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1 NMR1. NMR - Centro de Supercomputación de...
Transcript of 1 NMR1. NMR - Centro de Supercomputación de...
1 NMR1. NMR
2. Pnictides
J. BobroffLaboratoire de Physique des Solides, Orsay, France
CEA ( t LLB)CEA (neutrons LLB)
S h t S l ilSynchrotron Soleil
Le LPS
Université d’OrsayPolytechnique
Nuclear Magnetic ResonanceNuclear Magnetic Resonance
NMR Nobel Prices
Bloch & Purcell, Nobel Physique 1952
Zeeman, Nobel Physique 1902
Rabi, Nobel Physique 1944 Nobel Physique 1952Nobel Physique 1902 Nobel Physique 1944
Lauterbur & Mansfeld, Nobel Medecine 2003
Ernst, Nobel Chimie 1991
Wuthrich, Nobel Chimie 2002
First NMR signal in a solid and a liquid
MRI
Chemistry NMR
14 Tesla 23 Tesla
A nuclear spin I in a magnetic field H0 A nuclear spin I in a magnetic field H0
Zeeman Effect 0 0.noyauhf zH M H H I
-5/2
.
.
.5/2
-3/2-1/2o
-I E = ħ H0
resonance
1/23/2m
=I t
0= h
5/2
.
= /2 H0..
= /2 H0
How do we measure the resonance ?the resonance ?
1 put the nuclear spin 1. put the nuclear spin in a static field
2. put a transverse zoscillating field :
at the resonance, it
H0will rotate the spin
3. stop the transverse fi ld d field and measure Hoscillating
Why doing NMR ?
Zeeman : = /2 H0
in matter : = /2 Hlocal
= H0 = /2 Hloc
Difference between Hlocal and H0 : information about the viscinity of the nucleus
NMR is a local probe
because coupling between nuclear spin Iand its neighboring is very short rangeg g y g
frequency
NMR of oxygen in a cuprate
Nb of nucleiBa
H0
Y
CuO2
Y
Cu O
Local field or frequency or shift~ Hlocallocal
YBa2Cu3O7
What can you measure ?
The electron : • Orbitals• Magnetic susceptibility in different positions• Inhomogeneities
Dynamics of electrons:• correlations• Gap and symetries in superconductors• Magnetic transitions
Local fields :• magnetic ordersmagnetic orders• charge orders• vortex• spin liquids
…
The NMR shifts
Nb of nuclei 0totalK
0
total
reference0=H0
)1(,, ii
ib
zyxi KK )1(2 spinorb KK
gyromagnetic ratio depends on the nucleus
orbital or chemical shift
spin shift
Orbital Shift
used in chemistry to characterize orbitals
ligasoline
Shift orbitalShift orbital
Spin Shift Kspin
s
IHloc=H0+aH0H0
I
0
measures uniform magnetic susceptibility
AK 1
close to the nucleus
electronen
hfspin AK 2
hyperfine coupling
Kspin measures
High Tc superconductor Cuprate YBa2Cu3O6+x
KK
Alloul et al PRL (1989)
T
Alloul et al., PRL (1989)
Why not measure i tibilit i t d ?macroscopic susceptibility instead ?
Kspin measures intrinsic ff d b i inot affected by impurity
1,0
VolborthiteVolborthite
magnetic impurity
0,6
0,8
n % RMN
Squid
Volborthitespin liquid
0,4ne
shi
ft in Squid
0 0
0,2
lin
intrinsic behavior
0 50 100 150 200 250 3000,0
Temperature (K)
Mendels et al., PRL (2000)
Kspin measures at different locations of the cell
Bi2212 Oxygen NMR
at different locations of the cell
Trokiner et al., PRB (1991)
different susceptibilities pso different dopings for each planeplane
Kspin measures a histogram of , not a sum:
spin chain with non magnetic impurities
access to local variations
Ni Ni Ni Ni Ni Ni Ni Zn Ni Ni Ni Ni Ni
p g p
Y B Ni Z O
0 6
0.8
1.0 Y2 Ba Ni98% Zn2% O5 T = 200 K
s arb
itrai
res)
0.2
0.4
0.6
ensit
é (u
nité
s pur
Zn 2%
14580 14600 14620 14640 146600.0
0.2
(kHz)
Inte
Tedoldi et al., PRL 99; Das et al.PRB 04
