS works well if there is a gap
E
EF
h out -h in
Charge excit.:continuum
0Eloss
Charge neutral excit.:sharp peaks in the gap
EExcitation
Resonant scattering without relaxation of intermediate state
Ground
state
Intermediate
states
Final states
Time
De- excitations
hin
h
e
out
out
Strongly correlatedsystems usually
give nice RIXS spectra
Gapped systems:
Excitations insidethe gap
Giacomo Ghiringhelli
Low energy excitations in L2,3 edge RIXS
-7 -5 0-6 -4 -3 -2 -1 1
(C)
Relative emitted energy (eV)
Inte
nsity (
arb
. units)
excited states
Energy loss
elas
tic
Giacomo Ghiringhelli
Electronic, magnetic and vibrational excitations in RIXS
1meV 10meV 100meV 1eV 10eV
Electronic
Magnetic
Phonons
ddCT
Optical gap
What excitations can we observe by RIXS?
Giacomo Ghiringhelli
L edge RIXS : energy and momentum transfer
Resonant Inelastic X-ray Scattering:
• an energy loss experiment
• made with photons of high energy
• at a core absorption resonance
k’
k
q = k-k’
h = E - E’
Energy
Momentum
E’, ’, ’k
E, , k
Scattering plane
S amp le
Conservation laws:
• Energy
• Momentum
• “Angular momentum”
Giacomo Ghiringhelli
Photon momentum and kinematics
1m 10m 100m 1 10 100 1k 10k 100k
1E-3
0.01
0.1
1
10
k (
Ang
-1)
energy (eV)
Wavevector of particles used in inelastic scattering
Thermal
neutrons
M e
dg
es
L e
dg
es K
ed
ge
s
Neutrons
Pho
tons
1st Brillouin zone boundary
Photons vs Neutrons: energy and momentum
Giacomo Ghiringhelli
Cuprates: the “easy” case
59
In cuprates Cu is divalent: Cu2+ 3d9
This makes XAS almost trivial: 1 peak only
3d9 (2p3/2)33d10
928 930 932 934
Photon Energy (eV)
CuO
RIXS can be calculated even by hand:
3d9 (2p3/2)33d10 (3d9)*
Even for magnetic excitations (spin waves), because fast collision approximation is a very good approximation
Giacomo Ghiringhelli
CubicOh
10Dq
eg
t2gxy, yz,zx
x2-y2, z2
SphericalO3
10Dq
eg
b2yz,zx
x2-y2
z2
xy
a1
b1
TetragonalD4h
d states
Interatomic exchange
10Dq
eg
b2yz,zx
z2
xy
a1
b1
x2-y2
dd excitations in Cu2+ systems
3d9 2p53d10 3d9
Giacomo Ghiringhelli
Cu L3 edge RIXS: CuO, La2CuO4, Malachite
61
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
0
7
14
21
Inte
nsi
ty(p
h.s-1
eV
-1)
Energy loss (eV)
CuO
La2CuO
4
Cu2(OH)
2CO
3
x2Different Cu2+
coordination, symmetry,
hybridization
Different dd excitations
Cu2+ in squareapproximately
planar coordination
Cu-O distances:
CuO 1.7 – 2-2 Ang
LCO 1.9 – 2.4 Ang
Malachite 1.9 – 2.6 Ang
Giacomo Ghiringhelli
Layered cuprates
M. Moretti Sala, V. Bisogni, L. Braicovich, C. Aruta, G. Balestrino, H. Berger, N. B. Brookes, G.M. De Luca, D. Di Castro, M. Grioni, M. Guarise, P. G. Medaglia, F. Miletto Granozio, M. Minola, M. Radovic, M. Salluzzo, T. Schmitt, K.-J. Zhou, G. Ghiringhelli, New J. Phys. 13, 043026 (2011)
By using the calculated RIXS cross sections to fit the data the energy of all the 3d orbitals can be obtained from teh RIXS spectra for any compound.
