A1 Journal article (refereed)
Specific heat of thin phonon cavities at low temperature : Very high values revealed by zeptojoule calorimetry (2022)

Tavakoli, A., Lulla, K. J., Puurtinen, T., Maasilta, I., Collin, E., Saminadayar, L., & Bourgeois, O. (2022). Specific heat of thin phonon cavities at low temperature : Very high values revealed by zeptojoule calorimetry. Physical Review B, 105(22), Article 224313. https://doi.org/10.1103/PhysRevB.105.224313

JYU authors or editors

Puurtinen, Tuomas
Maasilta, Ilari

Publication details

All authors or editors: Tavakoli, Adib; Lulla, Kunal J.; Puurtinen, Tuomas; Maasilta, Ilari; Collin, Eddy; Saminadayar, Laurent; Bourgeois, Olivier

Journal or series: Physical Review B

ISSN: 2469-9950

eISSN: 2469-9969

Publication year: 2022

Publication date: 27/06/2022

Volume: 105

Issue number: 22

Article number: 224313

Publisher: American Physical Society (APS)

Publication country: United States

Publication language: English

DOI: https://doi.org/10.1103/PhysRevB.105.224313

Publication open access: Not open

Publication channel open access:

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/82599

Publication is parallel published: https://arxiv.org/abs/2206.07383

Abstract

The specific heat of phonon cavities is investigated in order to analyze the effect of phonon confinement on thermodynamic properties. The specific heat of freestanding very thin SiN membranes in the low-dimensional limit is measured down to very low temperatures (from 6 K to 50 mK). In the whole temperature range, we measured an excess specific heat orders of magnitude bigger than the typical value observed in amorphous solids. Below 1 K, a crossover in cp to a lower power law is seen, and the value of the specific heat of thinner membranes becomes larger than that of thicker ones demonstrating a significant contribution coming from the surface. We show that this high value of the specific heat cannot be explained by the sole contribution of two-dimensional phonon modes (Lamb waves). The excess specific heat, being thickness dependent, could come from tunneling two-level systems that form in low-density regions of amorphous solids located on the surfaces. We also show that the specific heat is strongly tuned by the internal stress of the membrane by orders of magnitude, giving high values, making low-stress SiN very efficient for energy storage at very low temperature.

Keywords: thin films; nanostructures; phonons; thermodynamics; calorimetry; low temperature physics