impurity effects in high tc superconductorsnano05/talks/bobroff.pdf · • impurity in more «...
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J. Bobroff, S. Ouazi, H. Alloul, P. Mendels, N. BlanchardLaboratoire de Physique des Solides, Université Paris XI, Orsay
G. Collin J.F. Marucco, V. Guillen D. ColsonLLB, CEA-Saclay LEMHE, Université Paris XI SPEC, Saclay
Impurity effects in high TC superconductors
High TC cuprates
metallicity + correlations + exotic superconductivity
doping
T
Antiferromagnetism Superconductivity
pseudogap
• Impurity in more « simple » systems• in a metal• in a BCS superconductor
• in a correlated insulator
Impurity effects in cuprates
•Impurity in High TC cuprates • in the metallic « normal » state
• macroscopic properties• local magnetism
in underdoped state with increasing doping
• in the superconducting state• macroscopic properties• density of states• magnetism
A magnetic impurity in a metal
• RKKY spin polarization of the conduction carriers
• Kondo effect
0 100 200
χ
TemperatureMadhavan et al.
CuFe AuCo
A magnetic impurity in an isotropic BCS superconductor
• Decrease of TC only if it is magnetic (Abrikosov, Gork’ov)
• Possible local bond states
dI/dV(10-7Ω-1)
NbMn or NbAg
Yazdani et al.
14580 14600 14620 14640 146600.0
0.2
0.4
0.6
0.8
1.0
ν (kHz)
Y2 Ba Ni98% Zn2% O5 T = 200 K
Inte
nsité
(uni
tés a
rbitr
aire
s)
pur
Zn 2%
An impurity in an insulating correlated system
Ni Ni Ni Ni Ni Ni Ni Zn Ni Ni Ni Ni Ni
impurity
NMR spectrum
example : Y2BaNiO5 as a spin 1 Ni chain with Haldane gap
0 2 4 6 8
-4
0
4
Zn QMC computation
δ< S
zi >/<
Sz> u
position
T=100 K
< Si.Sj > ~ e-r/ξ<SZ(i)> ~ e-r/ξ(T) / T
Das et al., 2004Tedoldi et al., 2000
Cu
J’
Zn
Cu S=1/2
J=260 K
JJ’
J’ = 0.1 à 0.2 J
An impurity in an insulating correlated system
Some other low dimension spin systems
AF orderGapξ<3
2-leg ladder
AF order
Gap
Dimerisation
Spin-Peierls Chain
No orderξ~1/TSpin ½ Chain
AF ?Gapξ < 6
Spin 1 Chain
Common mechanism : breaking of a singlet
Non magnetic impurity effects in cuprates
The normal state
doping
T
Antiferromagnetism Superconductivity
pseudogap
Why choosing YBaCuO ?
YBaCuO7 92 12 kHz
Impurity effects on doping and pseudogap
0 100 200 300 400 5000.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
pure Zn : xplane = 3% Zn : xplane = 6 %
Ks (%
)
T (K)
YBaCuO6.6
• No effect on doping• No effect on pseudogap
• Effect on resistivity :
Zn : strong scattering center Ni : weaker
•Effect on macroscopic susceptibility :
Zn induces an effective paramagnetic moment S<1/2which decreases with increasing dopingNi induces a moment ≠ S=1 (Mendels, 1994,1999; Zagoulaiev, 1995 )
Impurity effects on macroscopic properties
(Chien, 1991)
100 150 200 250 300 350
0
-100
-200
-300
2èmes voisins
raie centrale
1ers voisins
89K
(ppm
)
T (K)
89Y
100 200 300 4000
200
400
600
800
7 K (p
pm)
T (K)
x = 0.85 % / plane x = 1.8 % / plane
7Li
100 200 3000
20
40
T (K)
17Δν
(kH
z)
17O
Nonmagnetic Impurity in Pseudogap regime
Alloul,91;Walstedt,93;Mahajan,94; Williams,95; Ishida,97; JB,97,99; Julien,2000; Itoh,2003; Ouazi, 2004
0 2 4 6 80.000
0.002
0.004
0.006
Distance to the impurity (unit cells)
Spatial dependence Extension
⟨Sz ( r
) ⟩
T = 85K
Ouazi, 2004
Multi-nuclei quantitative analysis of the induced staggered polarization
100 1500
2
4
6
8
10
ξ (c
ell u
nits
)
Temperature (K)
ξimpurity
• Analogy with spin chains• Theoreticall justifications :
t-J (Poilblanc)RVB (Khaliullin, Gabay, Nagaosa & Lee)
Nonmagnetic Impurity in Pseudogap regime
Spatial dependence
⟨Sz ( r
) ⟩
T = 85K
Effect of hole doping on the induced polarization
0 2 4 6 80.000
0.002
0.004
0.006
Distance to the impurity (unit cells)
100 1500
1
2
3
4
5
6
7
ξ imp (u
nit c
ells)
Température (K)
dopage
• persistence of corrélations at optimal doping
NAFL, SCR (Bulut, Ohashi)
Extension
dopage
100 200 300 400
200
300
400
YBa2Cu3O6.97
YBa2Cu3O6.6
7 K (p
pm)
T (K)
0
400
800 x = 0.85 % / plane x = 1.8 % / plane
6.4 6.6 6.8 7.0 7.20
50
100
150
200
250
Tem
pera
ture
(K)
oxygen doping
0
5
10
C (M
Hz.
