Sprecher
Beschreibung
Magnetic systems are fertile ground for the design of novel quantum and topologically non-trivial states characterized by exotic excitations. Recent examples include spin chain and square-lattice low-dimensional antiferromagnets, quantum spin liquid candidates, spin-ice compounds, and unusual spin textures. These systems are not only of fundamental interest but may also pave the way to new technologies. For example, skyrmion spin textures open new possibilities for data storage in race track memories [1] and allow for the design of electronic–skyrmionic devices [2]. Key features of the ground state and finite-temperature behavior of a magnetic system are captured by the spectrum of its excitations. All of the aforementioned systems reveal exotic excitations dissimilar to standard magnons that form narrow bands in conventional ferro- and antiferromagnets. The detection of exotic excitations is by far more challenging, as they show broad distribution in the energy and momentum space.
We present a concept for an indirect geometry crystal time-of-flight spectrometer, which we propose for the FRM-II reactor in Garching. Recently, crystal analyzer spectrometers at modern spallation sources have been proposed and are under construction [3]. The secondary spectrometers of these instruments are evolutions of the flat cone multi-analyzer for three axis spectrometers (TAS). The instruments will provide exceptional reciprocal space coverage and intensity to map out the excitation landscape in novel materials. We will discuss the benefits of such a time-of-flight primary spectrometer with a large crystal analyzer spectrometer at a continuous neutron source. The dynamical range can be very flexibly matched to the requirements of the experiment without sacrificing the neutron intensity. At the same time, the chopper system allows a quasi-continuous variation of the initial energy resolution. The neutron optic of the proposed instrument employs the novel nested mirror optics [4], which images neutrons from a bright virtual source onto the sample. The spot size of less than 1 cm x 1 cm at the virtual source allows the realization of very short neutron pulses by the choppers, while the small and well-defined spot size at the sample position provides an excellent energy resolution of the secondary spectrometer thanks to the prismatic focusing of the analyzer.
[1] Shu Y. and et al., JMMM, 568:170387, 2023.
[2] Zang X. and et al., Science Report, 5:11369, 2015.
[3] R.I. Bewley, Nucl. Instr. Meth. Phys. Res. A, 998:165077, 2021.
[4] C. Herb, O. Zimmer, R. Georgii, P. Böni., Nucl. Instr. Meth. Phys. Res. A, 1040:167154, 2022.
