Anomalous electron quasiparticle excitation spectrum in electron-doped cuprate superconductors

Within the framework of the kinetic energy-driven superconductivity, the complicated line shape in the electron quasiparticle excitation spectrum of the electron-doped cuprate superconductors is studied. It is shown that as in the hole-doped counterparts, the momentum and energy dependence of the quasiparticle scattering rate in the electron-doped cuprate superconductors has a well-pronounced peak structure at around the antinodal and nodal regions. However, this peak structure is absent from the hot spots. This special momentum and energy dependence of the quasiparticle scattering rate therefore generates a remarkable peak-dip-hump structure in the electron quasiparticle excitation spectrum of the electron-doped cuprate superconductors at around the antinodal and nodal regions except for at around the hot spots, where the peak-dip-hump structure is absent. The theory also indicates that there is a common physical origin for the peak-dip-hump structure both in the hole- and electron-doped cuprate superconductors.

Diffusion in generalized hydrodynamics and quasiparticle scattering

We extend beyond the Euler scales the hydrodynamic theory for quantum and classical integrable models developed in recent years, accounting for diffusive dynamics and local entropy production. We review how the diffusive scale can be reached via a gradient expansion of the expectation values of the conserved fields and how the coefficients of the expansion can be computed via integrated steady-state two-point correlation functions, emphasising that {\mathcal PT}𝒫T-symmetry can fully fix the inherent ambiguity in the definition of conserved fields at the diffusive scale. We develop a form factor expansion to compute such correlation functions and we show that, while the dynamics at the Euler scale is completely determined by the density of single quasiparticle excitations on top of the local steady state, diffusion is due to scattering processes among quasiparticles, which are only present in truly interacting systems. We then show that only two-quasiparticle scattering processes contribute to the diffusive dynamics. Finally we employ the theory to compute the exact spin diffusion constant of a gapped XXZ spin-1/2−1/2 chain at finite temperature and half-filling, where we show that spin transport is purely diffusive.