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

1. Disorder, Superconducting fluctuations and Metal-Insulator crossover in high Tc cuprates F. Rullier-Albenque1, H. Alloul2, 1 Service de Physique de l’Etat 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? Magnetic fluctuations PG Strange metal underdoped AF optimal T overdoped c max SC SG 0.1 0.2 0.3 0 Number of holes/ CuO2 plane Hole doping not always very well determined The optimal Tc is not generic Thisshapeof 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 Transition to a Fermi liquid? optimal T overdoped c max SC 0.1 0.2 0.3 0 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 T>Tc 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? 60T 30T Metal-Insulator transition • Induced by the magnetic field • Competition between AF and SC 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. 5 Bi-2201 4 r / ) La-Bi2201 W (k 3 2D R YBCO 2 7 r0 1 T (K) 0 0 50 100 150 200 250 300 Correlation between r0 and optimum Tc Native disorder in the pure cuprate families The optimum Tc and the residual resistivity r0depend on the family Disorder is detrimental to superconductivity Some uncontrolled disorder is present in LSCO and Bi2201

8. Planar 17O NMR linewidths at optimal doping 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 Phase diagram including disorder T* The position of the optimal Tc shifts with disorder H. Alloul et al, PRL (1991) + 4%Zn No change of hole doping No change of T* Increase of the disordered magnetism range Tc decreases more rapidly in underdoped samples

11. Low T electron irradiation Different from : Proton irradiation Heavy ion irradiation Cluster of defects , columnar defects Vortex pinning studies 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. Dr The transition curves remain very sharp Homogeneous damage Matthiessen’s rule well obeyed at high T : D Tc Excellent control of defect content down to Tc =0 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. 55T High field suppresses SC and reveals upturns in irradiated samples Metallic behavior in pure YBCO6.6 Upturns related to the presence of defects F. Rullier-Albenque et al , Europhysics Letters (2008). Resistivity upturns= MIC? Tc=25K

14. 4% 3% 1.5% Matthiessen’s rule well obeyed 8% at high T : Log(1/T) behavior at high enough T Downward deviations in some cases Resistivity upturns = MIC?

15. Resistivity upturns vs defect contents in YBCO6.6 1.5 kW/ 2.2 3.0 3.8 4.8 For low defect content : r2D < 5kW/ Dr scales with r0 Dr saturates at low T Kondo like scattering on defects In-situ measurements

16. 1 0.1 T/T0 Underdoped YBCO6.6 compared to overdoped Tl2201 In overdoped samples 2D weak localization effects induced by disorder For kFle>>1 (R2D<<26kW) 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 Phase diagram in the absence of disorder ?

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 YBCO6.6 Tc=57K T onset : 85K 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 Transverse magnetoresistance under high magnetic fields H’c Magnetoresistance in the normal state Harris et al. PRL (1995) In YBCO7 Onset of SC fluctuations around 140K

24. Phase diagram of pure YBCO T* YBCO Tc Tc Nernst Onset of fluctuations follows Tc and not T* How the range of superconducting fluctuations is altered by disorder ?

25. Nernst effect in irradiated YBCO Comparaison YBCO6.6 and YBCO7 Tc=5K Tc=30K Tc=57K In both compounds the T range of the Nernst signal expands with disorder Effect more pronounced in underdoped YBCO6.6 Tonset is nearly the same for all the samples YBCO6.6 F. Rullier-Albenque et al, PRL (2006)

26. Disorder and superconducting fluctuations in YBCO6.6 Vortex solid Tc Magnetoresistance data for the Tc=6K sample F. Rullier-Albenque et al, PRL (2007)

27. Disorder and superconducting fluctuations in YBCO6.6 Tc systematically higher than Tn and are depressed Comparison with Nernst results With decreasing Tc BUT remain quite large

28. Comparison between La-Bi2201andirradiated YBCO6.6 Hc2 is nearly unchanged from low T to above Tc Tc = 28K Irradiated YBCO6.6 Tc = 25K Wang et al, PRB (2006) « Pure » underdoped Bi2 Sr2-y Lay Cu O6 y=0.5 - 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