Giacomo Ghiringhelli
Ni L3 edge: NiO, NiCl2
63
Ni2+ (3d8) in octahedral
coordination
-4 -3 -2 -1 00
20
40
Inte
nsi
ty(p
h.s-1
eV
-1)
Energy loss (eV)
NiO
NiCl2
a
b
c
xy
z
a b
c
x y
z
Giacomo Ghiringhelli
Ni2+ in NiO: dependence on incident photon energy
64
G. Ghiringhelli et al , Phys Rev Lett 102, 027401 (2009)
852 853 854 855 856 857 858
852 853 854 855 856 857 858
-5
-4
-3
-2
-1
0
5
4
3
2
1
0
0 25 50 75 100852 853 854 855 856 857 858
0
1
2
3
4
5 NiORIXS
Energ
ylo
ss(e
V)
Incident photon energy (eV)
S
Inte
nsi
ty(a
rb.u
.)
NiONi L
3 XAS
P
NiO
PS P
RIXS Intensity (ph. s-1
eV-1
)
Energ
ylo
ss(e
V)
NiCl2
x5
Giacomo Ghiringhelli
Many excited states
65
Crystal field model: Sugano-Tanabe diagrams
0.0
0.5
1.0
1.5
0.0
0.5
1.0
1.5
0.00.51.01.52.02.53.03.54.0
1E
g1T
2g
3T
1g
1T
1g
1T
2g
3T
1g
1A
1g
3T
2g
1E
1g
3A
2g
1G
3P
1D
relative state energy (eV)
10D
q(e
V)
3F
10D
q(e
V)
3F
1D
3P
1G
-4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
H
relative scattered photon energy (eV)
inte
nsit
y(a
rb.u
.)
F
Ni L3 RIXS
(x2-y2), (z2)
(xy), (yz), (zx)
eg
t2g
10Dq
Single ion
Octahedral C.F.
3d spin-orbit
Exchange
Single ion
Octahedral C.F.
G. Ghiringhelli et al, J. Phys. Cond. Mat. 17, 5397 (2005) S.G.Chiuzbaian, G. Ghiringhelli et al, Phys. Rev. Lett. 95, 197402 (2005)
Giacomo Ghiringhelli
Mn L3 edge: MnO, LaMnO3
66
Mn2+ and Mn3+
in octahedral
coordination
-10 -5 0
0
5
10
15
LaMnO3
Inte
nsi
ty(p
h.s-1
eV
-1)
Energy loss (eV)
MnO
x10
Mn2+: 3d5
Mn3+: 3d4
Giacomo Ghiringhelli
An application to thin film: Mn2+ in LaxMnO3
LaxMnO3-d/STO filmsx=La/Mn ratiofor x<1 becomes FM (self doping)
MnOx=0.66x=0.88x=0.98x=1.07
XAS reveals the presence of Mn2+ for x<1
RIXS shows that Mn2+ is at site A, ie, it replaces La3+
P. Orgiani, A. Galdi, C. Aruta, V. Cataudella, G. De Filippis, C.A. Perroni, V. Marigliano Ramaglia, R. Ciancio, N.B. Brookes, M. Moretti Sala, G. Ghiringhelli, and L. Maritato, Phys. Rev. B 82, 205122 (2010)
Giacomo Ghiringhelli
STO/LAO superlattice: RIXS at Ti L3
68
Giacomo Ghiringhelli
600
500
400
300
200
100
0
-8 -6 -4 -2 0
Energy loss (eV)
Sr2CuO2Cl2
Cuprates: not only dd excitations
Giacomo Ghiringhelli
(0,0) ( ,0)
( , )
RECIPROCAL SPACE
nuclear BZ
magnetic BZ
La2CuO4: 2D spin ½ Heisenberg AF insulator
CopperOxygen
DIRECT SPACE
Elementary magnetic excitations are spin waves
Giacomo Ghiringhelli
-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5
Energy loss (eV)
La2CuO4
SAXES
Swiss Light Source
Politecnico di Milano
&
Dispersing peaks: magnetic excitations
Giacomo Ghiringhelli
R. Coldea et al, Phys. Rev. Lett. 86, 5377 (2001).
La2CuO4
L. Braicovich, J. van den Brink, V. Bisogni, M. Moretti Sala, L. Ament, N.B. Brookes, G.M. de Luca, M. Salluzzo, T. Schmitt, and G. Ghiringhelli PRL 104 077002 (2010)
LCO, comparing with INS: these are magnons!
