Spin singlet and quasiparticle excitations in cuprate superconductors

We followed step by step the transition from an antiferromagnetic (AFM) Mott insulator to a superconducting (SC) metal in the Bi2Sr2CaCu2O8+sigma (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, delta(pg)(p), closely follows that of the SSE, delta(sse)(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 delta(max)(sc) and the SC transition temperature Tc are linked in an extended range of doping, such as delta(max)(sc)(p)( )proportional to delta(sse)(p) Tc (p). This relation suggests that the AFM correlations play a key role in the mechanism of superconductivity.

Automated summary

This study tracked the transition from an antiferromagnetic Mott insulator to a superconducting metal in the Bi-2212 cuprate using electronic Raman scattering spectroscopy. The features of the pseudogap phase developing during this transition were interpreted as the blocking of charge carriers by enhanced AFM correlations. The relation between the superconducting gap and transition temperature with AFM correlations suggests their key role in the mechanism of superconductivity.