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arXiv · 2401.03377

Elastic Softening in Synthetic Diamonds

Tatsuya Yanagisawa·Ruo Hibino·Hiroyuki Hidaka·Hiroshi Amitsuka·Toshiyuki Tashima·Mitsuhiro Akatsu·Yuichi Nemoto·Sergei Zherlitsyn·Joachim Wosnitza
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Abstract

This study reveals a previously unreported phenomenon: elastic softening of synthetic diamonds at temperatures below 1 K. We present ultrasonic measurements on single-crystalline, non-irradiated synthetic diamonds--namely, type-IIa (colorless) and type-Ib (yellow) diamonds grown by high-pressure high-temperature (HPHT) synthesis, as well as type-IIa diamond grown by chemical vapor deposition (CVD). A pronounced, divergent decrease in the elastic stiffness constant $C_{44}$ was observed in all samples down to 20 mK. We attribute this softening to electric quadrupolar degrees of freedom with irreducible representation $T_2$ in diamond. The microscopic origin of this effect, however, remains unresolved. By analogy with similar behavior observed in silicon, we suggest the presence of an as-yet-unidentified, defect-derived quantum ground state with $T_1$ or $T_2$ symmetry at ppb-level concentrations in all three diamonds studied.

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Tatsuya Yanagisawa, Ruo Hibino, Hiroyuki Hidaka, Hiroshi Amitsuka, Toshiyuki Tashima, Mitsuhiro Akatsu, Yuichi Nemoto, Sergei Zherlitsyn, Joachim Wosnitza. 2024-01-07. Elastic Softening in Synthetic Diamonds. https://doi.org/10.7566/jpsj.94.073602

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