Electronic structure of underdoped cuprates

TL;DR

This paper investigates how the Fermi surface and spin-fermion interactions evolve in underdoped cuprates as coupling strength varies, revealing a transition from large to small Fermi pockets and altered vertex behavior, relevant to experimental observations.

Contribution

It provides a detailed theoretical analysis of the evolution of the Fermi surface and spin-fermion vertex in underdoped cuprates across different coupling regimes, connecting to experimental data.

Findings

Large Fermi surface at weak coupling

Small pockets at strong coupling

Reduced spin-fermion vertex at strong coupling

Abstract

We consider a two-dimensional Fermi liquid coupled to low-energy commensurate spin fluctuations. At small coupling, the hole Fermi surface is large and centered around $Q =(\pi,\pi)$. We show that as the coupling increases, the shape of the quasiparticle Fermi surface and the spin-fermion vertex undergo a substantial evolution. At strong couplings, $g \gg \omega_0$, where $\omega_0$ is the upper cutoff in the spin susceptibility, the hole Fermi surface consists of small pockets centered at $(\pm \pi/2, \pm \pi/2)$. Simultaneously, the full spin-fermion vertex is much smaller than the bare one, and scales nearly linearly with $|q-Q|$, where $q$ is the momentum of the susceptibility. At intermediate couplings, there exist both, a large hole Fermi surface centered at $(\pi,\pi)$, and four hole pockets, but the quasiparticle residue is small everywhere except for the pieces of the pockets which face the origin of the Brillouin zone. The relevance of these results for recent photoemission experiments in $YBCO$ and $Bi2212$ systems is discussed.