Electronic Specific Heat of La_<2-x>Sr_xCuO_4 : Pseudogap Formation and Reduction of the Superconducting Condensation Energy(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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To examine the so-called small pseudogap and the superconducting (SC) condensation energy U(0), the electronic specific heat C_<el> was measured on La_<2-x>Sr_xCuO_4 up to 〜120K. In samples with doping level p (= x) less than 〜0.2, small pseudogap behavior appears in the γ (= C_<el>/T) vs T curve around the mean-field critical temperature for a d-wave superconductor T_<co> (= 2Δ_0/(4-5)k_B), where Δ_0 is the maximum gap at T ≪ T_c. The condensation energy U(0) is largely reduced in the pseudogap regime (p 〓 0.2). The reduction of U(0) can be well reproduced by introducing an effective SC energy scale Δ^<eff>_0 = βpΔ_0 (β = 4.5) instead of Δ_0. The effective SC energy scale is discussed in relation to the coherent pairing gap formed over the nodal Fermi arc.
社団法人日本物理学会の論文
2004-08-15