Bogoliubov Angle, Particle-Hole Mixture and Angular Resolved Photoemission Spectroscopy in Superconductors

TL;DR

This paper introduces the Bogoliubov angle as a new observable in ARPES that quantifies the particle-hole mixture in superconducting quasiparticles, enabling better understanding of superconducting excitations.

Contribution

It proposes a novel measurable quantity, the Bogoliubov angle, which captures particle-hole entanglement in superconductors and can be experimentally determined via spectral intensity ratios.

Findings

The Bogoliubov angle quantifies particle-hole mixture in superconductors.

It can be measured through spectral intensity ratios at positive and negative energies.

This approach offers new insights into superconducting quasiparticle properties.

Abstract

Superconducting excitations -- Bogoliubov quasiparticles -- are the quantum mechanical mixture of negatively charged electron (-e) and positively charged hole (+e). We propose a new observable for Angular Resolved Photoemission Spectroscopy (ARPES) studies that is the manifestation of the particle-hole entanglement of the superconducting quasiparticles. We call this observable a {\em Bogoliubov angle}. This angle measures the relative weight of particle and hole amplitude in the superconducting (Bogoliubov) quasiparticle. We show how this quantity can be measured by comparing the ratio of spectral intensities at positive and negative energies.