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Now showing items 1 - 11 of 11

  • Fabricating flexible wafer-size inorganic semiconductor devices

    Yuan, Yunhuan   Xie, Senpei   Ding, Chaogang   Shi, Xianbiao   Xu, Jie   Li, Kang   Zhao, Weiwei  

    Owing to their distinct electrical and optoelectronic properties, inorganic semiconductors play an increasingly important role in the field of flexible devices. However, the inherent brittleness of inorganic semiconductors seriously limits their application and durability. In this study, we demonstrate a scheme for improving the flexibility of inorganic semiconductor materials. A wafer-size film is fabricated by dropping and annealing semiconductor ink onto a piece of paper. The film can withstand 100000 bends without a significant change in resistance. This superior flexibility can be attributed to the suppression of strain localization by the substrate. In addition, the film shows considerable stability when stored in a natural environment and can remain mostly undisturbed when immersed in water for an extended time. This study proposes a method for fabricating highly reliable inorganic semiconductors, leading to their extensive application in flexible devices.
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  • Dirac fermions in the layered titanium-based oxypnictide superconductor

    Shi, Xianbiao   Chen, Li   He, Peng   Wang, Guangtao   Zheng, Gongping   Liu, Xin   Zhao, Weiwei  

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  • Pnictide-height dependent ferromagnetism in CuFeAs and CuFeSb

    Wang, Guangtao   Shi, Xianbiao   Wang, Dongyang  

    Electronic structures and magnetism properties of CuFeAs and CuFeSb are investigated by using first-principles calculations. We found that CuFeAs and CuFeSb share similar electronic structures and magnetic properties. Unlike the antiferromagnetic isostructure LiFeAs, the ground state of both compounds is ferromagnetic state driven by the Stoner ferromagnetic instability. Their ground state is very sensitive to the height of anion (As or Sb), translating from the ferromagnetic state to the stripe antiferromagnetic ordering when the anion height is smaller than a critical value. Such magnetic phase transition can be understood by the J(1)-J(2) Heisenberg model. Reducing the anion height will decrease the nearest-neighbor interaction J(1) but increase the next-nearest-neighbor interaction J(2). The competing between the anion height dependent antiferromagnetic superexchange mediated by As(Sb) and the ferromagnetic direct exchange between Fe results the variations of magnetic structure with anion height. (C) 2016 Elsevier B.V. All rights reserved.
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  • Electronic Structures and Magnetism of CaFeAsH and CaFeAsF

    Wang, Guangtao   Shi, Xianbiao   Liu, Haipeng   Liu, Qingbo  

    We studied the electronic structures, magnetism, and Fermi surface (FS) nesting of CaFeAsH and CaFeAsF by first-principles calculations. In the nonmagnetic (NM) states, we found strong FS nesting, which induces magnetic instability and a spin density wave (SDW). Our calculations indicate that the ground state of CaFeAsH and CaFeAsF is the stripe antiferromagnetic state. The calculated bare susceptibility chi 0(q) peaked at the M-point and was clearly suppressed and became slightly incommensurate with both electron doping and hole doping for both materials.
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  • Electronic Structure and Magnetism of the Multiband New Superconductor CaRbFe4As4

    Shi, Xianbiao   Wang, Guangtao  

    By first-principles calculations, we investigated the electronic structure, magnetism, and Fermi surface (FS) nesting of the newly discovered superconductor CaRbFe4As4. In the nonmagnetic (NM) state, there are ten bands crossing the Fermi level, which is more complicated than other FeAs-based superconductors, showing a multiband character. The FS consists of six holelike sheets around the Gamma-point and four electronlike sheets near the Brillouin zone corner M-point. The holelike FSs will overlap with the electronlike FS sheets, if they are shifted by the vector q =3D (pi, pi, 0). Such FS nesting induces the bare susceptibility peak chi(0)(q) at the M-point. Fixed spin moment calculations indicate that CaRbFe4As4 has a strong tendency towards magnetism. Total energy calculations predicted that the ground state of CaRbFe4As4 is the stripe antiferromagnetic state. Therefore, CaRbFe4As4 is strongly similar to other FeAs-based superconductors, although it crystallized with a unique crystal structure.
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  • The de Hass-van Alphen quantum oscillations in a three-dimensional Dirac semimetal TiSb2