Nb of nuclei
Zn 2%
champ local
<SZ>
Zn Ni
Alloul, Bobroff, Gabay, Hirschfeld, RMP 2009Alloul, Bobroff, Gabay, Hirschfeld, RMP 2009
Kspin measures inhomogeneities
STM
RMN
YB C O7YBaCuO
intensité
RMN
YBaCuO7YBaCuO6.6
Bi2212
0 05 0 1 0 15 0 2Cren et al., PRL 2000
P t l N t 2001 0.05 0.1 0.15 0.2dopage
JB et al., PRL 02
Pan et al., Nature 2001McElroy et al. Science 2005
dynamicsdynamics
Relaxation times in NMR
z
H T1 H0
T
T1
transverse relaxation T2 MdM
T2
transverse relaxation T2 energy is conserved YX
YXYX HMTM
dtdM
,2
,,
ZZmequilibriuZ HMT
MMdt
dM
longitudinal relaxation T1 exchange with the network Tdt 1
g
longitudinal relaxation T1
due to fluctuations of local magnetic field at RMN
1
dttiBtBT RMNLL exp)0()(~1
1
n
nt
qB
B qqAgk
TT
),()(11 "
222
1
nqBg1
examples of T1
spin-gap systemmetal Magnetic Orderspin-gap system
TAeT
1Korringa
Law
2
21
41
nBk
TKT
metal Magnetic Order
T1
1/T1
Law1 eTKT
1/T1T1/T1
TTT
TCT
BCS superconductor unconventional superconductor
T TC
1/T
gap + Hebel-Slichter Peak
1/T
power law + no Peak
1/T1 1/T1
TTC
TTC
L l fi ld i NMRLocal fields in NMR
ti d magnetic orders, charge orders,
tvortex…
Example : AF order in pnictides
Fe
Fe
Kitagawa, JPSJ 08
Effect of a charge ordersensitivity to charge through electric field gradiants (NQR)
Ch D it W i Rb M O
sensitivity to charge through electric field gradiants (NQR)
Charge Density Wave in Rb0.30MoO3
Butaud et al., PRL 1985
vortex in superconductor
champ local
YBaCuO7
L RMN d l t d L T1 i l l iti La RMN donne la carte de champs associée aux vortex
Mitrovic et al., Nature (2001)
Le T1 varie selon la position par rapport au vortex
SSummary
NMR allows to measure…
Using the spectrum position and shape: • type of orbitals (Korb)yp ( orb)• spin susceptibility at various positions (Kspin)• magnetic orderings or freezings, order parameters…g g g , p• charge orders, vortex…• inhomogeneitiesinhomogeneities
Using dynamics:Using dynamics:• dynamical susceptibilities ’’(q,)• correlations spin fluctuations• correlations, spin fluctuations• gaps, magnetic excitations• superconducting symetries and gaps• superconducting symetries and gaps
NMR study of superconductivity and magnetism in pnictidesand magnetism in pnictides
Y. Laplace, J. BobroffLaboratoire de Physique des Solides, Orsay
D. Colson, F. Rullier-Albenque, A. ForgetSPEC CEA Gif S Y ttSPEC, CEA Gif Sur Yvette
Nature of
SDW
Ba(Fe1-xCox)2As2
Nature of magnetism ?
BaSDW
SCFe
As
SC
x = dopagex(Co) %0.15
Coexistence ?
what is doping really doing ?
SDW
Ba(Fe1-xCox)2As2
SDW
SCSC
x = dopagex(Co) %0.15
Coexistence ?
An old question…
CupratesHigh Tc
d t
Organic SC Heavy fermions
« Métal »
superconductors
AF SC
doping pressure
Lefebvre 2000
Pagliuso 2001
x in CeRh1-xIrxIn5
2000 2001
YesNot yet settled,Depends on families Yesy ,rather segregated
Lee, PRL 2005
Depends on families rather nano-segregated (stripes)
Miller, PRB 2009 Lee, PRL 2005Miller, PRB 2009Sanna, PRL 2004 Mito et al., PRL 2003
A key question for the determination of the superconducting gap symmetrysuperconducting gap symmetry
PRB 2009
PRB 2009PRB 2009
PRB 2010
A true atomic coexistence is only compatible with a s+- gap symmetry
Two possible situations
T l l i S iTrue local coexistence Segregation
SupraMagnetic
SUPERCONDUCTOR
Need a local probe :RMN, SR, Mossbauer...
