Terahertz parametric amplification as a reporter of exciton condensate dynamics.

Condensates are a hallmark of emergence in quantum materials such as superconductors and charge density waves. Excitonic insulators are an intriguing addition to this library, exhibiting spontaneous condensation of electron-hole pairs. However, condensate observables can be obscured through parasitic coupling to the lattice. Here we employ nonlinear terahertz spectroscopy to disentangle such obscurants through measurement of the quantum dynamics. We target Ta2NiSe5, a putative room-temperature excitonic insulator in which electron-lattice coupling dominates the structural transition (Tc = 326 K), hindering identification of excitonic correlations. A pronounced increase in the terahertz reflectivity manifests following photoexcitation and exhibits a Bose-Einstein condensation-like temperature dependence well below the Tc, suggesting an approach to monitor the exciton condensate dynamics. Nonetheless, dynamic condensate-phonon coupling remains as evidenced by peaks in the enhanced reflectivity spectrum at select infrared-active phonon frequencies, indicating that parametric reflectivity enhancement arises from phonon squeezing. Our results highlight that coherent dynamics can drive parametric stimulated emission.

Three-dimensional flat bands in pyrochlore metal CaNi2.

Electronic flat-band materials host quantum states characterized by a quenched kinetic energy. These flat bands are often conducive to enhanced electron correlation effects and emergent quantum phases of matter1. Long studied in theoretical models2-4, these systems have received renewed interest after their experimental realization in van der Waals heterostructures5,6 and quasi-two-dimensional (2D) crystalline materials7,8. An outstanding experimental question is if such flat bands can be realized in three-dimensional (3D) networks, potentially enabling new materials platforms9,10 and phenomena11-13. Here we investigate the C15 Laves phase metal CaNi2, which contains a nickel pyrochlore lattice predicted at a model network level to host a doubly-degenerate, topological flat band arising from 3D destructive interference of electronic hopping14,15. Using angle-resolved photoemission spectroscopy, we observe a band with vanishing dispersion across the full 3D Brillouin zone that we identify with the pyrochlore flat band as well as two additional flat bands that we show arise from multi-orbital interference of Ni d-electrons. Furthermore, we demonstrate chemical tuning of the flat-band manifold to the Fermi level that coincides with enhanced electronic correlations and the appearance of superconductivity. Extending the notion of intrinsic band flatness from 2D to 3D, this provides a potential pathway to correlated behaviour predicted for higher-dimensional flat-band systems ranging from tunable topological15 to fractionalized phases16.

The role of species and geography in the elemental profiles of farm-raised shrimp from Indonesia.

Elemental profiling is being explored as a traceability tool in many seafood products. However, the extent that elemental profiling can be used at finer geographical scales in cultured shrimp is unknown. Additionally, few studies have included multiple species in the same discriminant models, which would be useful in applications where one species is common, and the other is not. Here, elemental profiling was used to discern the provenance of black tiger shrimp Penaeus monodon and whiteleg shrimp Litopenaeus vannamei from the regions of North Kalimantan, Sulawesi Seletan, and Aceh in Indonesia. ICP-MS was used to determine elemental concentrations of 41 elements in shrimp muscle tissue and was the basis for multivariate and univariate statistical analyses. A MANOVA showed that multivariate differences exist in regions and between species of shrimp sampled. Univariate comparisons were utilized after the significance of the MANOVA and showed that 19 of the 24 elements above detection limits had significant differences. Classification via random forest was used to access the ability to discern, region, species, and region × species group combinations. The lowest model accuracy was the region × species combinations at 78.9%, while the highest accuracy was species irrespective of geographical origin at 93.59%. Elements that were routinely important in classification included As, B, Ba, Li, Na, Rb, Se, and Zn. Elemental profiles of white leg shrimp and black tiger shrimp are varied and potentially should not be used in the same classification models. Altogether, these results suggest that elemental profiling of farmed shrimp at finer geographic scales needs refinement as a traceability tool.

Sources of variation in elemental profiles of whiteleg shrimp (Litopenaeus vannamei) and their potential effects on the accuracy of discriminant analysis.