Giacomo Ghiringhelli
Sr2CuO2Cl2
M. Guarise, B. Dalla Piazza, M. Moretti Sala, G. Ghiringhelli, L. Braicovich, H. Berger, J.N. Hancock, D. van der Marel, T. Schmitt, V.N. Strocov, L.J.P. Ament, J. van den Brink, P.-H. Lin, P. Xu, H. M. Rønnow, and M. Grioni. Phys. Rev. Lett. 105, 157006 (2010)
Another example: magnons in SCOC
Giacomo Ghiringhelli
What happens in doped, SC cuprates? NdBCO
300
200
100
0
-100
-200
Inte
nsity (
a.u
.)
-0.6 -0.4 -0.2 0.0 0.2
Energy (eV)
Insulating (annealed)Superconducting: Tc= 65K
300
200
100
0
-100
-200
Inte
nsity (
a.u
.)
-0.6 -0.4 -0.2 0.0 0.2
Energy (eV)
Giacomo Ghiringhelli
YBCO and NdBCO family (Keimer, Le Tacon)
Giacomo Ghiringhelli
Theory of magnetic RIXS (1)
76
Single ion cross section Linear spin wave theory
Giacomo Ghiringhelli
Theory of magnetic RIXS (2)
77
Giacomo Ghiringhelli
CaCuO2/SrTiO3 superlattice: superconductor
78
D. Di Castro, M. Salvato, A. Tebano, D. Innocenti, P. G. Medaglia, M. Cirillo, and G. Balestrino, arXiv1107.2239v1 (2011)
Giacomo Ghiringhelli
CaCuO2/SrTiO3 superlattice: RIXS
79
M. Minola, D. Di Castro, G. Ghiringhelli, M. Moretti Sala, N. B. Brookes, P.G. Medaglia, A. Tebano, G. Balestrino and L. Braicovich, unpublished
0
20
40
60
80
100
CCO bulk
SL n=2
SL n=3
N
orm
. In
ten
sity (
arb
. u
.)
Energy Loss (eV)
3.0 2.5 2.0 1.5 1.0
0
100
200
300
400 SL n = 2
SL n = 3
bulk CCO
0 3.01.0 2.52.01.5
Energ
y (
meV
)q//
0.5
Giacomo Ghiringhelli
With high resolution L edge RIXS
We can probe orbital and magnetic excitations
In layered cuprates we can map E(q) of magnons and
we can thus complement optical spectroscopy, EELS and INS
EXPERIMENTSthe limitations are still E resolution and intensity.
Instrumentation and perspectives
AXES at the ESRF SAXES at the SLS
Giacomo Ghiringhelli
L
Same optical scheme:
• VLS spherical grating
• CCD detector
Different length
Since 1994: AXES at beam line
ID08 of the ESRF
L = 2.2 m
Design: E/ E = 2,000 at Cu L3 (930 eV)
2010: E/ E = 5,000 at Cu L3
dvanced -Ray miss ion pectroscopyE SA X
INFM
C. Dallera et al. J. Synchrotron Radiat. 3, 231 (1996)G. Ghiringhelli et al., Rev. Sci. Instrum. 69, 1610 (1998)M. Dinardo et al., Nucl, Instrum. Meth A 570, 176 (2007)
SAXES
Swiss Light Source
Politecnico di Milano
&
Since 2007: SAXES at beam line
ADRESS of the SLS
L = 5.0 m
Design: E/ E = 12,000 at Cu L3
2008: E/ E = 10,000 at Cu L3
G. Ghiringhelli, et al Rev. Sci. Instrum. 77, 113108 (2006)V. Strocov, T. Schmitt, L. Patthey et al, J. Synch. Rad., 17, 631 (2010).
From AXES (ESRF, ID08) to SAXES (SLS, ADRESS)
Giacomo Ghiringhelli
The future of RIXS instrumentation
82
E down to 30 meV at Cu L3
and 10 meV at Ti L3
10 m
ЄRIXS:The Єuropean RIXS facility (N.B Brookes)
Other high resolution RIXS projects:
• Centurion, at NSLS II (Brookhaven Nat Lab)
• Diamond (UK)
• MAX IV (Sweden)
• NSRRC (Taiwan)
• ...
Giacomo Ghiringhelli
Bibliography
83