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High Temperature Superconductivity

High Temperature Superconductivity. Huan Yang. Overview. Conventional Superconductivity Basic phenomena in high temperature superconductivity Current Studies on high temperature superconductivity High Temperature Superconductivity in the future. Zero Resistivity. 1908- liquefied helium

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High Temperature Superconductivity

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  1. High Temperature Superconductivity Huan Yang

  2. Overview • Conventional Superconductivity • Basic phenomena in high temperature superconductivity • Current Studies on high temperature superconductivity • High Temperature Superconductivity in the future

  3. Zero Resistivity • 1908- liquefied helium • First discovered in mercury by Kamerlingh-Onnes in 1911. • Critical temperature 4.21K. • Nobel Prize in 1913. E=0 inside the superconductor!

  4. Meissner Effect • B=0 inside the superconductor • Superconductor is not just perfect conductor! • Supercurrent flowing around the surface to shield the B field. • Supercurrent is a superfluid.

  5. BCS Theory • BCS=John Bardeen, Leon Cooper and Robert Schrieffer • Paring of electron- Cooper Pairs • 1972 Nobel Prize in Physics

  6. Copper Pair is stable Pairing State SchrÖdinger equation If |Ek-EF| and |Ek'-EF|<ħω Copper assumes otherwise

  7. Copper Pair is Stable • So we have • Or E<0 !!!

  8. Field point of view Ground State In ground state, all electrons are in pairs.

  9. Gap in the density of States Diagonalize the hamiltonian: S-wave gap function

  10. Type I and Type II superconductor Type I Type II

  11. Vortex, supercurrent and superfluidity

  12. High temperature Superconductivity • Discovered by Johannes Georg Bednorz and Karl Alexander MÜller in LaBaCuO in 1986. Tc=35K. • Nobel Prize in 1987. • YBCO (YBa2Cu3O7-x) with Tc =95K was discovered in 1987. • Highest Tc we have today is 135K, in Hg1223 (HgBa2Ca2Cu3Ox).

  13. High Temperature Superconductor

  14. Crystal Structure of High temperature superconductors Hc Hab

  15. What interactions/orders exist in High-Tc Superconductor? • Electron-phonon interaction • Spin exchange interaction-antiferromagnetic order • Charge density waves, spin density waves and other competing orders.

  16. Phase Diagram and Competing Orders PG: Pseudogap, SC: Superconductivity, CO: Competing order, AFM: Antiferromagnetic

  17. Competing order in high-Tc superconductivity Competing Orders & Superconductivity Macroscopic Properties Microscopic Properties K.McElroy et al. PRL 94, 197005 (2005) Effect of competing orders on thermodynamic properties. • Local (~5nm) variation in the • Superconducting gap, Δ.

  18. H-T Phase Diagram Coherent phase CO=Competing Orders a = doping level

  19. H-T Phase Diagram CO=Competing Orders

  20. Magnetic Irreversibility Hg-1223

  21. Magnetic Irreversibility (SQUID DATA) T(Hirr) H=2T H=2T Hg-1223

  22. Magnetic Susceptibility Technique

  23. Compare 1st harmonic result with literature 1st Harmonic Signal YBa2Cu3O7−x Hg1223 (HgBa2Ca2Cu3Ox) M. Nikolo, Amer. J. of Phys., Vol. 63, Issue 1, 55-65

  24. Coil Data T(Hirr)

  25. Hc2 Bulk Measurement for Magnetic Irreversible Field H/HC2 Hc2~355T

  26. Scanning Tunneling Microscopy Piezo-tube scanner and STM tip V=Bias voltage V Sample

  27. Scanning Tunneling Microscopy Topography Vbias=0.5V,Iset=0.63nA Au

  28. Scanning Tunneling Microscopy Spectroscopy dI/dV ∝ Density of States

  29. Mean-field (SC & CDW) Exp. data weaker fluctuations Best BCS fitting stronger fluctuations normalized spectra Quasiparticle Density of States and Competing Orders Theory with SC & CO BCS Theory does not work D = 10.5 meV V = 3.8 meV Nai-Chang Yeh et al.

  30. Spatial variation of SC Gap K.McElroy et al. PRL 94, 197005 (2005)

  31. High Tc in the future • Room temperature superconductor • A satisfactory theory on High temperature superconductivity • Development of superconductor devices

  32. Reference • [1] Michael Tinkham, Introduction to superconductivity, chapter 1 • [2] H. Kamerling Onnes, Leiden Comm.120b,122b,124c (1911) • [3] J. G. Bednorz and K. A. Müller, Z. Physik, B 64, 189 (1986) • [4] N.-C. Yeh, Bulletin of the Association of Asia Pacific Physical Societies v.12 no.2, pp. 2-20 (2002), also cond-mat/0210656. • [5] A. D. Beyer, V. S. Zapf, H. Yang, M. S. Park,K. H. Kim, S.-I. Lee, and N.-C. Yeh. Submitted to Phys. Rev. Lett.; cond-mat/0612380. • [6] N.-C. Yeh, C.-T. Chen, V. S. Zapf, A. D. Beyer, C. R. Hughes, M.-S. Park, K.-H. Kim, and S.-I. Lee. Chinese Journal of Physics43, 505 Suppl. (2005), also cond-mat/0408105. • [7] J. Orenstein and A. J. Millis, Science 288, 468 (2000) • [8] S. Sachdev, Science 288, 475 (2000) • [9] E. Demler et.al. Phys. Rev. Lett. 87, 067202

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