Nature of Bosonic Excitations revealed by high-energy charge carriers

TL;DR

This paper demonstrates how high-energy charge carrier experiments can differentiate between phonons and magnons as bosonic excitations based on their energy absorption and relaxation dynamics.

Contribution

It introduces a method using time-resolved pump-probe experiments to distinguish between regular and hard-core bosonic excitations in materials.

Findings

Phonons can absorb unlimited energy, leading to fluence-independent relaxation.

Magnons exhibit energy storage limits, causing fluence-dependent relaxation times.

Multiple pulse experiments show similar effects in driven systems.

Abstract

We address a long standing problem concerning the origin of bosonic excitations that strongly interact with charge carriers. We show that the time-resolved pump-probe experiments are capable to distinguish between regular bosonic degrees of freedom, e.g. phonons, and the hard-core bosons, e.g., magnons. The ability of phonon degrees of freedom to absorb essentially unlimited amount of energy renders relaxation dynamics nearly independent on the absorbed energy or the fluence. In contrast, the hard core effects pose limits on the density of energy stored in the bosonic subsystems resulting in a substantial dependence of the relaxation time on the fluence and/or excitation energy. Very similar effects can be observed also in a different setup when the system is driven by multiple pulses of equal energy.