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HTSC Yuval Lubashevsky Prof. Amit Keren The superconductor energy - PowerPoint PPT Presentation

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The origin of pseudogap in HTSC Yuval Lubashevsky Prof. Amit Keren The superconductor energy gap The BCS superconductor The pseudogap temperature Timusk Rep. Phys. 62 61-122 1999 NMR Resistivity Specific heat T c T* overdoped

  1. The origin of pseudogap in HTSC Yuval Lubashevsky Prof. Amit Keren

  2. The superconductor energy gap The BCS superconductor

  3. The pseudogap temperature Timusk Rep. Phys. 62 61-122 1999 NMR Resistivity Specific heat T c T* overdoped underdoped Takagi H PRL 69 2975 1992 Bankay M Loram J W T* PRB 50 Physica C 6416 1994 282-287 1405 1997

  4. ARPES measurements Theory Theory dSC state Normal state Experiment Experiment PG state dSC Kanigel

  5. Main question What are the interactions that affect the T*?

  6. The CLBLCO system    Ca La Ba La Cu O    x 1 x 1.75 x 0.25 x 3 y • Similar structure as the well known YBCO • 1:2:3 atomic ratio • The main structure doesn’t change with the families • Controllable doping level (y parameter) • Controllable magnetic coupling (x parameter)

  7. CLBLCO phase diagram • Similar phase diagrams 450 T c 400 T N 350 • The family with the T g 300 250 highest T c have the T (K) 200 80 highest T N on the x=0.1 lowest doping. 40 x=0.2 x=0.3 x=0.4 0 6.6 6.9 7.2 • Big difference at T c y max between the families Ofer PRB 73 220508 2006

  15. Transformation of the entire doping range.      opt opt p p p K ( y y ) (Ca x La 1-x )(Ba 1.75-x La 0.25+x )Cu 3 O y m x x 7 420 T N ,T g T c x x 6 T N 360 0.1 0.1 5 300 0.2 0.2 4 3 0.3 240 0.3 2 T N, g, C (K) 0.4 0.4 180 max T N, g, C / T C T C 80 1.0 60 T g 40 0.5 20 0 0.0 6.4 6.6 6.8 7.0 7.2 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 y  P m  max T , T , T T , T , T / T N g c N g c c   y K ( x ) y The scaling works in the entire doping range apart for x=0.1 ? Ofer PRB 73 220508 2006

  16. The role of anisotropies • T N is determined by the in-plane J and out of plane coupling. J  • We extracted J out of T N . Unified Phase Diagram 20 x=0.1 x=0.2 x=0.3 15 x=0.4 max 10 ( J, T g,c ) / T c 1.2 0.8 0.4 0.0 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1  P m . The in-plane J is extracted from T N Ofer PRB 73 220508 2006

  17. Scaling Conclusion • We found that T c scale like the in-plane J therefore is a consequence of a 2D magnetic interaction.  T J c • Question: Does T* scales with J as T c does, or with some other magnetic parameter?

  18. The experimental methods • The SQUID (Superconducting QUantum Interference Device) • The temperature range is 1.2K to 310K • The field range is up to 6.5T.

  19. Susceptibility  M   • Definition lim H   0 0 H   M H • Practice dc • Where D is known as the demagnetizing factor, and it get different values  for different geometries.    0  dc 1 D 0 • For needle like sample D=0, then:    dc 0

  20. Measurement condition   [cm  H  10 1 kG =1.809  3 /gm]   [cm 3 /gm]  H  10 -2 kG =2.571  Geometric dependence 6 -9 emu] 0 9 -40 0 40 M[10 1.0 0.5 8 0.0 -6 -0.5 7 3 /gr] -1.0 -7 cm 6 4 0.0 4 -4.0x10 4.0x10  [10 H [G] 5 Field dependence 4 3 0 1 2 3 4 5 h/2R

