Longitudinal Neutron Resonance Spin Echo Spectroscopy under Large Energy Transfers

Abstract

Longitudinal neutron resonance spin echo (LNRSE) spectroscopy offers very high energy resolution due to the self correction of the resonant spin flippers, and a wide dynamical range nominally exceeding six orders of magnitude in resolution down to sub-ps range. In this paper, the technical realisation how to achieve such low Fourier times at the spectrometer RESEDA at the MLZ Garching is described. The requirements of data collection and data analysis in the limit of very low Fourier times, notably those related to the breakdown of the spin echo approximation, are discussed. A method to infer the scattering function from the experimental data under large energy tansfers beyond the spin echo approximation is presented.

The longitudinal neutron resonant spin echo spectrometer RESEDA

“…Along with the experimental data a solid line representing an analytical calculation considering the Bloch-Siegert shift [19] is shown. The maximum polarisation after each resonant flipper is slightly damped at low frequencies, leading to a reduction of the overall contrast in the field integral subtraction region [33] where both resonant flipper coils are operated at or close to 35 kHz. The calculated curve describes the experimental data in detail, indicating the good control of the technique.…”

Topological magnon band structure of emergent Landau levels in a skyrmion lattice

“…-10 0 10 (40,47,72). At the entry of the instrument the polarization is perpendicular to the direction of flight.…”

MIEZE Neutron Spin-Echo Spectroscopy of Strongly Correlated Electron Systems

“…It supports in particular longitudinal neutron resonance spin-echo (LNRSE) in the range from below 0.001 ps to above 20 ns for λ = 10 Å 16,41) and modulation of intensity with zero-effort (MIEZE) in the range from below 0.001ps to above 10 ns for λ = 10 Å). [42][43][44] A standard 3 He detector and a 2D CASCADE detector with an active area of 20×20 cm 2 are available. The CASCADE detector is characterized by a spatial resolution of 2.4 × 2.4 mm 2 and a temporal resolution up to 100 ns .…”

“…In particular the change of value around 0.1 ns may be accurately reproduced. 42) With the current combination of coils used in the RF spin flippers the maximum frequency of 1.2 MHz is due to the capacitive stray coupling between the B 0 -and RF-coils. Use of a small superconducting solenoid in combination with the RF coil permitted to reduce the capacitive stray coupling, such that RF spin flips could be demonstrated up to 3.6 MHz, the maximum frequency accessible with the existing electronic circuits and RF generators.…”

“…To shed further insights on the data recorded at these very short spin-echo times, the full response of the spectrometer was simulated by different methods and found to be tractable and physically meaningful. 42,43) A full account of the study on Ho 2 Ti 2 O 7 including information on the interpretation at very short spin-echo times is beyond the scope of this review and will be presented elsewhere. 44)…”