Superconducting Condensation Energy and Pseudogap Formation in La_2-xSr_xCuO_4 : New Energy scale for Superconductivity(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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The electronic specific heat C_el was measured for La_2-xSr_xCuO_4 to examine the superconducting condensation energy at T = 0, U_0. We reconfirmed that U_0 is markedly reduced even in slightly underdoped samples whose T_c's are still more than 30 K. The reduction of U_0 results from the suppression of the effective superconducting gap,in addition to that of the density of states at the Fermi level E_F,caused by the pseudogap formation in the normal state. The doping-level (p) dependence of U_0 as well as T_c can be explained over a wide p range by introducing an effective energy gap Δ_eff=βpΔ_0 (β=4.5) instead of Δ_0,where Δ_0 is the maximum gap at T ≪T_c.
社団法人日本物理学会の論文
2002-12-15