Distinctive Picosecond Spin Polarization Dynamics in Bulk Half-Metals

TL;DR

This paper predicts and confirms unique picosecond spin dynamics in bulk half-metals induced by femtosecond laser excitation, revealing a long-lived non-equilibrium spin polarization state with potential for material characterization.

Contribution

It introduces a novel theoretical model describing long-lasting spin polarization in half-metals and validates it through femtosecond spectroscopy experiments on Fe$_3$O$_4$.

Findings

Long-lived non-equilibrium spin polarization above the Fermi energy.

Distinct thermalization process with three Fermi-Dirac distributions.

Robust spin polarization response useful for characterizing bulk half-metals.

Abstract

Femtosecond laser excitations in half-metal (HM) compounds are theoretically predicted to induce an exotic picosecond spin dynamics. In particular, conversely to what is observed in conventional metals and semiconductors, the thermalization process in HMs leads to a long living partially thermalized configuration characterized by three Fermi--Dirac distributions for the minority, majority conduction and majority valence electrons respectively. Remarkably, these distributions have the same temperature but different chemical potentials. This unusual thermodynamics state causes a persistent non-equilibrium spin polarization only well above the Fermi energy. Femtosecond spin dynamics experiments performed on Fe$_3$O$_4$ by time-, spin-, and angle-resolved photoelectron spectroscopy confirm our model. Furthermore, the spin polarization response proves to be very robust and it can be adopted to selectively test the bulk HM character in a wide range of compounds.