Study on Electronic Specific Heat of LA2-xSRxCUO4; Pseudogap and Superconductivity
In high-Tc cuprates it is strongly suggested that the phase diagram is characterized by two kinds of crossover temperatures Tmax(T0) and T*(Tc < T* < Tmax [1,2]. Intensive studies on the crossover phenomena around Tmax and T* have been performed to understand the anomalous normal state and clarify the mechanism of the superconductivity. The magnetic susceptibility x in Bi2Sr2CaCu2O8 (Bi2212) and La2-xSrxCuO4 (La214), following the Curie-Weiss law at T ≫ T max , gradually decreases at T < T max [3-5]. Detailed analyses on the x-T curves have revealed that the energy scale k B T max gives the effective antiferromagnetic (AF) exchange energy J eff between Cu 3d-spins and the gradual decrease of x at T < T max is due to the development of a (short range) AF correlation [3-5]. Recently angle-integrated photoemission spectroscopy (AIPES) has revealed that a gap-like structure, namely a pseudogap (PG), progressively develops over a wide T-range below T max . The PG has the energy scale characterized by J eff ; that is, the spectral weight is depressed over the energy region of J eff around E f . These facts indicate that the PG evolution will be closely related to the development of the AF correlation.
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