• SmOFeAs : segregationDrew et al, Nat. Mat. 08
• Ba1-xKxFe2As2 : segregation
,
Takeshita et al. JPSJ;Aczel et al. PRB 08; Goko PRL 08; Goko PRL 08; Fukazawa et al.,JPSJ 09;Julien et al. EuroPhys.Lett.09
Fukazawa JPSJ 09
Ba(Fe1-xCox)2As2
SDW
SC
x = dopage
Ba(Fe0.94Co0.06)2As2
0
S)c
(MK
S v
olum
ic
-1
0 10 20T (K)
Superconducting fraction : 90 - 100%
75As RMN x=6% : spectrums
400 2000
21 K
8 K 200 1000
a
b(G
)
// c (G 21 K 25 K
29 K 27 K
0 10 20 30 40 50 600 0
G)
36 K
29 K
30 K
0 10 20 30 40 50 60 T (K)
-0.05 0.00H-H0 (Tesla)
Homogeneous magnetic broadening :100% magnetic fraction below 31Kg
Coexistence in Ba(Fe0.94Co0.06)2As2
100% magneticbelow 31K200
400
1000
2000
a
b(G
)
//
below 31K
12000 0
1000
c (G
)
100% superconduct. below 21K2 600
900
NM
R cavi1 K
-1)
below 21K
Dynamically, the same Fe300
600 ity detuning1/T 1T
(s
-1
atoms display magnetismand superconductivity
0 -300
0g (kH
z)
T t i i t
0 10 20 30 40 50 60Temperature (K)
True atomic coexistence
Nature of
SDW
Ba(Fe1-xCox)2As2Nature of magnetism ?
SDW
SCSC
x = dopagex(Co) %0.15
Nature of the magnetism
undoped BaFe2As2: commensurate AF
Co6% : incommensurate AF
Kitagawa, JPSJ 08
b T=23K
H//c
Co6% : incommensurate AFand very small moment
H//ab
Incommensurability
b T 23Kb T=23K
H//c
H//ab
l,0,21 Incommensurate order
0.6
rapport calculéH//ab / H//c
0.4
H//c
ppSimulated ratio
0.2 rapport expérimentalExperimental ratio
0.00 0.25 0.50 0.75 1.00
H perp c
//ab
~ 0.04
Non doped x=0% doped x=6%No doped 0% doped 6%
TN=31KTN=135K TN 31Kmoment < 0.1 B
incommensurate SDW
TN 135Kmoment ~ 0.9 B
commensurate AF order
Incommensurability recently confirmed by neutronsconfirmed by neutrons
Pratt et al. Phys. Rev. Lett. 106, 257001 (2011)
Phase diagram from NMR/Mossbauer
moment amplitude
1 .0(NMR/Mossbauer)
AF commensurate
0 .5
.
SDW incommensurate
coexistenceincom. SDW &
0 .0
Superconductivity
0 .00 0 .05 0 .10 0 .15C o dop ingCo Doping
How can magnetism and superconductivity
A consequence of the multi(5) band character
coexist together ?
• A consequence of the multi(5)-band character of the Fermi Surface ?
M ld i i t f ti d i i t bilitM could originate from a nesting driven instabilitySC could gap different Fermi sheets
Singh & al., PRL 08
•Competition/Coexistence over different parts of the Fermi Surface seems possible even in a two band Fermi Surface seems possible even in a two band model
I thi d l i t i ibl l if th In this model, coexistence is possible only if the magnetic state is incommensurate.
--> COMPATIBLE WITH OUR MEASUREMENTS
Vorontsov & al., PRB 09
SDW
Ba(Fe1-xCox)2As2
SDW
SCSC
x = dopagex(Co) %0.15
what is doping really doing ?