  21. Raw data This phenomena y=7.007 12 has been noticed y=6.93 y=6.87 by D C Johnston 10 y=6.75 on 1988 3 /gr] 8 -7 cm 3.8 6  [10 3.6 • The minimum point 3.38 3 /gr] 3.4 4 -7 cm drop systematically 3 /gr] 3.36 3.2  [10 -7 cm with the doping- first 3.0  [10 3.34 2 y=7.007 clue of pseudogap effect y=6.93 0 60 120 180 240 300 2.8 y=6.87 3.32 X=0.2 y=6.75 y=6.93 ( T* behavior). T [K] 180 240 300 T [K] 200 250 300 T [K]

  22.   f y ( ) 0 4.5 T  299 o K 3 /gr] 4.0 -7 cm 3.5  [10 x=0.1 3.0 x=0.2 x=0.3 x=0.4 2.5 2.0 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7.0 7.1 7.2 Y  • The value of is increasing with the doping (Pauli susceptibility).

  23. Susceptibility types • Isolated spin: Langevin paramagnetism, Curie law  2 N C    B 0 3 k T T B • Weakly coupled spins: Curie-Weiss C     0 T • Pauli spin (Landau ) :      2 0 ( ) T const D ( ) B f • Core: Van Vleck and Langevin   0 ( ) T const There is no traditional theory about increasing susceptibility with T

  24. Strongly coupled spins • Two coupled spins according to Heisenberg model.  2       J J        e 2 cosh 0     2 0.2 pseodogaped fitting function • shrinking arcs phenomena.   2   2 T T      A T ( )     J  0.1 0   * * T T   • The fitting term. shrinking arcs function strong coupled spins function const   0.0   0.0 0.1 0.2 0.3 0.4 0.5 0.6 0 T *   cosh k B T/J   T

  25. The fitting function C C     1 2 C     0 3 T * T   cosh   T C.W. + PG + CORE 12 C.W. Peudogap 3.60 10 core 3 /gr] 8 3.56 -7 cm   [10 6 3.52 160 200 240 280 4 0 100 200 300 T T [K]

  26. Curie-Weiss temperature       2 S S 1       Z J i i  3 K i B T  T N Antiferromagnetic susceptibility 0.6 40 x=0.1 x=0.1 x=0.2 x=0.2 0.5 x=0.3 x=0.3 30 x=0.4 x=0.4 0.4 max  [K] 0.3 20  /T c 0.2 10 0.1 0 0.0 -0.25 -0.20 -0.15 6.80 -0.10 6.85 -0.05 6.90 6.95 7.00 7.05 7.10  P m y

  27. T* 24 4 x=0.1 x=0.1 22 x=0.1 x=0.2 x=0.2 x=0.2 600 20 x=0.3 x=0.3 x=0.3 x=0.4 x=0.4 18 3 x=0.4 16 max max T* [K] T*/T N T*/T c 14 400 12 2 10 8 200 1 6 6.85 6.90 6.95 7.00 7.05 -0.2 -0.1 0.0 -0.25 -0.20 -0.15 -0.10 -0.05 y  P m  P m 7 x 6 0.1 5 0.2 4 3 0.3 The T* doesn ’ t scale well with T c . 2 0.4 max T N, g, C / T C T* scale with T N 1.0 0.5 Very similar to the T c /T N scaling. 0.0 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1  P m

  28. Conclusions We added the T* to the phase diagram T* scale like T N , and it is a 3D magnetic phenomena. T c is a 2D magnetic phenomena. 700 1.2 T c 600 1.0 T N 500 0.8 T g max 400 * /T N * 0.6 T 300 T c , T N , T g , T T (K) 200 0.2 * T c 80 x T N /T g T 0.4 x=0.1 0.1 0.3 40 x=0.2 0.2 x=0.3 0.1 x=0.4 0.0 0 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 6.3 6.6 6.9 7.2  P m y

  29. Acknowledgment I’m grateful to Prof. Amit Keren Thanks to: Dr. Arkady Knizhnik, Avi Post, Dr.Michael Reisner, Dr. Leonid Iomin And the lab’s fellow -students: Orenstein, Oren, Eran, Meni, Oshri, Daniel, Maniv, Gil, Yoash, Ana Specially to Rinat Ofer for her help

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