Subpicosecond metamagnetic phase transition driven by non-equilibrium electron dynamics

TL;DR

This study reveals that femtosecond laser pulses can induce a ferromagnetic phase in antiferromagnetic FeRh within subpicoseconds by altering electronic structures through non-thermal electron distributions and charge transfer.

Contribution

It combines time-resolved photoelectron spectroscopy with ab-initio calculations to elucidate the ultrafast, non-equilibrium processes driving the phase transition in FeRh.

Findings

Ferromagnetic order appears 350 fs after excitation.

Non-thermal electron distributions modify the electronic band structure.

Charge transfer from Rh to Fe initiates the phase transition.

Abstract

Femtosecond light-induced phase transitions between different macroscopic orders provide the possibility to tune the functional properties of condensed matter on ultrafast timescales. In first-order phase transitions, transient non-equilibrium phases and inherent phase coexistence often preclude non-ambiguous detection of transition precursors and their temporal onset. Here, we present a study combining time-resolved photoelectron spectroscopy and ab-initio electron dynamics calculations elucidating the transient subpicosecond processes governing the photoinduced generation of ferromagnetic order in antiferromagnetic FeRh. The transient photoemission spectra are accounted for by assuming that not only the occupation of electronic states is modified during the photoexcitation process. Instead, the photo-generated non-thermal distribution of electrons modifies the electronic band structure. The ferromagnetic phase of FeRh, characterized by a minority band near the Fermi energy, is established 350+- 30 fs after the laser excitation. Ab-initio calculations indicate that the phase transition is initiated by a photoinduced Rh-to-Fe charge transfer.