160 160
100
120
140
e (K
) Ba(Fe1-xCox)2As2100
120
140
re (K
) Ba(Fe1-xRux)2As2
40
60
80
Tem
pera
ture
SDW 0.15 40
60
80
Tem
pera
tur
SDW
0 2 4 6 8 10 12 14 16 18 200
20
T
Co doping content (%)
SC0 10 20 30 40 50 60 70
0
20T
Ru doping content (%)
SC
x(Co) %Increase both the number of holes & electrons , VFermi increases, correlation
simple rigid band fillingelectron doping
decrease by a factor 3Brouet et al., 2011
p g
Co vs Ru doping
NMR shift vs substitution in the normal state :in the normal state :
0,45
0,50
0,55
0,60
B F R A d i l
Ba1-2xK2xFe2As2 : dopage en trous
0 20
0,25
0,30
0,35
0,40 Ba(Fe1-xRux)2As2 : dopage isovalent
K (%
)0 00
0,05
0,10
0,15
0,20
Ba(Fe1-xCox)2As2 : dopage en électrons
-5 0 5 10 15 20 25 30 35 40 45 50 550,00
Taux de substitution x par atome de Fe (%)
Co = electron doping Ru = chemical pressure (isovalent doping)Ru = chemical pressure (isovalent doping)
Co doping homogeneous bothfrom macroscopic and local probesp p
superconducting transition
150
T-0 5
0.0
x=6%
Susc
eptib
ility
100
TN
5 10 15 20 25-1.0
0.5
Nor
mal
ized
magnetic transition
5 10 15 20 25Temperature (K)
50 TC1.0
units
)
magnetic transition
0 2 4 6 80
Co doping x (%)0.0
0.5
MR*T
(arb
.u x=6%
Co doping x (%)0 20 40 60 80
Temperature (K)
INM
Ru doping homogeneous from macroscopic probesfrom macroscopic probes
transport & neutrons
Rullier-Albenque et al., PRB 2010 Kim et al. PRB 2011
Ru doping homogeneous from X-ray
90
0010
000
Ru sample homogeneous sample with
0070
0080
00
g sample with macroscopic segregation
000
5000
600
2000
3000
4
X-ray : 002 line
010
00
12.4 13 14 1512.4 13 14 15
Ru doping not homogeneous from NMR
But...not homogeneous from NMR
1.0 Ru 80%
Ru 50%1.0
0 6
0.8Ru 35%
Co 2%fract
ion
0 6
0.8
Co 2%fract
ion
0.4
0.6 Co 2%
mag
netic
Co 6%
0.4
0.6 Co 2%
mag
netic
Co 6%
0.2
R 15%
Ru 25%
Par
am
0.2Par
am
0 50 100 1500.0
Ru 15%
0 50 100 1500.0
Temperature (K)Temperature (K)
How to reconcile NMR inhomogeneit & NMR inhomogeneity &
macroscopic homogeneity ?
if Ru effect effect is homogeneous
100
120
140
160
e (K
) Ba(Fe1-xRux)2As2
nsit
y
40
60
80
Tem
pera
ture
SDW
NM
R In
ten
0 10 20 30 40 50 60 700
20T
Ru doping content (%)
SCTN
T
N
160
if Ru effect is averaged but on a nanoscale
100
120
140
160
ure
(K) Ba(Fe1-xRux)2As2
tens
ity
20
40
60
80
Tem
pera
tu
SC
SDW
NM
R In
t
0 10 20 30 40 50 60 700
Ru doping content (%)
SC T
Ru 20%
140
160
B (F R ) A
Ru 20%
60
80
100
120
erat
ure
(K) Ba(Fe1-xRux)2As2
0 10 20 30 40 50 60 700
20
40
60
Tem
pe
SC
SDW
0 10 20 30 40 50 60 70
Ru doping content (%)
nten
sity
T
NM
R In
T
Ru 20%Ru 20%
140
160
B (F R ) A
60
80
100
120
erat
ure
(K) Ba(Fe1-xRux)2As2
0 10 20 30 40 50 60 700
20
40
60
Tem
pe
SC
SDW
0 10 20 30 40 50 60 70
Ru doping content (%)
nten
sity
T
NM
R In
T
Ru 20%140
160
B (F R ) A
60
80
100
120
erat
ure
(K) Ba(Fe1-xRux)2As2
0 10 20 30 40 50 60 700
20
40
60
Tem
pe
SC
SDW
0 10 20 30 40 50 60 70
Ru doping content (%)
sity
NM
R In
ten
T
N
T
2*2
simulation versus experiment
0.8
1.0
Frac
tion
2*2 3*3 4*4 5*5 7*71010te
nsit
y
0.4
0.6
Mag
netic
F 1010 20*20 Infinity*Infinity expN
MR
Int
0.0
0.2
Froz
en MT
0 20 40 60 80 100
Ru substitution (%)
Local averaging of Ru effect Local averaging of Ru effect over 5*5 cell units
Reconcile macro and local
NMR start of the transition
140 Tonset seen by NMR T @ 0.5* Wipeout NMR line
the transition
100
120
K)
Tn resistivitypercolation treshold (50%)
60
80
00er
atur
e (K
resistitivity
20
40
60
Tem
pe
y
0 20 40 60 80 1000
20
Ru substitution (%)
Co doping Ru dopingsummary
Ba(Fe1-xCox)2As2
p g
RandomCo distribution :
RandomRu distribution :
l d l l Local chemical pressure Electron delocalization Local chemical pressure averaged over 1 nm
Homogeneous electronic state
Inhomogeneouselectronic state
Homogeneous low temperature low temperature phases Inhomogeneous
low temperature phases on 1 nm scale