Laser ARPES, the sudden approximation, and quasiparticle-like peaks in Bi2Sr2CaCu2O8+delta

TL;DR

This paper introduces a laser-based ARPES technique at low photon energies to study Bi2Sr2CaCu2O8+delta, revealing sharp quasiparticle peaks in the normal state and demonstrating robustness of key spectral features.

Contribution

It presents a novel low photon energy ARPES method that enhances bulk sensitivity and resolution, providing clearer evidence for quasiparticles in the normal state of a high-temperature superconductor.

Findings

Observation of sharp spectral peaks indicating quasiparticles

Robustness of dispersion and superconducting gap features

Identification of bosonic coupling kink and weight transfer

Abstract

A new low photon energy regime of angle resolved photoemission spectroscopy is accessed with lasers and used to study the superconductor Bi2Sr2CaCu2O8+delta. The low energy increases bulk sensitivity, reduces background, and improves resolution. With this we observe spectral peaks which are sharp on the scale of their binding energy - the clearest evidence yet for quasiparticles in the normal state. Crucial aspects of the data such as the dispersion, superconducting gaps, and the bosonic coupling kink and associated weight transfer are robust to a possible breakdown of the sudden approximation.