BACKGROUND: Elemental profiling is a tool that has been proposed to improve the traceability of seafood products. Small sources of variation can affect the outcome of elemental profiling and therefore pose to lower the overall accuracy of analyses. Here, we investigate two potential sources of variation through three experiments: laboratory variation (intra-, interlaboratory variation, and tissue matrix) and tissue variation. METHODS AND RESULTS: Samples of whitleleg shrimp (Litopenaeus vannamei) were obtained from 20 farms in Ecuador and two farms in Alabama to be analyzed. In the first experiment of the study, samples from Ecuador were analyzed at three different laboratories and compared. Two out of the five elements reported were statistically different across the three laboratories (Cu and Se). In the second experiment, the effect of tissue matrix (ground vs whole tissue during acid digestion) was investigated. Altogether, five out of 29 elements analyzed were statistically different. In the third experiment, samples from two farms in Alabama were analyzed to understand the variation in element concentrations in different tissues (head on shell on (HOSO), headless shell on (HLSO), headless peeled (PLD) and headless peeled and deveined (PLDV)). Elemental concentrations varied across tissues, and patterns in elemental concentrations were site specific. The samples from the two farms were analyzed with a Random Forest classification model to site x tissue groupings with 94% accuracy. CONCLUSION: The result of this study highlights the following: 1. Consistency in laboratory analysis important in studies that involve element concentrations, as minor differences in methodology can propagate as significant differences in results. 2. In shrimp, elements are compartmentalized in different tissues and elemental profiling should consistently use the same type of tissue.

Trace element concentrations in white leg shrimp Litopenaeus vannamei from retail stores in the EU, UK, and USA and the ability to discern country of origin with classification models.

Shrimp are a globally traded aquaculture commodity that accounts for a large proportion of the monetary value of aquaculture. There are concerns among consumers about seafood labeling fraud and environmental sustainability. Therefore, the geographic origin of shrimp from retail stores was investigated with trace element profiling. 94 shrimp samples were collected from grocery stores across the USA, UK, and EU in 70 different grocery stores. The results of 24 elements are reported. Shrimp samples were from Thailand, India, Vietnam, Indonesia, and Ecuador were shown to have 15 elements that were statistically different across labeled country of origin, with Ecuador having unique post hoc group membership in 5 of the elements. Based on a classification procedure, shrimp were classified to labeled country of origin with an overall accuracy of 71.2%. Overall, the results suggest that elemental profiling could be a traceability tool for classifying samples of shrimp from retail stores.

Identification of goat milk powder by manufacturer using multiple chemical parameters.

Concentrations of multiple elements and ratios of stable isotopes of carbon and nitrogen were measured and combined to create a chemical fingerprint of production batches of goat whole milk powder (WMP) produced by different manufacturers. Our objectives were to determine whether or not differences exist in the chemical fingerprint among samples of goat WMP produced at different sites, and assess temporal changes in the chemical fingerprint in product manufactured at one site. In total, 58 samples of goat WMP were analyzed by inductively coupled plasma-mass spectrometry as well as isotope ratio mass spectrometry and a suite of 13 elements (Li, Na, Mg, K, Ca, Mn, Cu, Zn, Rb, Sr, Mo, Cs, and Ba), δ(13)C, and δ(15)N selected to create the chemical fingerprint. Differences in the chemical fingerprint of samples between sites and over time were assessed using principal components analysis and canonical analysis of principal coordinates. Differences in the chemical fingerprints of samples between production sites provided a classification success rate (leave-one-out classification) of 98.1%, providing a basis for using the approach to test the authenticity of product manufactured at a site. Within one site, the chemical fingerprint of samples produced at the beginning of the production season differed from those produced in the middle and late season, driven predominantly by lower concentrations of Na, Mg, K, Mn, and Rb, and higher concentrations of Ba and Cu. This observed temporal variability highlights the importance of obtaining samples from throughout the season to ensure a representative chemical fingerprint is obtained for goat WMP from a single manufacturing site. The reconstitution and spray drying of samples from one manufacturer by the other manufacturer enabled the relative influence of the manufacturing process on the chemical fingerprint to be examined. It was found that such reprocessing altered the chemical fingerprint, although the degree of alteration varied among samples and individual elements. The findings of this study support the use of trace elements and stable isotope ratios to test the authenticity of goat WMP, which can likely be applied to other dairy goat products. This approach could be used test to the factory of origin (and potentially batch of origin) of products in the supply chain, thus providing the ability to audit the supply chain and monitor for fraudulent activity.