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Séminaire MCBT : mardi 10 mai 2022 à 11h00

Matthias Raba (Institut Néel)

Titre : The ZETA option: a new way to probe excitation lifetimes with neutrons


Institut Néel, salle E424
Résumé : Inelastic neutron scattering is a preferred method for studying the dynamics of condensed matter systems at the atomic scale. In the physics or chemistry of condensed matter, the study of dispersive excitations such as phonons (lattice dynamics) and magnons (excitations of magnetic moments) is an important experimental data in many materials (HTC superconductors, thermoelectric systems, antiferromagnets, etc.). These dispersive excitations are traditionally studied by inelastic neutron scattering on a three-axes spectrometer (TAS), which makes it possible to determine the dispersion curves (relation (q,ω) of the excitations) but also their lifetime given by the inverse of the intrinsic width of the excitation. The accessible widths are generally of the order of 0.5 – 1 meV, which corresponds to lifetimes of a few pico-seconds. In order to measure much longer lifetimes, a new option has been developed these last fifteen years on the TAS IN22 installed at the ILL: ZETA (ZEro field for Three Axis). This option is based on the neutron resonant spin echo spectroscopy (NRSE).

In this seminar, I will present the working principle and the latest upgrades of ZETA. Now, this option is open to the ILL users and allows measurement of lifetimes of excitations up to several hundreds picoseconds, i.e. an energy resolution of the order of a micro-electronvolt (μeV), which corresponds to an improvement of 2 to 3 orders of magnitude.