Future applications of the high-flux thermal neutron spectroscopy: the ever-green case of collective excitations in liquid metals

Abstract

The European landscape of neutron sources for research applications is changing and the major European joint effort, the European Spallation Source (ESS) currently under construction in Lund (Sweden), is progressing. The high flux source ESS is designed to deliver slow neutrons with a longpulse time structure, a rather unique feature, with characteristics optimised to maximise the instrument performances and the experimental throughput. This is expected to result in unprecedented scientific capability over broad research areas. Major breakthroughs are likely to take place in the understanding of complex, strongly interacting and disordered systems, more specifically on their dynamical response. This will have an impact on the development of novel theories to cover some of the presently existing knowledge gaps and will prompt advanced applications of the investigated materials. Liquid metals are a prototypical example of complex systems extensively studied from the sixties on, now re-emerging as powerful functional materials for unconventional and broad spectrum applications. Research on liquid metal composites will benefit of the new experimental possibilities available at the ESS. We review the status of the experiments on liquid metals dynamics, focusing on a selected set of systems, and discuss the perspectives for cutting-edge experiments at the new sources.

High-frequency Collective Ionic Dynamics in Liquid Metals

“…Nowadays, liquid metals have been actively studying, because they are known as advanced functional materials for novel applications which exploit the material flexibility coupled to the high electrical conductivity such as notably transient devices, soft robotics, biomedical sensing, and health monitoring [20]. The impact of liquids Hg and Ga as adaptive sensors and Ga-based alloys as biomaterials [21] is receiving a great attention.…”

Complex dynamics in low electron density lithium ammonia solutions. Interacting modes revealed by comparing neutron and x-ray inelastic scattering

“…Therefore the model based on more than one mode, interacting with each other, is employed [4] where the combination of two basic modes, described by the amplitude operator Q Q j , were employed by assuming the same dynamic characteristics, that is energy ( hω Q j ) and self-energy [(σ j (Q, ω)], identified by a branch index j = 1 and 2. As in other investigations the self-energy was approximated by its simplest form having the correct ω dependence, that is σ j (Q, ω) = i j (Q) ω, where j (Q) depends only on Q and, in the low damping limit, is the full width at half maximum of S j j (Q, ω).…”

“…This model [4] is known to be able to provide a straightforward description of the positive dispersion and the global evolution of the measured dynamic structure factors of Fig. 3.…”

“…Since long time, it is known that liquid metals atomic dynamics shows the presence of long living collective modes in a wide wave-vector range [1][2][3][4], with simple metals showing a scalable behavior of the dispersion relation [5]. It is also found that the collective mode velocity can be almost quantitatively accounted for by means of an electron-ion plasma model where the electron screening plays a major role [6][7][8].…”