Unconventional properties of superconducting cuprates

TL;DR

This paper explains the unusual spectral features observed in photoemission experiments on cuprate superconductors by modeling their interaction with overdamped spin fluctuations, revealing a crossover from Fermi-liquid to non-Fermi-liquid behavior.

Contribution

It introduces a theory connecting spin fluctuations with spectral features in cuprates, explaining peak/dip/hump structures and tunneling data.

Findings

Spectral function shows a quasiparticle peak at the gap energy in Fermi-liquid regime.

Broad hump appears at higher energies in non-Fermi-liquid regime.

The theory accounts for tunneling density of states measurements.

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 $\omega < 2 \Delta$ where $\Delta$ is the maximum value of the superconducting gap, and a non-Fermi-liquid form for $\omega > 2 {\Delta}$. In the Fermi-liquid regime, the spectral function $A({\bf k}_F,\omega)$ displays a quasiparticle peak at $\omega = {\Delta}$; in the non-Fermi-liquid regime it possesses a broad maximum (hump) at $\omega \gg {\Delta}$. In between the two regimes, the spectral function has a dip at $\omega \sim 2 {\Delta}$. We argue that our theory also explains the tunneling data for the superconducting density of states.