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Exotic quantum solids can host electronic states that spontaneously break rotational symmetry of the electronic structure, such as electronic nematic phases and unidirectional charge density waves (CDWs). When electrons couple to the lattice, uniaxial strain can be used to anchor and control this electronic directionality. Here, we reveal an unusual impact of strain on unidirectional “smectic” CDW orders in kagome superconductors ${\mathrm{AV}}_3{\mathrm{Sb}}_5$using spectroscopic-imaging scanning tunneling microscopy. We discover local decoupling between the smectic electronic director axis and the direction of anisotropic strain. While the two can generally be aligned along the same direction in regions of a small CDW gap, the tendency for alignment decreases in regions where the CDW gap is the largest. This feature, in turn, suggests nanoscale variations in smectic susceptibility, which we attribute to a combination of local strain and electron correlation strength. Overall, we observe an unusually high decoupling rate between the smectic electronic director of the three-state Potts order and anisotropic strain, revealing weak smectoelastic coupling in the CDW phase of kagome superconductors. This finding is phenomenologically different from the extensively studied nematoelastic coupling in the Ising nematic phase of Ising nematic phase of Fe-based superconductor bulk single crystals, providing a contrasting picture of how strain can control electronic unidirectionality in different families of quantum materials. Published by the American Physical Society2025 

The echinoid genus Tetrapygus was initially described by L. Agassiz (1841) based on a single species, Tetrapygus niger Molina, 1782. Since the extensive work conducted by Mortensen (1935), Tetrapygus has received limited taxonomic attention over the past century. Recent discoveries of new fossil species of Arbacia Gray, 1835 from the upper Pliocene of northern Chile revealed striking morphological similarities between the two distinct Arbaciidae genera Arbacia and Tetrapygus. These findings compelled new investigations to evaluate the taxonomic status of these genera. Based on molecular mitochondrial (COI), nuclear (28S), and morphological evidence, Tetrapygus niger is here recovered as the sister species to Arbacia dufresnii, both species forming a clade within the phylogeny of South American species of Arbacia. Consequently, the diagnosis and description of Tetrapygus niger are here revised, and the species is reattributed to Arbacia, as previously proposed by A. Agassiz in Agassiz & Desor (1846) under the species name Arbacia nigra. An emended diagnosis of Arbacia is also proposed in light of these new findings.  

Abstract Over the past century of maize (Zea mays L.) breeding, grain yield progress has been the result of improvements in several other intrinsic physiological and morphological traits. In this study, we describe (i) the contribution of kernel weight (KW) to yield genetic gain across multiple agronomic settings and breeding programs, and (ii) the physiological bases for improvements in KW for US hybrids. A global-scale literature review concludes that rates of KW improvement in US hybrids were similar to those of other commercial breeding programs but extended over a longer period of time. There is room for a continued increase of kernel size in maize for most of the genetic materials analysed, but the trade-off between kernel number and KW poses a challenge for future yield progress. Through phenotypic characterization of Pioneer Hi-Bred ERA hybrids in the USA, we determine that improvements in KW have been predominantly related to an extended kernel-filling duration. Likewise, crop improvement has conferred on modern hybrids greater KW plasticity, expressed as a better ability to respond to changes in assimilate availability. Our analysis of past trends and current state of development helps to identify candidate targets for future improvements in maize.