Spin-polaron band structure and hole pockets in underdoped cuprates

TL;DR

This paper introduces a variational string-based approach to analyze spin polarons in antiferromagnets, explaining various phenomena in underdoped cuprates such as Fermi surface features, pseudogap, and the waterfall effect.

Contribution

It provides a novel variational method to understand the internal structure and dispersion of spin polarons, linking microscopic theory to experimental observations in cuprates.

Findings

Explains the remnant Fermi surface in undoped compounds.

Accounts for hole pockets, Fermi arcs, and pseudogap in doped cuprates.

Describes the waterfall phenomenon through phase interference.

Abstract

We present a variational approach based on the string picture to analyze the internal structure and dispersion of spin polarons with different symmetries in an antiferromagnet. We then use this to discuss the properties of underdoped cuprate superconductor within the `doped insulator' picture. The theory explains the remnant Fermi surface for the undoped compunds, as well as hole pockets, Fermi arcs, high energy pseudogap and the the mid-infrared band in doped materials. Destructive interference between the phases of a photohole near $\Gamma$ and the internal phases of the Zhang Rice singlet combined with our theory moreover explains the `waterfall' phenomenon.