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1. Elasticity of davemaoite as a primary contributor to lower-mantle heterogeneities

   https://doi.org/10.1126/science.adx8356  

   Zhou, Wen-Yi; Hao, Ming; Su, Wenhao; Kim, Taehyun; Chen, Sibo; Shim, Sang-Heon; Zhang, Dongzhou; Nguyen, Phuong_Q H; Armstrong, Katherine; Zhang, Jin S (November 2025, Science)

   Geophysical detection of subducted mid–ocean ridge basalt (MORB) in the lower mantle is hindered by uncertainties in the elasticity of Fe,Al,Mg,Ti–bearing davemaoite, a key MORB component. Using Brillouin spectroscopy and x-ray diffraction, we determined the elasticity of a Ca_0.906(1)Fe²⁺_0.027(1)Fe³⁺_0.042(1)Mg_0.033(1)Al_0.072(1)Ti_0.020(1)Si_0.912(1)O₃davemaoite up to 113 gigapascals and 2294 K. We found that it exhibited a shear wave velocity 10 to 20% slower than end-member davemaoite, making it the slowest phase among major lower-mantle minerals. Our models show that MORB, containing 20 to 25 volume percent davemaoite, potentially contributes to large low-shear-velocity provinces (LLSVPs), whereas a cumulate layer enriched in davemaoite crystallized from basal magma ocean may comprise ultralow-velocity zones (ULVZs). Davemaoite’s ability to host incompatible and heat-producing elements possibly links LLSVPs and ULVZs to mantle plume initiation and geochemical signatures of ocean island basalts. 

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2. High‐Pressure Single‐Crystal Elasticity and Thermal Equation of State of Omphacite and Their Implications for the Seismic Properties of Eclogite in the Earth's Interior

   https://doi.org/10.1029/2018JB016964  

   Hao, Ming; Zhang, Jin S.; Pierotti, Caroline E.; Ren, Zhiyuan; Zhang, D. (March 2019, Journal of Geophysical Research: Solid Earth)

   Abstract Omphacite is a major mineral phase of eclogite, which provides the main driving force for the slab subduction into the Earth's interior. We have measured the single‐crystal elastic moduli of omphacite at high pressures for the first time up to 18 GPa at ambient temperature using Brillouin spectroscopy. A least squares fit of the velocity‐pressure data to the third‐order finite strain equation of state yieldsK_S0′ = 4.5 (3),G₀′ = 1.6 (1) withρ₀ = 3.34 (1) g/cm³,K_S0 = 123 (3) GPa, andG₀ = 74 (2) GPa. In addition, the synchrotron single‐crystal X‐ray diffraction data have been collected up to 18 GPa and 700 K. The fitting to Holland‐Powell thermal‐pressure equation of state yieldsK_T0′ = 4.6 (5) andα₀ = 2.7 (8) × 10⁻⁵ K⁻¹. Based on the obtained thermoelastic parameters of omphacite, the anisotropic seismic velocities of eclogite are modeled and compared with pyrolite between 200 and 500 km. The largest contrast between the eclogite and pyrolite in terms of seismic properties is observed between ~310 and 410 km. 

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3. Quantitative Defect Analysis in CVD‐Grown Monolayer MoS ₂ via In‐Plane Raman Vibration

   https://doi.org/10.1002/nano.202400103  

   Hossen, Moha_Feroz; Shendokar, Sachin; Khan, Md_Arifur_Rahman; Aravamudhan, Shyam (November 2024, Nano Select)

   ABSTRACT The synthesis of two‐dimensional transition metal dichalcogenide (2D‐TMD) materials gives rise to inherent defects, specifically chalcogen vacancies, due to thermodynamic equilibrium. Techniques such as chemical vapor deposition (CVD), metal‐organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), flux growth method, and mechanical exfoliation produce large‐scale, uniform 2D TMD films, either in bulk or monolayers. However, defects on the film surface impact its quality, and it is necessary to measure defect density. The phonon confinement model indicates that the first‐order Raman band frequency shift depends on defect density. Monolayer Molybdenum disulfide (MoS₂) exhibits three phonon dispersions at the Brillouin zone edge (M point): out‐of‐plane optical phonon vibration (ZO), in‐plane longitudinal optical phonon vibration (LO), and in‐plane transverse optical phonon vibration (TO). The LO and ZO modes overlap with Raman in‐plane vibration (𝐸¹_2g) and Raman out‐of‐plane vibration (𝐴_1g), respectively, causing peak broadening. In the presence of defects, the Raman 𝐸¹_2gvibration energy decreases due to a reduced restoring force constant. The Raman 𝐴_1gvibration trend is random, influenced by both restoring force constant and mass. The study introduces a quantitative defect measurement technique for CVD‐grown monolayer MoS₂using Raman 𝐸¹_2gmode, employing sequential data processing algorithms to reveal defect density on the film surface. 

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4. Brillouin spectroscopy via an atomic line monochromator

   https://doi.org/10.1364/OE.521427  

   Hutchins, Romanus; Schumacher, Justin; Frank, Eric; Ambekar, Yogeshwari_S; Zanini, Giulia; Scarcelli, Giuliano (May 2024, Optics Express)

   Brillouin spectrometers, used for characterizing material mechanical properties, traditionally employ etalons such as Fabry-Pérot interferometers and virtually imaged phased arrays (VIPA) that use spatial dispersion of the spectrum for measurement. Here, we introduce what we believe to be a novel approach to Brillouin spectroscopy using hot atomic vapors. Using laser induced circular dichroism of the rubidium D2 line in a ladder-type configuration, we developed a narrow-band monochromator for Brillouin analysis. Unlike etalon-based spectrometers, atomic line monochromators operate in free-space, facilitating Brillouin spectroscopy integration with microscopy instruments. We report the transmission and spectral resolution performances of the spectrometer and demonstrate Brillouin spectra measurements in liquids. 

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5. Self-pulsations in a microcavity Brillouin laser

   https://doi.org/10.1364/OL.440677  

   Qin, Yingchun; Ding, Shulin; Lei, Shujian; Liu, Jie; Bai, Yan; Zhang, Menghua; Li, Yuhang; Wen, Jianming; Jiang, Xiaoshun; Xiao, Min (January 2022, Optics Letters)

   We demonstrate a new, to the best of our knowledge, kind of self-pulsation in a microcavity Brillouin laser. This specific self-pulsation is generated by the interplay between the Brillouin lasing and the thermo-optic effect in an optical microcavity. Intriguingly, the self-pulsation behaviors are simultaneously present in both forward input pump and backward Brillouin lasing emission. By developing a coupled-mode theory, our numerical simulations display an excellent agreement with the experimental results. 

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