When: 9 December, 15:00–16.00 CET
Where: LINXS, The Loop, Rydbergs torg 4, Lund, Sweden and online via Zoom
Speaker: Mechthild Enderle, Senior Scientist at Institut Max von Laue – Paul Langevin (ILL), Grenoble, France
Title: How polarised neutrons take the fingerprint of unusual magnetic excitations
Abstract
Every solid periodic array of atoms or magnetic moments has its own characteristic excitation spectrum of lattice or magnetic motions that crucially depends on the nature of the ground state and the pattern of interactions that stabilize this ground state. Energies and amplitudes of the motion depend on the 3D direction of the propagation and the spatial period (wavelength/wavevector) of the motion's pattern. Due to the weak interaction of the neutron with matter, the intensity in inelastic neutron scattering captures directly the squared amplitudes of the motion as function of energy and wave vector. Neutron scattering is therefore an extraordinary tool for lattice and magnetic motions and their direct comparison with theory.
These motions are quantized both in energy and momentum due to the periodic nature of the spatial arrangement of the atoms or magnetic moments, but often a classical picture that attributes an amplitude to every individual atom or magnetic moment describes the motion perfectly well - we deal with the ordinary phonons and spin-wave excitations.
However, if the ground state is of "entangled" magnetic nature, a "magnetic macroscopic quantum ground state", the behaviour of an individual atom or magnetic moment is not relevant and not well-defined, neither in the ground state nor in the motion. Nevertheless neutron scattering still captures the characteristic intensity-energy-wavevector pattern of the whole entangled assembly and therefore allows invaluable insight into these ground states and their often very counter-intuitive phenomena and properties. Preparing a neutron beam with a specific neutron spin state, and analysing this state in addition to energy and momentum transfer, provides a powerful tool to access not only squared amplitudes but even the vectorial amplitude of a magnetic excitation, be it "ordinary" or of "entangled" nature. The talk shall focus on the "handedness" of the amplitude (chirality), and give examples of ordinary as well as unusual excitations, from ferromagnets over altermagnets to entangled four-spinon states.
Biography
Mechthild Enderle is senior scientist at the Institut Max von Laue - Paul Langevin (ILL) in Grenoble, France. She is responsible for a polarised thermal triple axis spectrometer, the flagship of its kind. She investigates the excitation spectra of quantum ground states in magnetic materials, and their particular features in unpolarised and polarised neutron spectroscopy. She obtained her habilitation at the university of Saarland, her PhD at the the university of Mainz, and her master at the Technical University of Karlsruhe. After a post-doc at Risø National Laboratory, Roskilde, she joined the ILL where her interest in polarisation analysis led her to develop together with the 3He-group a new wide-angle polarisation technique (PASTIS3) that allows to separate various polarised cross sections in anisotropic single crystals.
Contact: Please contact mia.lindstrom@linxs.lu.se for practical questions
During our events we sometimes take photographs and short film clips to profile our activities. Please let us know if you don’t want to be in any photos/films before we start the event. Some webinars are recorded to be used for educational purposes in the LINXS website.
By registering to our events you give your permission to LINXS, according to the General Data Protection Regulation (GDPR), to register your name and e-mail address to be used for the sole purpose of distributing newsletters and communications on LINXS activities.