Present and Future of the Quasi-elastic Neutron Spectroscopy at LLB. More than Simply Samples: Devices

Abstract

Cold neutrons show associated wavelength and energy of a few Å and meV. These quantities are both in tune with the atomic distances and the energies of the dynamical modes at play in condensed matter. Energy exchange resulting from an inelastic scattering process within a sample induces a significant change in the neutron's momentum. Time-of Flight (ToF) and Neutron Spin-Echo (NSE) techniques are therefore perfect spectroscopic probes to simultaneously reveal the structural and dynamical phenomena at play in a vast variety of complex systems as spin dynamics in high TC superconductors, tunneling, dynamics of quantum liquids, dynamics of soft matter, glass transition, confinement, biophysics, and local and long-range diffusion in disordered systems. Laboratoire Léon Brillouin (LLB) operates two very complementary neutron spectrometers: Mibémol, a disk-chopper ToF instrument and Muses, a Neutron Resonance Spin-Echo (NRSE) machine. Mibémol is designed to study loosely dispersive excitations in condensed matter by quasi-elastic and inelastic scattering between 0.01 and 100 meV (1 meV = 8 cm−1 = 0.25 THz). The corresponding time-scale ranges from 10−13 up to 10−10 seconds. Muses complements Mibémol for measurements of longer correlation times up to 10 ns. Experiments taking advantages of the performances of these two spectrometers make it possible to assess the broad (Q, ω) range shown in Figure 1.