Specific Heat of Holmium in Gold and Silver at Low Temperatures
Matthew Herbst, Andreas Reifenberger, Clemens Velte, Holger Dorrer, Christoph E. Düllmann, Christian Enss, Andreas Fleischmann, Loredana Gastaldo, Sebastian Kem… 展开作者
Matthew Herbst, Andreas Reifenberger, Clemens Velte, Holger Dorrer, Christoph E. Düllmann, Christian Enss, Andreas Fleischmann, Loredana Gastaldo, Sebastian Kempf, Tom Kieck, Ulli Köster, Federica Mantegazzini, Klaus Wendt
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15 pages, 4 figures. Replacement with small modifications after peer-review, no change to scientific content
The specific heat of dilute alloys of holmium in gold and in silver plays a major role in the optimization of low temperature microcalorimeters with enclosed $^{163}\textrm{Ho}$, such as the ones developed for the neutrino mass experiment ECHo. We investigate alloys with atomic concentrations of $x_\textrm{Ho}=0.01\,\% - 4\,\%$ at temperatures between $10\,\textrm{mK}$ and $800\,\textrm{mK}$. Due to the large total angular momentum $J=8$ and nuclear spin $I=7/2$ of $\textrm{Ho}^{3+}$ ions, the specific heat of $\underline{\textrm{Au}}\textrm{:Ho}$ and $\underline{\textrm{Ag}}\textrm{:Ho}$ depends on the detailed interplay of various interactions, including contributions from the localized 4f electrons and nuclear contributions via hyperfine splitting. This makes it difficult to accurately determine the specific heat of these materials numerically. Instead, we measure their specific heat by using three experimental set-ups optimized for different concentration and temperature ranges. The results from measurements on six holmium alloys demonstrate that the specific heat of these materials is dominated by a large Schottky anomaly with its maximum at $T\approx 250\,\textrm{mK}$, which we attribute to hyperfine splitting and crystal field interactions. RKKY and dipole-dipole interactions between the holmium atoms cause additional, concentration-dependent effects. With regard to ECHo, we conclude that for typical operating temperatures of $T\leq 20\,\textrm{mK}$, silver holmium alloys with $x_\textrm{Ho}\gtrsim 1\,\%$ are suited best.
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Universidad Carlos III de Madrid（马德里卡洛斯三世大学）；IMDEA Materials Institute（IMDEA材料研究所）；Institute of Mathematics, Polish Academy of Sciences（波兰科学院数学研究所）；Faculty of Mechanical Engineering, Technion-Israel Institute of Technology（以色列理工学院机械工程学院）
