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Published on October 15, 2007

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High Temperature Superconductivity:  High Temperature Superconductivity Huan Yang Overview:  Overview Conventional Superconductivity Basic phenomena in high temperature superconductivity Current Studies on high temperature superconductivity High Temperature Superconductivity in the future Zero Resistivity:  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! Meissner Effect:  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. BCS Theory:  BCS Theory BCS=John Bardeen, Leon Cooper and Robert Schrieffer Paring of electron- Cooper Pairs 1972 Nobel Prize in Physics Copper Pair is stable:  Copper Pair is stable Copper assumes If |Ek-EF| and |Ek'-EF|<ħω otherwise Pairing State SchrÖdinger equation Copper Pair is Stable:  Copper Pair is Stable So we have Or E<0 !!! Field point of view:  Field point of view Ground State In ground state, all electrons are in pairs. Gap in the density of States:  Gap in the density of States Diagonalize the hamiltonian: S-wave gap function Type I and Type II superconductor:  Type I and Type II superconductor Type I Type II Vortex, supercurrent and superfluidity:  Vortex, supercurrent and superfluidity High temperature Superconductivity:  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 ). High Temperature Superconductor:  High Temperature Superconductor Crystal Structure of High temperature superconductors:  Crystal Structure of High temperature superconductors Hab Hc 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. What interactions/orders exist in High-Tc Superconductor? Phase Diagram and Competing Orders:  Phase Diagram and Competing Orders PG: Pseudogap, SC: Superconductivity, CO: Competing order, AFM: Antiferromagnetic Competing order in high-Tc superconductivity:  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. H-T Phase Diagram:  H-T Phase Diagram CO=Competing Orders a = doping level Coherent phase H-T Phase Diagram:  H-T Phase Diagram CO=Competing Orders Magnetic Irreversibility:  Magnetic Irreversibility Hg-1223 Magnetic Irreversibility (SQUID DATA):  Magnetic Irreversibility (SQUID DATA) H=2T T(Hirr) H=2T Hg-1223 Magnetic Susceptibility Technique:  Magnetic Susceptibility Technique Compare 1st harmonic result with literature:  Compare 1st harmonic result with literature Hg1223 (HgBa2Ca2Cu3Ox ) 1st Harmonic Signal YBa2Cu3O7−x M. Nikolo, Amer. J. of Phys., Vol. 63, Issue 1, 55-65 Coil Data:  Coil Data T(Hirr) Bulk Measurement for Magnetic Irreversible Field :  Bulk Measurement for Magnetic Irreversible Field Hc2 Hc2~355T H/HC2 Scanning Tunneling Microscopy:  Scanning Tunneling Microscopy Piezo-tube scanner and STM tip Sample V V=Bias voltage Scanning Tunneling Microscopy:  Scanning Tunneling Microscopy Topography Vbias=0.5V,Iset=0.63nA Au Scanning Tunneling Microscopy:  Scanning Tunneling Microscopy Spectroscopy dI/dV ∝ Density of States Slide29:  BCS Theory does not work D = 10.5 meV V = 3.8 meV Theory with SC & CO Nai-Chang Yeh et al. Quasiparticle Density of States and Competing Orders Spatial variation of SC Gap:  Spatial variation of SC Gap K.McElroy et al. PRL 94, 197005 (2005) High Tc in the future:  High Tc in the future Room temperature superconductor A satisfactory theory on High temperature superconductivity Development of superconductor devices Reference:  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 Physics 43, 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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