Spin polaron theory for the photoemission spectra of layered cobaltates

TL;DR

This paper introduces a spin-polaron model to explain the unusual photoemission spectra of layered cobaltates, accounting for increased incoherence near the band insulator regime due to spin-state fluctuations.

Contribution

It presents a novel spin-polaron theoretical framework based on Co^{3+} spin-state quasidegeneracy to explain spectral features in layered cobaltates.

Findings

Reproduces the 'peak-dip-hump' spectral lineshapes observed experimentally.

Shows that spin-state fluctuations suppress quasiparticle coherence.

Explains increased incoherence near the band insulator regime.

Abstract

Recently, strong reduction of the quasiparticle peaks and pronounced incoherent structures have been observed in the photoemission spectra of layered cobaltates. Surprisingly, these many-body effects are found to increase near the band insulator regime. We explain these unexpected observations in terms of a novel spin-polaron model for CoO_2 planes which is based on a fact of the spin-state quasidegeneracy of Co^{3+} ions in oxides. Scattering of the photoholes on spin-state fluctuations suppresses their coherent motion. The observed ``peak-dip-hump'' type lineshapes are well reproduced by the theory.