    Xia, Wei   Shi, Xianbiao   Wang, Yushu   Ge, Wenna   Su, Hao   Wang, Qin   Wang, Xia   Yu, Na   Zou, Zhiqiang   Hao, Yufeng   Zhao, Weiwei   Guo, Yanfeng  

    Characterization of the Fermi surface of high-quality crystalline TiSb2 by de Hass-van Alphen measurement reveals nontrivial topological properties. Moreover, our analysis of the quantum oscillation frequencies associated with nonzero Berry phase when the magnetic field is parallel to both the ab-plane and c-axis of TiSb2 finds that the Fermi surface topology has a three-dimensional feature. The results are supported by first-principle calculations which reveal a symmetry-protected Dirac point along the Gamma-Z high symmetry line near the Fermi level. On the (001) surface, the bulk Dirac points are found to project onto the point with nontrivial surface states. Our finding will substantially enrich the family of 3D Dirac semimetals which are useful for topological applications.
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  • Electronic structure and optical properties of Cs(2)AX(2)' X-4 (A=3DGe,Sn,Pb; X,' X=3DCl,Br,I)

    Wang, Guangtao   Wang, Dongyang   Shi, Xianbiao  

    We studied the crystal structures, electronic structures and optical properties of Cs(2)AX(2)'X-4 (A=3DGe, Sn, Pb; X', X=3DCl, Br, I) compounds using the first-principles calculation. Our optimized structures agree well with experimental and theoretical results. Band structure calculations, using the modified Becke-Johnson (mBJ) potential method, indicate that these compounds (with the exception of Cs2PbX2'I-4) are semiconductors with the direct band gap ranging from 0.36 to 4.09 eV. We found the compounds Cs2GeBr2I4, Cs2GeCl2I4, Cs2GeI2Br4, Cs2SnI6, and Cs2SnBr2I4 may be good candidates for lead-free solar energy absorber materials. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
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  • Broken cubic symmetry driven co-emergence of type-I and type-II Dirac points in topological crystalline insulator ThTaN3

    Tian, Xin   Shi, Xianbiao   He, Peng   Yang, Hongxin   Zhao, Weiwei   Wang, Guang-Tao  

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  • Overexpression of Long Noncoding RNA PTENP1 Inhibits Cell Proliferation and Migration via Suppression of miR-19b in Breast Cancer Cells

    Shi, Xianbiao   Tang, Xiaoqiao   Su, Lei  

    This study aimed to investigate the effect of long noncoding RNA PTENP1 in the development of breast cancer (BC). Quantitative real-time PCR was utilized to determine the expression of PTENP1 in tissues and cell lines. pcDNA3.1 and shRNA were used to over- and low-express PTENP1 in BC cell lines, and miR-19b mimic and inhibitor were utilized to over- and low-express miR-19b. Then the abilities of cell survival, apoptosis, migration, and invasion were assessed in BC cells with different expression levels of PTENP1 and miR-19b. The expression of PTENP1 was significantly downregulated in both BC tissues and cell lines. Overexpressed PTENP1 could significantly increase cell survival, colony forming, migration, and invasion but decrease apoptosis in BC cell lines. However, overexpressed miR-19b performed contrary effects compared with PTENP1 on cell survival, colony forming, migration, invasion, and apoptosis in BC cell lines. miR-19b can be downregulated by PTENP1, and the effect of overexpressed PTENP1 on the PI3k/Akt pathway could be aborted by overexpressed miR-19b. PTENP1 performed a negative role in the development of BC via downregulating miR-19 probably through the PTEN/PI3K/Ala pathway.
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  • Electronic Structure and Magnetism of the Multiband New Superconductor CaRbFe\r 4\r As\r 4

