Femtosecond electron diffuse scattering data of black phosphorus measured at the Fritz Haber Institute in Berlin. The dataset contains an experiment at 100 K (measurement _1.h5) .
The microscopic origin of slow carrier cooling in lead-halide perovskites remains debated, and has direct implications for applications. Slow carrier cooling has been attributed to either polaron formation or a hot-phonon bottleneck effect at high excited carrier densities (> 10$^{18}$ cm$^{-3}$). These effects cannot be unambiguously disentangled from optical experiments alone. However, they can be distinguished by direct observations of ultrafast lattice dynamics, as these effects are expected to create qualitatively distinct fingerprints. To this end, we employ femtosecond electron diffraction and directly measure the sub-picosecond lattice dynamics of weakly confined CsPbBr$_3$ nanocrystals following above-gap photo-excitation. The data reveal a light-induced structural distortion appearing on a time scale varying between 380 fs to 1200 fs depending on the excitation fluence. We attribute these dynamics to the effect of exciton-polarons on the lattice, and the slower dynamics at high fluences to slower hot carrier cooling, which slows down the establishment of the exciton-polaron population. Further analysis and simulations show that the distortion is consistent with motions of the [PbBr$_3$]$^{-}$ octahedral ionic cage, and closest agreement with the data is obtained for Pb-Br bond lengthening. Our work demonstrates how direct studies of lattice dynamics on the sub-picosecond timescale can discriminate between competing scenarios, thereby shedding light on the origin of slow carrier cooling in lead-halide perovskites.
The prototypical magnetic memory shape alloy Ni_{2}MnGa undergoes various phase transitions as a function of the temperature, pressure, and doping. In the low-temperature phases below 260 K, an incommensurate structural modulation occurs along the [110] direction which is thought to arise from the softening of a phonon mode. It is not at present clear how this phenomenon is related, if at all, to the magnetic memory effect. Here we report time-resolved measurements which track both the structural and magnetic components of the phase transition from the modulated cubic phase as it is brought into the high-symmetry phase. The results suggest that the photoinduced demagnetization modifies the Fermi surface in regions that couple strongly to the periodicity of the structural modulation through the nesting vector. The amplitude of the periodic lattice distortion, however, appears to be less affected by the demagnetization.
Time- and angle-resolved photoemission spectroscopy data of bulk terbium tritelluride (TbTe3, unidirectional charge-density-wave phase, T=100K) using a laser-based femtosecond XUV source and a hemispherical analyzer for photoelectron detection at the Fritz-Haber-Institute, Berlin, Germany. The 3D (angle, energy, pump-probe-delay) datasets include the photoemission intensities for various pump-laser fluences. The time-resolved X-ray diffraction data were obtained at the Femto hard X-ray slicing source at the Swiss Light Source, and include the charge-density-wave superlattice (2 10 1+q_CDW) peak intensities as functions of pump-probe-delay for various pump-laser fluences. The data and associated metadata are stored in the NeXus data format (https://www.nexusformat.org/).
We present a generalized multiferroic phase diagram for orthorhombic $R{\mathrm{MnO}}_{3}\phantom{\rule{4pt}{0ex}}(R=\mathrm{Gd}--\mathrm{Lu})$ based on coherently grown thin films. The magnetic order was identified by neutron-diffraction and resonant soft x-ray scattering experiments. For large $R$-ions $(R=\mathrm{Gd}--\mathrm{Dy})$, the transition temperature to a long-range ordered antiferromagnetic phase is only weakly dependent on the $R$-ion radius, but decreases monotonically with decreasing $R$-ion radius for films with $R=\mathrm{Ho}--\mathrm{Lu}$. The antiferromagnetic phase is characterized by an incommensurate order of the ${\mathrm{Mn}}^{3+}$ spins, which successively locks into a commensurate $E$-type state. These findings confirm a uniform multiferroic ground state independent of the $R$ ion and are in excellent agreement with predicted properties of strain-induced multiferroicity in these materials. In particular, strong variation of multiferroic properties in these epitaxial films compared to bulk highlights the tuning ability of strain.
