Abstract
A commercially available calorimeter has been used to investigate the specific heat of a high-quality K\(_{0.71}\)Na\(_{0.29}\)Fe\(_2\)As\(_2\)single crystal. The addenda heat capacity of the calorimeter is determined in the temperature range \(0.02 \, \mathrm{K} \le T \le 0.54 \, \mathrm{K}\). The data of the K\(_{0.71}\)Na\(_{0.29}\)Fe\(_2\)As\(_2\) crystal imply the presence of a large \(T^2\) contribution to the specific heat which gives evidence of \(d\)-wave order parameter symmetry in the superconducting state. To improve the measurements, a novel design for a calorimeter with a paramagnetic temperature sensor is presented. It promises a temperature resolution of \(\Delta T \approx 0.1 \, \mathrm{\mu K}\) and an addenda heat capacity less than \(200 \, \mathrm{pJ/K}\) at \( T < 100 \, \mathrm{mK}\).
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Notes
Apiezon Products, MI Materials Ltd, Hibernia Way, Trafford Park, Manchester M32 0ZD, United Kingdom.
National Instruments Corp., 11500 N Mopac Expwy, Austin, TX 78759–3504, USA.
Hightech Development Leiden, Zeeforel 4, 2318 MP Leiden, The Netherlands.
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Acknowledgments
Valuable discussions with S. Kempf, C. Pies, and A. Reiser are gratefully acknowledged. This work was supported by the DFG through Projects KL1824/6, WU595/3-1, BU887/15-1, En299/5-1 and by the European Community Research Infrastructures under the FP7 Capacities Specific Program, MICROKELVIN project number 228464.
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Reifenberger, A., Hempel, M., Vogt, P. et al. Specific Heat of K\(_{0.71}\)Na\(_{0.29}\)Fe\(_2\)As\(_2\) at Very Low Temperatures. J Low Temp Phys 175, 755–763 (2014). https://doi.org/10.1007/s10909-014-1168-7
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DOI: https://doi.org/10.1007/s10909-014-1168-7