Spin singlet and quasiparticle excitations in cuprate superconductors

Abstract

We followed step by step the transition from an antiferromagnetic (AFM) Mott insulator to a superconducting (SC) metal in the Bi2Sr2CaCu2O8+δ (Bi-2212) cuprate using electronic Raman scattering spectroscopy. This was achieved by tracking the doping dependence of the spin singlet excitation (SSE) originating from the AFM Mott insulator, the normal-state quasiparticle excitation related to the mobile charge carriers, and the Bogoliubov quasiparticles related to the SC gap. We show that the signature of the pseudogap phase which develops during this transition can be interpreted as the blocking of charge carriers by the enhancement of the AFM correlations as the temperature drops. We find that the energy scale of the pseudogap, Δpg(p), closely follows that of the SSE, Δsse(p) with doping p. The quasiparticle lifetime considerably increases with doping when the pseudogap collapses. We reveal that the maximum amplitude of the SC gap Δscmax and the SC transition temperature Tc are linked in an extended range of doping, such as Δscmax(p)∝Δsse(p)Tc(p). This relation suggests that the AFM correlations play a key role in the mechanism of superconductivity.

Source-reported materials — not catalogue approval

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