When 3:30 PM - 5:00 PM Nov 13, 2009
Where 1670 CSE
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Increasing the Tc of Cuprate High Temperature Superconductors


Jamil Tahir-Kheli, California Institute of Technology

High temperature superconductivity in the cuprates was discovered in 1986 with Tc = 34K by Bednorz and Muller who doped the anti-ferromagnetic insulator, La2CuO4, with Ba to form La1-xBaxCuO4. YBa2Cu3O7-δ with Tc = 92K was discovered soon thereafter in 1987. By 1994, the highest cuprate superconducting temperature was increased to 138K in Hg0.8Tl0.2Ba2Ca2Cu3O8+δ.  No further increases in Tc have occurred in the past 15 years despite intense experimental and theoretical effort. In addition, the mechanism of superconductivity remains unknown. In this talk, we develop a novel new theory that can quantitatively explain a broad spectrum of cuprate phenomenology using only simple counting arguments. The theory is based upon the idea that doping leads to the formation of four-Cu-site plaquettes that percolate throughout the crystal.  The theory leads to a direct prediction on how to increase Tc by controlling the location of dopants in these materials. Our calculated solutions to the gap equation find that a 50% increase in Tc can occur by judicious doping rearrangement. This suggests that even higher Tc’s are possible in the cuprate class of superconductors.

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