Unconventional properties of superconducting cuprates

Abstract

We present an explanation of the unusual peak/dip/hump features observed in photoemission experiments on Bi2212 at $T \ll T_c$. We argue that these features arise from the interaction of the fermionic quasi-particles with overdamped spin fluctuations. We show that the strong spin-fermion interaction combined with the feedback effect on the spin damping due to superconductivity yields a Fermi-liquid form of the fermionic spectral function for $ω< 2 Δ$ where $Δ$ is the maximum value of the superconducting gap, and a non-Fermi-liquid form for $ω> 2 Δ$. In the Fermi-liquid regime, the spectral function $A({\bf k}_F,ω)$ displays a quasiparticle peak at $ω= Δ$; in the non-Fermi-liquid regime it possesses a broad maximum (hump) at $ω\gg Δ$. In between the two regimes, the spectral function has a dip at $ω\sim 2 Δ$. We argue that our theory also explains the tunneling data for the superconducting density of states.