Spin-dependent polaron formation dynamics in Eu$_{0.75}$Y$_{0.25}$MnO$_3$ probed by femtosecond pump-probe spectroscopy

TL;DR

This study uses femtosecond pump-probe spectroscopy to investigate spin-dependent polaron formation and ultrafast magnetic interactions in Eu$_{0.75}$Y$_{0.25}$MnO$_3$, revealing how optical excitations influence spin and orbital dynamics.

Contribution

It provides new insights into the ultrafast spin and polaron dynamics in multiferroic manganites, highlighting the role of superexchange interactions and orbital occupancy changes.

Findings

Ultrafast modulation of superexchange interactions observed.

Significant increase in photoinduced reflectance linked to spin correlations.

Decay of localized spin excitations occurs on tens of picoseconds.

Abstract

We present a femtosecond optical pump-probe study of the multiferroic manganite Eu$_{0.75}$Y$_{0.25}$MnO$_3$. The optical response of the material at pump energies of 1.55 and 3.1 eV is dominated by the $d$-$d$ and $p$-$d$ transitions of the Mn$^{3+}$ ions. The relaxation of photoexcited electrons includes the relaxation of the Jahn-Teller distortion and polaron trapping at Mn$^{2+}$ and Mn$^{4+}$ sites. Ultrafast switching of superexchange interactions due to modulated $e_g$ orbital occupancy creates a localized spin excitation, which then decays on a time scale of tens of picoseconds at low temperatures. The localized spin state decay appears as a tremendous increase in the amplitude of the photoinduced reflectance, due to the strong coupling of optical transitions to the spin-spin correlations in the crystalline $a$-$b$ plane.