    Shi, Xianbiao   Wang, Guangtao  

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  • Self-hole-doping–induced superconductivity in KCa2Fe4As4F2 Guangtao Wang, Zhenwei Wang and Xianbiao Shi Interaction of superconductivity and magnetism in borocarbide superconductors K-H Müller and V N Narozhnyi Spiral magnetism in the single-band Hubbard model: the Hartree–Fock and slave-boson approaches

    Wen Fong Goh   Warren E. Pickett  

    Unlike the other prominent macroscopic spin-paired quantum state, superconductivity, where the focus is on the strongest coupling within a class, untuned weak magnetism presents an intellectual frontier where electronic structure, magnetic coupling, and (quantum and thermal) fluctuations provide a platform for unconventional phenomena. With a strong van Hove singularity (vHs) at the Fermi energy, TiAu (with no magnetic element) is highly unstable toward ferromagnetism, yet orders antiferromagnetically at a wave vector unrelated to Fermi surface nesting. We show that mirrored vHs provide the long-wavelength, low-frequency fluctuations characteristic of a wFM rather than that of a conventional wAFM, whereby wAFM competes on equal terms with wFM for the broken symmetry ordered state. Peierls-like energy gain from cell doubling can help promote wAFM, which is evident in TiAu. Copyright c © EPLA, 2016 Background. – Weak itinerant ferromagnets (wFMs), conventionally understood as stoichiometric compounds comprised of elements not displaying local moments themselves, are few, and command attention for that reason as well as for their existence at the extreme. Their sister weak anti ferromagnetic systems (wAFM) are practically nonexistent, making the recent identification [1] of the wAFM TiAu a phenomenon in need of understanding. wFM phenomena and materials, reviewed recently [2], provide one of the main platforms to study quantum-critical points, where ordered phases (most often magnetic) appear or vanish at second order, or weakly first-order, phase transitions, accessed by tuning such as by doping or pressure. These long-wavelength (wave vector q → 0) processes are displayed in an assortment of materials [2], with some of the prominent examples being understood in terms of the Stoner instability of the nonmagnetic phase [3,4]. In terms of the magnetic exchange coupling I of states at the Fermi surface (FS), and the Fermi level (EF ) density of states N(EF ), if IN(EF ) > 1 the itinerant system can sacrifice increased kinetic energy by a gain in exchange (magnetic) energy, and ferromagnetism – possibly weak – becomes the stable phase. The theory of such phases including the quantum-critical and thermal fluctuations attending the small order parameter, is well developed by Moriya and collaborators [5–8], Hertz [9], Millis [10], and several others since [2,11]. We address here not critical phenomena but rather the underlying origin of the electronic instability. Moriya’s self-consistent renormalization (SCR) theory of spin fluctuations [7] provides a useful guide for our purposes, as it ties the small ω, small q ≡ | q | (for wave vectors Q; q near the ordering wave vector Q ) behavior to averages of various Fermi surface quantities, thus bringing the focus to the geometry, topology, velocity, and effective mass fields of the FS. wAFMs, and their spin density wave (SDW) cousins, have been discussed theoretically almost exclusively in terms of FS nesting [12,13], and the SDW cases generally support that mechanism. TiAu, however, appears to present its strongest nesting [1] at an incommensurate wave vector that is well separated from what is observed. An added conundrum is that the Fermi energy in TiAu lies almost exactly on a sharp, narrow van Hove singularity (vHs) peak in N(E) that implies a Stoner instability, in which case ferromagnetism or possibly superconductivity, rather than wAFM, is expected to emerge. We have found, however, that a re-analysis of the susceptibility accounting for mirrored vHs and techniques based on first density functional theory can resolve these conundrums, revealing an unanticipated mechanism of AFM ordering in itinerant systems. Properties of TiAu. – TiAu, space group Pmma (#51), is orthorhombic with two formula units (f.u.) per
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