TBR2 coordinates neurogenesis expansion and precise microcircuit organization via Protocadherin 19 in the mammalian cortex.

Cerebral cortex expansion is a hallmark of mammalian brain evolution; yet, how increased neurogenesis is coordinated with structural and functional development remains largely unclear. The T-box protein TBR2/EOMES is preferentially enriched in intermediate progenitors and supports cortical neurogenesis expansion. Here we show that TBR2 regulates fine-scale spatial and circuit organization of excitatory neurons in addition to enhancing neurogenesis in the mouse cortex. TBR2 removal leads to a significant reduction in neuronal, but not glial, output of individual radial glial progenitors as revealed by mosaic analysis with double markers. Moreover, in the absence of TBR2, clonally related excitatory neurons become more laterally dispersed and their preferential synapse development is impaired. Interestingly, TBR2 directly regulates the expression of Protocadherin 19 (PCDH19), and simultaneous PCDH19 expression rescues neurogenesis and neuronal organization defects caused by TBR2 removal. Together, these results suggest that TBR2 coordinates neurogenesis expansion and precise microcircuit assembly via PCDH19 in the mammalian cortex

Theory for superconductivity in (Tl,K)Fex_xSe2_2 as a doped Mott insulator

Possible superconductivity in recently discovered (Tl,K)Fe$_x$Se$_2$ compounds is studied from the viewpoint of doped Mott insulator. The Mott insulating phase is examined to be preferred in the parent compound at $x=1.5$ due to the presence of Fe vacancies. Partial filling of vacancies at the Fe-sites introduces electron carriers and leads to electron doped superconductivity. By using a two-orbital Hubbard model in the strong coupling limit, we find that the s-wave pairing is more favorable at small Hund's coupling, and d$_{x^2-y^2}$ wave pairing is more favorable at large Hund's coupling.Comment: 4+ pages, 3 figures, to appear in EP

Superconductivity and Charge-density-wave-like Transition in Th2Cu4As5

We report the synthesis, crystal structure, and physical properties of a novel ternary compound, Th$_2$Cu$_4$As$_5$. The material crystallizes in a tetragonal structure with lattice parameters $a=4.0716(1)$ {\AA} and $c=24.8131(4)$ {\AA}. Its structure can be described as an alternating stacking of fluorite-type Th$_2$As$_2$ layers with antifluorite-type double-layered Cu$_4$As$_3$ slabs. The measurement of electrical resistivity, magnetic susceptibility and specific heat reveals that Th$_2$Cu$_4$As$_5$ undergoes bulk superconducting transition at 4.2 K. Moreover, all these physical quantities exhibit anomalies at 48 K, where the Hall coefficient change the sign. These findings suggest a charge-density-wave-like (CDW) transition, making Th$_2$Cu$_4$As$_5$ a rare example for studying the interplay between CDW and superconductivity.Comment: 11 pages, 6 figures, and 1 tabl

