Defect-modified acoustic phonons in a single layer of MoS2
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| Format: | Preprint |
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2025
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| _version_ | 1866914267477835776 |
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| author | Radic, Aleksandar Liu, Boyao Rao, Akshay Lambrick, Sam |
| author_facet | Radic, Aleksandar Liu, Boyao Rao, Akshay Lambrick, Sam |
| contents | The thermal, mechanical, and electronic performance of atomically thin semiconductors is governed by their low-energy phonons, yet the impact of atomic-scale disorder on these modes remains poorly understood. Here, we report the first measurement of acoustic phonon dispersions in a quasi-freestanding monolayer semiconductor (MoS2), using helium-3 spin-echo spectroscopy. We identify a defect-driven regime change at a critical wavevector, $q_c$, marking the breakdown of continuum elastic behavior. At this length scale, the flexural mode transitions from continuum bending to defect-pinned standing waves, while the hybridized Rayleigh wave becomes vibrationally disordered in its dispersion and linewidth. We observe multiple defect-induced Van Hove singularities deep within the Brillouin zone and strongly suppressed acoustic group velocities, providing direct experimental evidence that four-phonon processes drive thermal transport in mono- and few-layer MoS2. These results offer a microscopic explanation for the anomalously low thermal conductivity widely observed in transition-metal dichalcogenides and demonstrate how atomic-scale disorder dictates energy flow in two-dimensional materials. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2503_14464 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Defect-modified acoustic phonons in a single layer of MoS2 Radic, Aleksandar Liu, Boyao Rao, Akshay Lambrick, Sam Materials Science Mesoscale and Nanoscale Physics The thermal, mechanical, and electronic performance of atomically thin semiconductors is governed by their low-energy phonons, yet the impact of atomic-scale disorder on these modes remains poorly understood. Here, we report the first measurement of acoustic phonon dispersions in a quasi-freestanding monolayer semiconductor (MoS2), using helium-3 spin-echo spectroscopy. We identify a defect-driven regime change at a critical wavevector, $q_c$, marking the breakdown of continuum elastic behavior. At this length scale, the flexural mode transitions from continuum bending to defect-pinned standing waves, while the hybridized Rayleigh wave becomes vibrationally disordered in its dispersion and linewidth. We observe multiple defect-induced Van Hove singularities deep within the Brillouin zone and strongly suppressed acoustic group velocities, providing direct experimental evidence that four-phonon processes drive thermal transport in mono- and few-layer MoS2. These results offer a microscopic explanation for the anomalously low thermal conductivity widely observed in transition-metal dichalcogenides and demonstrate how atomic-scale disorder dictates energy flow in two-dimensional materials. |
| title | Defect-modified acoustic phonons in a single layer of MoS2 |
| topic | Materials Science Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2503.14464 |