Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr2IrO4

Abstract

Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity. Recently, photo-excitation has been used to induce similarly exotic states transiently. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.

Towards properties on demand in quantum materials

“…At present, state-of-the-art ultrafast methods offer a near-complete characterization of the transient state 152 . Indeed, tr-ARPES provides a direct probe of the transient electronic structure 66,67,120,153 , tabletop and accelerator-based X-ray free-electron lasers readily capture momentary crystal arrangements 118,154 , nonlinear optical methods can directly interrogate the symmetries of quantum phases and their host lattices 30,[155][156][157][158] , while optical and soft X-ray techniques document electronic excitations, in some cases with elemental and orbital specificity 159 . Importantly, mesoscopic phenomena that are prevalent in quantum materials lead to new time and energy scales, as documented in various ultrafast studies 110,160 .…”

Femtosecond manipulation of spins, charges, and ions in nanostructures, thin films, and surfaces

“…1, we classified the relevant electronic and structural excitations of interest in materials on an energy/momentum landscape. Conventional ultrafast optical tools are mostly restricted to the exploration of the energy axis of this diagram, with some momentum resolution being allowed for example by diffraction or Raman-based techniques such as resonant inelastic X-ray Scattering (RIXS, only recently demonstrated with fs-resolution at a free electron laser 18,19 ) or impulsive stimulated Raman scattering (ISRS) 20,21 . Energy and momentum resolution can be readily obtained instead via time and angle resolved photoelectron spectroscopy (TR-ARPES) 22 …”

Femtosecond resonant magneto-optical Kerr effect measurement on an ultrathin magnetic film in a soft X-ray free electron laser

“…In previous studies, a number of attempts have been made using various phenomenological models, such as atomistic calculations, (quasi)particle-mediated spinflip mechanisms, [4][5][6] and a framework of the superdiffusive transport. 7) Recently, the study of femtomagnetism has targeted more complicated magnetic materials such as strongly correlated systems 8,9) and magnetic heterostructures 10,11) with more than two magnetic components. Ultrathin magnetic heterostructures consisting of a (non)magnetic metal or an oxide layer have become one of the nextgeneration material groups in the femtomagnetism for unraveling the effect of spin-orbit interactions that induce perpendicular magnetic anisotropy.…”