Probing the edge-related properties of atomically thin MoS2 at nanoscale

层状二维材料具有独特的物理化学性质，使其在光电器件、传感、能源和催化等领域得到了高度关注和广泛应用。二维材料在制备过程中不可避免引入结构缺陷，虽然这些缺陷尺度仅为数纳米甚至单原子，但是会极大地改变材料的结构和电子性质，从而影响其应用。化学化工学院任斌教授课题组在层状二维材料缺陷表征方面取得进展。该工作表明了TERS在原位、高空间分辨表征缺陷位的结构和电子性质方面具有独特的优势，可以进一步推广到其他二维材料，从而有效地指导缺陷设计和材料应用。 该工作通过校内外课题组紧密合作，在任斌教授、谭平恒研究员（中科院半导体研究所）和王翔博士共同指导下完成。实验部分主要由黄腾翔博士（第一作者，已毕业化学系博士生）完成，电子能带结构与光谱理论计算由谭平恒研究员课题组从鑫博士生（共同第一作者）完成，吴思思、林楷强、姚旭、何玉韩、吴江滨、包一凡、黄声超等参与了实验与讨论。【Abstract】Defects can induce drastic changes of the electronic properties of two-dimensional transition metal dichalcogenides and influence their applications. It is still a great challenge to characterize small defects and correlate their structures with properties. Here, we show that tipenhanced Raman spectroscopy (TERS) can obtain distinctly different Raman features of edge defects in atomically thin MoS2, which allows us to probe their unique electronic properties and identify defect types (e.g., armchair and zigzag edges) in ambient. We observed an edgeinduced Raman peak (396 cm−1) activated by the double resonance Raman scattering (DRRS) process and revealed electron–phonon interaction in edges. We further visualize the edge-induced band bending region by using this DRRS peak and electronic transition region using the electron density-sensitive Raman peak at 406 cm−1. The power of TERS demonstrated in MoS2 can also be extended to other 2D materials, which may guide the defect engineering for desired properties.The authors acknowledge the final supports from MOST of China (2016YFA0200601 and 2016YFA0301204), NSFC (21633005, 21790354, 21503181, 21711530704, 21621091, 11874350, 11474277, and 11434010), Natural Science Foundation of Fujian Province (2016J05046), and China Postdoctoral Science Foundation (2017M622062). 研究工作得到科技部、国家自然科学基金委员会、福建省自然科学基金和中国博士后基金资助

Evidences for pressure-induced two-phase superconductivity and mixed structures of NiTe₂ and NiTe in type-II Dirac semimetal NiTe_(2-x) (x = 0.38 ± 0.09) single crystals

Bulk NiTe₂ is a type-II Dirac semimetal with non-trivial Berry phases associated with the Dirac fermions. Theory suggests that monolayer NiTe₂ is a two-gap superconductor, whereas experimental investigation of bulk NiTe_(1.98) for pressures (P) up to 71.2 GPa do not reveal any superconductivity. Here we report experimental evidences for pressure-induced two-phase superconductivity as well as mixed structures of NiTe₂ and NiTe in Te-deficient NiTe_(2-x) (x = 0.38±0.09) single crystals. Hole-dominant multi-band superconductivity with the P3M1 hexagonal-symmetry structure of NiTe₂ appears at P ≥ 0.5 GPa, whereas electron-dominant single-band superconductivity with the P2/m monoclinic-symmetry structure of NiTe emerges at 14.5 GPa < P < 18.4 GPa. The coexistence of hexagonal and monoclinic structures and two-phase superconductivity is accompanied by a zero Hall coefficient up to ∼ 40 GPa, and the second superconducting phase prevails above 40 GPa, reaching a maximum T_c = 7.8 K and persisting up to 52.8 GPa. Our findings suggest the critical role of Te-vacancies in the occurrence of superconductivity and potentially nontrivial topological properties in NiTe_(2-x)

Laboratory observation of ion acceleration via reflection off laser-produced magnetized collisionless shocks

Fermi acceleration by collisionless shocks is believed to be the primary mechanism to produce high energy charged particles in the Universe,where charged particles gain energy successively from multiple reflections off the shock front.Here,we present the first direct experimental evidence of ion energization from reflection off a supercritical quasi perpendicular collisionless shock,an essential component of Fermi acceleration in a laser produced magnetized plasma. We observed a quasi monoenergetic ion beam with 2,4 times the shock velocity in the upstream flow using time of flight method. Our related kinetic simulations reproduced the energy gain and showed that these ions were first reflected and then accelerated mainly by the motional electric field associated with the shock. This mechanism can also explain the quasi monoenergetic fast ion component observed in the Earth's bow shock

Impurity states in antiferromagnetic Iron Arsenides

We explore theoretically impurity states in the antiferromagnetic spin-density wave state of the iron arsenide. Two types of impurity models are employed: one has only the intraband scattering while the other has both the intraband and interband scattering with the equal strength. Interestingly, the impurity bound state is revealed around the impurity site in the energy gap for both models. However, the impurity state is doubly degenerate with respect to spin for the first case; while the single impurity state is observed in either the spin-up or spin-down channel for the second one. The impurity-induced variations of the local density of states are also examined.Comment: 4 pages, 2 figure