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High-Temperature Superconductivity: Principles and Future Directions

This overview discusses high-temperature superconductivity, highlighting its evolution from the first discovery in mercury (1911) to significant breakthroughs such as the discovery of YBCO (1987) and Hg-1223 (highest Tc=135K). It covers conventional superconductivity, the fundamental phenomena involved, and the current studies surrounding competing orders and electron-phonon interactions. Additionally, it explores future prospects, including room-temperature superconductors and advancements in superconducting devices.

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High-Temperature Superconductivity: Principles and Future Directions

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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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