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The newly discovered ternary chalcogenide superconductor Bi2Rh3Se2has attracted growing attention, which provides an opportunity to explore the interplay between charge density wave (CDW) order and superconductivity. However, whether the phase transition around 240 K can be attributed to the formation of CDW remains controversial. To help resolve the debate, we study the electronic structure of Bi2Rh3Se2by angle-resolved photoemission spectroscopy, focusing on the nature of its high-temperature phase transition around 240 K. Our measurements demonstrate that the phase transition at 240 K is a second-order CDW phase transition. Our results reveal (i) a 2 × 2 CDW order in Bi2Rh3Se2, accompanied by the reconstruction of electronic structure, such as band folding, band splitting, and opening of CDW gaps at and away from the Fermi level; (ii) the existence of electron-boson coupling, which is manifested as an apparent kink and peak-dip-hump structure in dispersion. Our observations thus enable us to shed light on the nature of CDW order and superconductivity in Bi2Rh3Se2.

We use ultrafast optical spectroscopy to study the nonequilibrium quasiparticle relaxation dynamics of the iron-based superconductor KCa2Fe4As4F2with Tc= 33.5 K. Our results reveal a possible pseudogap (ΔPG= (2.4 ± 0.1) meV) below T* ≈ 50 K but prior to the opening of a superconducting gap (ΔSC(0) ≈ (4.3 ± 0.1) meV). Measurements under high pump fluence reveal two distinct, coherent phonon oscillations with 1.95 and 5.51 THz frequencies, respectively. The high-frequency A1g(2) mode corresponds to the c-axis polarized vibrations of FeAs planes with a nominal electron-phonon coupling constant λA1g(2)=0.194±0.02. Our findings suggest that the pseudogap is likely a precursor of superconductivity, and the electron-phonon coupling may play an essential role in the superconducting pairing in KCa2Fe4As4F2.

An emended diagnosis of the extinct cupressoid genus Ditaxocladus S. X. Guo & Z. H. Sun (syn. Fokieniopsis McIver & Basinger) and its three species is proposed based on new collections from the type locality in the Paleocene Wulonggu Formation of Altai in NW China, and other sites from China, SE Russia and western North America. Ditaxocladus planiphyllus S. X. Guo & Z. H. Sun (generitype) is now known from compound racemose fertile branches bearing several opposite pairs of globose to sub-globose seed cones composed of 6–12 decussate peltate scales, in addition to typically oppositely branched sprays. Besides D. planiphyllus, two more species are recognized based on differences in seed cone morphology. D. kivdensis Kodrul in Krassilov et al. from the Paleocene of Raichikha in Amur Province, Russia, is distinguished by similar but slender and pendulous cones, while D. catenulatus (W. A. Bell) S. X. Guo, Kvacek, Manchester & Z. K. Zhou comb. n. (syn. Fokieniopsis catenulata (W. A. Bell) McIver & Basinger and Fokienia ravenscragensis McIver & Basinger) typified by early Paleocene records in North America bears ovoid seed cones with a higher number of cone scales. All three species share the same type of bipinnately and oppositely ramified elongate sprays of cladode-like foliage and pinnately and oppositely arranged seed cones at successive nodes on compound racemose fertile branches. They differ from the living Fokienia, with which they were formerly compared, in oppositely (vs. alternately) branched leafy sprays and oppositely clustered (vs. solitary) seed cones consisting of much fewer cone scales (6–12 vs. 12–18 in Fokienia). Sterile foliage attributed to Ditaxocladus occurs in the Upper Cretaceous to Paleocene of North America, Russia and Paleocene of Spitsbergen. Tracing differentiation of Ditaxocladus populations (or species) over the Northern Hemisphere is hampered by incompleteness of most records based on quite uniform foliage without seed cones. Tetraclinis salicornioides (Unger) Kvacek from the Eocene to Pliocene of Europe and the Oligocene to Miocene of North America, which shares very similar gross morphology of foliage, differs from Ditaxocladus in the quadrivalvate seed cones and papillate leaf epidermis with undulate anticlinal walls.

An emended diagnosis of the extinct cupressoid genus Ditaxocladus S. X. Guo & Z. H. Sun (syn. Fokieniopsis McIver & Basinger) and its three species is proposed based on new collections from the type locality in the Paleocene Wulonggu Formation of Altai in NW China, and other sites from China, SE Russia and western North America. Ditaxocladus planiphyllus S. X. Guo & Z. H. Sun (generitype) is now known from compound racemose fertile branches bearing several opposite pairs of globose to sub-globose seed cones composed of 6–12 decussate peltate scales, in addition to typically oppositely branched sprays. Besides D. planiphyllus, two more species are recognized based on differences in seed cone morphology. D. kivdensis Kodrul in Krassilov et al. from the Paleocene of Raichikha in Amur Province, Russia, is distinguished by similar but slender and pendulous cones, while D. catenulatus (W. A. Bell) S. X. Guo, Kvacek, Manchester & Z. K. Zhou comb. n. (syn. Fokieniopsis catenulata (W. A. Bell) McIver & Basinger and Fokienia ravenscragensis McIver & Basinger) typified by early Paleocene records in North America bears ovoid seed cones with a higher number of cone scales. All three species share the same type of bipinnately and oppositely ramified elongate sprays of cladode-like foliage and pinnately and oppositely arranged seed cones at successive nodes on compound racemose fertile branches. They differ from the living Fokienia, with which they were formerly compared, in oppositely (vs. alternately) branched leafy sprays and oppositely clustered (vs. solitary) seed cones consisting of much fewer cone scales (6–12 vs. 12–18 in Fokienia). Sterile foliage attributed to Ditaxocladus occurs in the Upper Cretaceous to Paleocene of North America, Russia and Paleocene of Spitsbergen. Tracing differentiation of Ditaxocladus populations (or species) over the Northern Hemisphere is hampered by incompleteness of most records based on quite uniform foliage without seed cones. Tetraclinis salicornioides (Unger) Kvacek from the Eocene to Pliocene of Europe and the Oligocene to Miocene of North America, which shares very similar gross morphology of foliage, differs from Ditaxocladus in the quadrivalvate seed cones and papillate leaf epidermis with undulate anticlinal walls.

A fossil with Gnetumaffinity was found in the Jianshangou Member (Barremian Age) of the Yixian Formation (Lower Cretaceous Epoch) of the Jehol Group in western Liaoning, northeastern China. The single fossil specimen is represented by both elongate-cylindrical male spike strobiles which borne within a nodal bract of cauliflorous branch. The spike strobiles have apparent nodes, invisible internodes, and numerous verticillate involucral collars. The microsporangiate units within involucral collars are not seen. The male spike strobiles with verticillate involucral collars occur exclusively in Gnetum; hence, the fossil strobiles are attributed to a new taxon, Khitania columnispicatagen. & sp. nov., being closely related to Gnetum.The general isotopic dating suggests an age of Barremian, ca. 125–122 million years (Myr) ago for the Jianshangou Member. The palaeoecological and palaeoclimatic inference based on the compositions of flora and fauna, and lithological characters of the fossil locality suggests that the fossil plants grew in a subtropical mesophytic forest and under a warmer climate. The remains of male spike strobiles are the first record of gnetalean macrofossil. It documents the evolution of the distinct gnetoid morphology and indicates a wider range of distribution of Gnetaceae in the Early Cretaceous than present day.