K)
Fit inC/(T+Θ)
Susceptibility on 1st near neighbor Cu C
Θ
Effect of hole doping on the induced polarization
JB, 1999
Impurity effects in cuprates
The superconducting state
doping
T
Antiferromagnetism Superconductivity
pseudogap
• Effect on TC :
only dependent on scattering potential (d-wave)
(Rullier-Albenque, 2000)
• Effect on penetration depth :
λ increases with impurity content,ns decreases with impurity content (Bonn, 1993;Bernhard, 1996)
Impurity effects in the superconducting state
Pan, Nature 2000 Hudson, Nature 2001
Impurity effects in the superconducting state
Bi2212 + Zn T = 4.2 K
Sidis, 1996
purZn 2%
Effect on local Density Of States
Effect on magneticresponse χ’’(QAF,ω)
close to Zn
far from Zn
500
1000
Li 1% Li 2%
T C1%T C
2%
Y Ba2Cu3O 6.97
7 K (p
pm)
1000
2000
3000
T C1%
Y Ba2C u3O 6.67 K
(ppm
)
0 40 80 120
400
600
T (K )
T C1%
Y Ba2Cu3O 7 Ca20%
7 K (p
pm)
JB, 2001
Impurity effects in the superconducting stateMagnetic effect on 1st near neighbor Cu of non magnetic Li
40350 40400 40450 40500 405500.0
0.5
1.0
xp=0 %
xp=6%xp=3%
xp=1.5%
Inte
nsity
(arb
itrar
y un
its)
ν (kHz)
Impurity effects in the superconducting state
Induced polarization by non Magnetic Zn or magnetic Ni
In-plane 17O NMR in YBaCuO7 (optimal doping) with Zn at T=10K
Ouazi et al., 2005
Impurity effects in the superconducting state
Induced polarization by non Magnetic Zn or magnetic Ni
In-plane 17O NMR in YBaCuO7 (optimal doping) with Zn at H = 7 Tesla
0 1 2 3 4 5 6 70
50
100
150
200
250
Zn in-plane concentration xP (%)
17O
full
wid
th a
t hal
f max
imum
(kH
z) field-independent contribution field-dependent contribution μSR vortex lattice field distribution
0 20 40
0
1000
2000
Temperature (K)
Zn : 1.5 %Zn : 3 %Zn : 6 %Ni : 2.25 %
ΔνH -
ΔνL (p
pm)
0 10 20 30 40 50 1000
1000
2000 Zn : 1.5 %Zn : 3 %Zn : 6 %Ni : 2.25 %
Temperature (K)
ΔνL (p
pm)
4 0 3 5 0 4 0 4 0 0 4 0 4 5 0 4 0 5 0 0 4 0 5 5 0
0 .5
1 .0
x p = 3 %
Inte
nsity
(arb
itrar
y un
its)
ν (k H z )
ΔνL ΔνH
ΔνH - ΔνLΔνL
Induced polarization by non Magnetic Zn or magnetic Ni below TC
0 10 20 30 40 50 1000
1000
2000 Zn : 1.5 %Zn : 3 %Zn : 6 %Ni : 2.25 %
Temperature (K)
Δν L (p
pm)
Induced polarization by non Magnetic Zn or magnetic Ni below TC
ΔνL
Staggered magnetization survives below TC for Zn and Ni
• Zn : no T-dependence – saturation of ξ ∼ 3 cells• Ni : Curie-Weiss T-dependence – local moment on Ni in the Ni case at least, coexistence between superconductivity and staggered magnetism
xp=3%
ΔνL ΔνH
Induced polarization by non Magnetic Zn or magnetic Ni below TC
New low temperature asymetry for Zn, not for Ni
0 20 40
0
1000
2000
Temperature (K)
Zn : 1.5 %Zn : 3 %Zn : 6 %Ni : 2.25 %
ΔνH -
ΔνL (p
pm)
ΔνH - ΔνL
Ouazi et al., 2005
• Local Space-Varying Density of States effect near EF
• Confirmation of STM measurements, in YBaCuO bulk
• T-dependence : sharp decrease when increasing T
• BCS + unitary scattering (Hirschfeld, Balatsky, Salkola, Flatté ...)
• RPA (Ohashi)
• t-J + d-wave superconductivity (Wang & Lee)
• Kondo (Povkolnikov, Vojta, Sachdev)
Some models for an impurity in the superconducting state
Normal state of cuprates : • Pseudogap analogous to low dimension
insulating spin systems : strong correlations• Optimal doping : still some correlations• Quantitative estimate of the polarization :
strong constraint for any microscopic model
Superconducting state : • Many features typical of an anisotropic BCS
superconductivity, especially DOS effects• Zn and Ni Induced moments very similar to
normal state• Coexistence of staggered moments and
superconductivity (Ni case)
Conclusions