Fig. 4: Possible origin of phonon-driven enhancement of ferromagnetism.
From: Photo-induced high-temperature ferromagnetism in YTiO3
a, Temperature dependence of non-equilibrium magnetization for each pump excitation frequency (coloured circles). Error bars represent propagated uncertainty in M, as detailed in the Methods. b, The energy gap Δ between the orbital ground state \(| {\rm{GS}}\rangle \) and first excited orbital state \(| {\rm{ES}}\rangle \) for each of the three excited phonons. The experimental mode displacements are on the order of \(1\sqrt{u}{\rm{\mathring{\rm A} }}\) in magnitude (u, atomic mass units). c, Illustration of the equilibrium orbital ground state and the changes \(({| {\rm{GS}}\rangle }_{{\rm{pumped}}}-{| {\rm{GS}}\rangle }_{{\rm{equil.}}})\) induced by driving the 4 THz and 9 THz phonons. We propose that the structural and orbital changes push the system farther or closer to the phase boundary, respectively, thereby suppressing or enhancing detrimental spin fluctuations.