Femtosecond electron diffraction data of platinum measured at the Fritz Haber Institute in Berlin. The dataset contains measurements at several absorbed energy densities, from 40 J/cm3 (experimental_data_fluence_5) to 124 J/cm3 ( experimental_data_fluence_1). The pump photon energy was 0.70 eV. The sample was a polycrystalline platinum film with a thickness of 15 nm. More information is available here: https://arxiv.org/abs/2012.10428
We investigate the demagnetization dynamics of the cycloidal and sinusoidal phases of multiferroic ${\mathrm{TbMnO}}_{3}$ by means of time-resolved resonant soft x-ray diffraction following excitation by an optical pump. The use of orthogonal linear x-ray polarizations provides information on the contribution from the different magnetic moment directions, which can be interpreted as signatures from multiferroic cycloidal spin order and sinusoidal spin order. Tracking these signatures in the time domain enables us to identify the transient magnetic phase created by intense photoexcitation of the electrons and subsequent heating of the spin system on a picosecond time scale. The transient phase is shown to exhibit mostly spin density wave character, as in the adiabatic case, while nevertheless retaining the wave vector of the cycloidal long-range order. Two different pump photon energies, 1.55 and 3.1 eV, lead to population of the conduction band predominantly via intersite $d\ensuremath{-}d$ or intrasite $p\ensuremath{-}d$ transitions, respectively. We find that the nature of the optical excitation does not play an important role in determining the dynamics of magnetic order melting. Further, we observe that the orbital reconstruction, which is induced by the spin ordering, disappears on a time scale comparable to that of the cycloidal order, attesting to a direct coupling between magnetic order and orbital reconstruction. Our observations are discussed in the context of recent theoretical models of demagnetization dynamics in strongly correlated systems, revealing the potential of this type of measurement as a benchmark for such theoretical studies.
This is the dataset for the publication on 'Advanced Materials Interfaces' with publication DOI: 10.1002/admi.202201340. The dataset contains the raw trARPES experimental data and the normalized magnetic x-ray diffraction amplitude dynamics (published in https://doi.org/10.1038/s42005-020-00407-0) of GdRh2Si2. - 'trARPES_T_20K_static_MX_cube.nxs' contains a cube of trARPES intensity along the MX cut of the surface Brillouin zone presented in Figure 1-b. - 'trARPES_T_20K_fl_(number).nxs' series contain temporal evolution of raw trARPES intensity measured at sample temperature of 20 K with pump fluence of (number) mJ/cm^2. Figure 2 a-d, 3, 4, 5 b-d, B1, C1 used these trARPES intensity evolution. - 'trARPES_T_150K_fl_(number).nxs' series contain temporal evolution of raw trARPES intensity measured at sample temperature of 150 K (above T_N) with pump fluence of (number) mJ/cm^2. Figure A1 used these trARPES intensity evolution. - 'trRXD_T_20K_fl_(number).txt' series contain temporal evolution of AF order parameter of GdRh2Si2 measured at sample temperature of 20 K with pump fluence of (number) mJ/cm^2. Figure 2-e, 4, 5 used these trRXD amplitude evolution.
Chiral multiferroic langasites have attracted attention due to their doubly chiral magnetic ground state within an enantiomorphic crystal. We report on a detailed resonant soft x-ray diffraction study of the multiferroic ${\mathrm{Ba}}_{3}{\mathrm{TaFe}}_{3}{\mathrm{Si}}_{2}{\mathrm{O}}_{14}$ at the Fe ${L}_{2,3}$ and oxygen $K$ edges. Below ${T}_{N}$ ($\ensuremath{\approx}27K$) we observe the satellite reflections $(0,0,\ensuremath{\tau}), (0,0,2\ensuremath{\tau}), (0,0,3\ensuremath{\tau})$, and $(0,0,1\ensuremath{-}3\ensuremath{\tau})$ where $\ensuremath{\tau}\ensuremath{\approx}0.140\ifmmode\pm\else\textpm\fi{}0.001$. The dependence of the scattering intensity on x-ray polarization and azimuthal angle indicate that the odd harmonics are dominated by the out-of-plane ($\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{c}}$ axis) magnetic dipole while the $(0,0,2\ensuremath{\tau})$ originates from the electron density distortions accompanying magnetic order. We observe dissimilar energy dependencies of the diffraction intensity of the purely magnetic odd-harmonic satellites at the Fe ${L}_{3}$ edge. Utilizing first-principles calculations, we show that this is a consequence of the loss of threefold crystal symmetry in the multiferroic phase.
The control of materials properties with light is a promising approach towards the realization of faster and smaller electronic devices. With phases that can be controlled via strain, pressure, chemical composition or dimensionality, nickelates are good candidates for the development of a new generation of high performance and low consumption devices. Here we analyze the photoinduced dynamics in a single crystalline NdNiO$_3$ film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally we compare our results to similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced phase transitions.
