Monday 18 January 2021, 13:45 CET
Time resolved SAXS studies of nanocube assembly in levitating drops

Speaker: Prof Lennart Bergström, Department of Materials and Environmental Chemistry, Stockholm University, Sweden
Host: Dr Tomás Plivelic, manager at CoSAXS beamline

Keywords: Nanoparticle assembly, Time-resolved small angle X-ray scattering (SAXS)

Nanoparticle assembly is a promising route to produce mesostructured materials with unique properties. Probing the dynamics of assembling nanoparticles in liquids is challenging and requires not only methods with suitable spatial- and time-resolution, but also careful design of measurement environments. Here, recent work on time-resolved techniques have been used to probe nanocube assembly in levitating drops. Time-resolved small angle X-ray scattering (SAXS) combined with electron microscopy and interparticle potential calculations showed that the evaporation-induced mesocrystallization process proceeds in two stages involving the formation and rapid transformation of a dense, structurally disordered phase into ordered mesocrystals (1). It will be demonstrated how evaporation-driven poor-solvent enrichment allows for the assembly of large particle assemblies, which display a higher crystalline quality compared to the classical single solvent approach (2). Evaporation-induced assembly in weak magnetic fields was found to proceed in two stages where assembly of micron-sized mesocrystals with a cubic shape preceded the formation of fibers with a high degree of crystallographic coherence and tunable diameters (3). We will discuss how the transition from 3D growth of the primary mesocrystals to the second stage 1D assembly of the elongated fibers was related to the size and field dependence of isotropic van der Waals and directional dipolar interactions between the interacting mesocrystals.

1.M Agthe, T S. Plivelic, A Labrador, L Bergström, G Salazar-Alvarez, Nano Lett., 16, 6838-6843 (2016)
2. Z-P Lv, M Kapuscinski, L Bergström, Nature Comm., 10, 4228 (2019)
3. M Kapuscinski, P Munier, M Segad, L Bergström, Nano Lett., 20, 10, 7359–7366 (2020)


Monday, 14 December 2020 at 13:45 CET
Electronically driven spin-reorientation transition of the correlated polar metal Ca3Ru2O7

Speaker: Prof Philip King, School of Physics and Astronomy, University of St. Andrews, UK
Host: Dr. Craig Polley, scientist at the BLOCH beamline

Keywords: spin-orbit coupling in solids, angle-resolved photoemission spectroscopy

The influence of spin-orbit coupling in solids has become the subject of much attention in recent years. When combined with a breaking of inversion symmetry, it can lift the spin degeneracy of electronic states via the so-called Rashba effect, with potential applications in spin-generation and manipulation, spin-transfer torques, and the formation of topological states.1 Here, using angle-resolved photoemission spectroscopy, I will demonstrate how Rashba-type spin-orbit interactions mediate a dramatic reconstruction of the Fermi surface accompanying at a spin-reorientation phase transition in the correlated polar metal Ca3Ru2O7,2 pointing to a new form of magneto-electronic coupling, and highlighting the delicate balance between symmetry-breaking, electronic correlations, and spin-orbit coupling in solids.

Manchon et al., Nature Materials 14 (2015) 871
Marković et al., PNAS 117 (2020) 15524