Aachen 2019 – wissenschaftliches Programm
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T: Fachverband Teilchenphysik
T 33: Neutrino-Detektoren I
T 33.9: Vortrag
Dienstag, 26. März 2019, 18:00–18:15, S07
Effects of Holmium ions embedded in absorbers of ECHo detector arrays — •Andreas Reifenberger, Matthew Herbst, Clemens Velte, Federica Mantegazzini, Andreas Reiser, Andreas Fleischmann, Loredana Gastaldo, Sebastian Kempf, and Christian Enss for the ECHo collaboration — Kirchhoff Institute for Physics, Heidelberg University
We investigate dilute alloys of holmium in gold and silver in order to determine the impact of their specific heat on the performance of the microcalorimeters in the neutrino mass experiment ECHo. In particular, we focus on alloys with atomic concentrations of xHo=0.01 % – 1 % at temperatures between 10 mK and 800 mK. Due to the large total angular momentum J=8 and nuclear spin I=7/2 of holmium, the specific heat of Ag:Ho and Au:Ho depends on the detailed interplay of various interactions. This makes it unfeasible to accurately determine the specific heat of these materials numerically. Instead, we acquire the desired information through experiment, using three different experimental set-ups. The results from measurements on five holmium alloys show that the specific heat of these materials is dominated by a large Schottky anomaly with its maximum at T≈250 mK, which we attribute to hyperfine splitting and crystal field interactions. RKKY and dipole-dipole interactions between the holmium atoms cause additional, concentration-dependent effects. We discuss differences between Ag:Ho and Au:Ho, and conclude that alloys with xHo≈1% are suitable for ECHo, where detectors are operated at T≤30 mK.