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1
Disorder, Superconducting fluctuations and
Metal-Insulator crossover in high Tc cuprates
F. Rullier-Albenque1, H. Alloul2, 1 Service de
Physique de lEtat Condensé, CEA, Saclay, France
. 2 Physique des Solides, Université Paris-Sud ,
Orsay, France F. Balakirev3, C. Proust4 3 NHMFL,
Los Alamos National Laboratory, New Mexico, USA 4
Laboratoire National des Champs Magnétiques
Pulsés, Toulouse, France

• Single crystals of YBCO P. Lejay (Grenoble), D.
  Colson, A. Forget (SPEC)

500mm

• Electron irradiation
• Laboratoire des Solides Irradiés
• (Ecole Polytechnique)

2
Disorder, Superconducting fluctuations and
Metal-Insulator crossover in high Tc cuprates

• Introduction
• Generic phase diagram of the cuprates
• Presence of incipient disorder?

• Influence of controlled disorder on Tc, T and
  the MIC of YBCO
• Zn substitution
• Electron irradiation

• Superconducting fluctuations, Nernst effect and
  magnetoresistance
• SC fluctuations in  pure  YBCO
• Influence of disorder

• Conclusion
• Phase diagram including disorder

3
 Generic  phase diagram of the cuprates?
This shape of phase diagram is apparently
generic But only established in the particular
case of La2-xSrxCuO4 x hole doping
4
Some questions about High Tc cuprates
Magnetic fluctuations
Pseudogap Phase transition? Crossover? Link
with superconductivity?
PG
Strange metal
Pseudogap joins Tc curve or QCP ??
underdoped
AF
optimal
Transition to a Fermi liquid?
T
overdoped
c max

SC
0
0.1
0.2
0.3
Number of holes/ CuO2 plane
Metal-Insulator transition
Importance of magnetic correlations at least for
underdoped materials
5
Anomalous Nernst effect in the normal state of
cuprates
La2-x Srx Cu O4
Tc
Effect more pronounced in underdoped samples
Significant Nernst signal at TgtTc
Signature of superconducting fluctuations in
the normal state Tc loss of long range phase
coherence
Possible implications for the physics of the
pseudogap regime preformed pairs?
Wang et al, PRB 64 (2001)
6
Metal Insulator crossover in low Tc cuprates?
low Tc cuprates LaSrCuO La-Bi2201
Low T upturns in r(T)
High magnetic field to suppress superconductivity
Ono et al, PRL 2000

• Role of intrinsic disorder?

7
Native disorder in the pure cuprate families
The optimum Tc and the residual resistivity r0
depend on the family
Disorder is detrimental to superconductivity Some
uncontrolled disorder is present in LSCO and
Bi2201
8
Comparison of the one layer cuprate families
YBCO7 20 of Ks
9
Disorder, Superconducting fluctuations and
Metal-Insulator crossover in high Tc cuprates

• Introduction
• Generic phase diagram of the cuprates
• Presence of incipient disorder?

• Influence of controlled disorder on Tc, T and
  the MIC
• Zn substitution
• Electron irradiation

• Superconducting fluctuations, Nernst effect and
  magnetoresistance
• SC fluctuations in  pure  YBCO
• Influence of disorder

• Conclusion
• Phase diagram including disorder

10
Influence of defects on the phase diagram
H. Alloul et al, PRL (1991)
4Zn
No change of hole doping No change of T
Tc decreases more rapidly in underdoped samples
Increase of the disordered magnetism range
11
Low T electron irradiation
Electron irradiation
Point defects homogeneously distributed Elastic
collisions between electrons and target nuclei
Cryostat coupled to a Hydrogen
cryogenerator Irradiation at 20K
No diffusion of defects
12
Influence of irradiation defects on the transport
properties
Optimally doped
overdoped
Same single crystals
F. Rullier Albenque et al, Europhysics Letters
50, 81 (2000), PRL (2003)
13
Resistivity upturns MIC?
F. Rullier-Albenque et al , Europhysics Letters
(2008).
Tc25K
14
Resistivity upturns MIC?
15
Resistivity upturns vs defect contents in YBCO6.6
In-situ measurements
16
In overdoped samples 2D weak localization
effects induced by disorder
Underdoped YBCO6.6 compared to overdoped Tl2201
For kFlegtgt1 (R2Dltlt26kW)
rin(T) T p
Overdoped Tl2201
Rullier-Albenque et al, PRL 87 (2001)
Purely elastic scattering by the defects
17
Spin glass phase and MIC in the Phase Diagram
SG and MIC are determined by disorder
18
Irradiated YBCO compared to  pure low Tc
Cuprates
The upturns are quantitatively similar Driven by
disorder
Controlled disorder Introduced in a pure system
Specific disorder reduces Tc
F. Rullier-Albenque et al , Europhysics Letters
81, 37008 (2008).
19
The various cuprate families in the phase diagram
20
Disorder, Superconducting fluctuations and
Metal-Insulator crossover in high Tc cuprates

• Introduction
• Generic phase diagram of the cuprates
• Presence of incipient disorder?

• Influence of controlled disorder on Tc, T and
  the MIC
• Zn substitution
• Electron irradiation

• Superconducting fluctuations, Nernst effect and
  magnetoresistance
• SC fluctuations in  pure  YBCO
• Influence of disorder

• Conclusion
• Phase diagram including disorder

21
Nernst effect in pure YBCO6.6
Rapid drop of the Nernst signal at Tc
22
Temperature extension of the Nernst signal in
pure YBCO
Optimally doped YBCO
Underdoped YBCO
Tonset
Tonset
The temperature range of the Nernst signal
increases with decreasing doping BUT Tonset is
higher in optimally doped than in underdoped YBCO
In pure YBCO6.6, the Nernst signal extends up to
85K much lower that the pseudogap temperature
T 300K
23
Transverse magnetoresistivity in YBCO7 High field
measurements
Magnetoresistance in the normal state
Harris et al. PRL (1995)
In YBCO7 Onset of SC fluctuations around 140K
24
Phase diagram of pure YBCO
How the range of superconducting fluctuations is
altered by disorder ?
25
Nernst effect in irradiated YBCO
YBCO6.6
F. Rullier-Albenque et al, PRL (2006)
26
Disorder and superconducting fluctuations in
YBCO6.6
Magnetoresistance data for the Tc6K sample
F. Rullier-Albenque et al, PRL (2007)
27
Disorder and superconducting fluctuations in
YBCO6.6
Comparison with Nernst results
With decreasing Tc
BUT remain quite large
28
Comparison between La-Bi2201 and irradiated
YBCO6.6
 Pure  underdoped Bi2 Sr2-y Lay Cu O6 y0.5 -
Tc 28.9K
Wang et al, PRB 64 (2001)
Tonset 75K
Electron irradiated YBCO6.6 Tc 24.6K (onset of
magnetization)
29
Disorder, Superconducting fluctuations and
Metal-Insulator crossover in high Tc cuprates
Disorder
Low T upturns of resistivity Not necessarily a MIC
Increase of the regime of superconducting
fluctuations
Spin glass, MIC , Tc The different cuprate
famlies
Pseudogap and fluctuation regime