Electronic Specific Heat of La2-xSrxCuO4: Pseudogap Formation and Reduction of the Superconducting Condensation Energy

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 x CuO 4 up to ∼120 K. 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 (\( p\lesssim 0.2\)). The reduction of U (0) can be well reproduced by introducing an effective SC energy scale Δ 0 eff =β p Δ 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.