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Now showing items 1 - 6 of 6

  • The electronic structure and magnetism of a new layered iron selenide superconductor: LiOHFeSe

    Guangtao Wang   Xia Yi   Xianbiao Shi  

    Highlights • Study the electronic and magnetic properties of LiOHFeSe. • Find the Fermi surfaces nesting induced spin density wave. • Explain the superconductivity in Li 0.8 Fe 0.2 OHFeSe, and predict the superconductivity in Li 1 − x OHFeSe. Abstract We studied the electronic structure and magnetic properties of LiOHFeSe with first-principle calculations. The strong Fermi-surface nesting in the nonmagnetic state induces magnetic instability and the spin-density-wave state, which is more stable than the other states. The calculated bare susceptibility χ 0 ( q ) peaked at the M-point and it was obviously suppressed with increasing electron and hole doping.
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  • The electronic structure and magnetism of CaFeAs<sub>2</sub>: First principles calculations

    Guangtao Wang   Xianbiao Shi   Lin Zhang   Xia Yi  

    Abstract The electronic structure, magnetism and Fermi surface (FS) nesting of the recently discovered superconductive parent material CaFeAs 2 are studied by the first-principles, based on the GGA and GGA+U methods. In the nonmagnetic state, the density of states at the Fermi level are mostly derived from the dxy , dyz and dzx orbits, just like LaOFeAs. The Fermi surfaces consist of four hole like FS sheets around the Γ -point, two electron like sheets near the Brillouin zone corner M-point, and small pockets near X-point. The hole like Fermi surfaces will strongly overlap with the electron like FS sheets, if they are shifted by the q-vector q=( π , π , 0). Such FS nesting will induce the magnetic instability and spin density wave (SDW), which has been confirmed to be more stable than other states by the calculated total energy. The calculated bare susceptibility χ 0 (q) peaked at M-point, and was obviously suppressed with the electron doping. This explains the emergence of the superconductivity in the electron-doped compound Ca 1 − x Lax FeAs 2 , because the electron doping suppressed the SDW and induced the superconductivity. Highlights • We studied the electronic structure and magnetism of CaFeAs 2 . • Studied the Fermi surface nesting at different electron and hole-doping. • We calculated the bare susceptibility and found it is different with LaOFeAs.
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  • Integrated analysis of long noncoding RNA interactions reveals the potential role in progression of human papillary thyroid cancer

    Xin You   Yixin Zhao   Jing Sui   Xianbiao Shi   Yulu Sun   Jiahan Xu   Geyu Liang   Qingxiang Xu   Yongzhong Yao  

    Recent scientific evidence has suggested that long noncoding RNAs (lncRNAs) play an important part in tumorigenesis as an important member of competing endogenous RNAs (ceRNAs). Hundreds of RNA sequence data and relevant clinic information are freely accessible in The Cancer Genome Atlas (TCGA) datasets. However, the role of cancer‐related lncRNAs in papillary thyroid cancer (PTC) is not fully understood yet. In this study, we identified 461 RNA sequencing data from TCGA. Subsequently, 45 lncRNAs, 21 miRNAs, and 78 mRNAs were chosen to construct a ceRNA network of PTC. Then, we analyzed the correlation between these 45 PTC‐specific lncRNAs and clinic features and patient outcome. Thirty‐seven of these lncRNAs were found to be closely related to age, race, gender, lymph node metastasis, TNM staging system, and patient outcome. Additionally, three of them were linked to PTC patient overall survival. Eventually, we selected eight lncRNAs randomly and performed quantificational real‐time polymerase chain reaction (qRT‐PCR) in 28 newly diagnosed patients with PTC to verify the reliability of the above results. The results of qRT‐PCR are totally in agreement with the bioinformatics analysis. Additionally, it was found that HAND2‐AS1 was negatively related to tumor size (P < 0.05). The results were consistent with the bioinformatics analysis in TCGA. Taken together, we identified the differentially expressed lncRNAs and constructed a PTC ceRNA network. The study provides a new perspective and supplement for our understanding of lncRNAs in PTC development and reveals potential diagnostic and prognostic markers in PTC.
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  • Electronic structures and magnetism of YM2Ge2 (M = Mn–Cu): Ge-hight dependent magnetic ordering in YFe2Ge2

    Guangtao Wang   Xianbiao Shi  

    Graphical abstract Highlights • Structural, electronic, and magnetic properties of YM 2 Ge 2 (M = Mn–Cu) family has been studied. • The magnetic phase diagram of YM 2 Ge 2 (M = Mn–Cu) was presented. • The electronic structure of YCo 2 Ge 2 , YNi 2 Ge 2 , and YCu 2 Ge 2 were studied for the first time. • Found Ge-hight dependent magnetic ordering in YFe 2 Ge 2 . • Two unique quantum critical point (QCP) were find in YFe 2 Ge 2 . Abstract Structural, electronic and magnetic properties of YM 2 Ge 2 (M = Mn–Cu) family are investigated by using first-principles calculations. We found that Mn and Fe compounds display antiferromagnetic ground state, while all others compounds (YCo 2 Ge 2 , YNi 2 Ge 2 , and YCu 2 Ge 2 ) favor nonmagnetic state. The magnetic order of YFe 2 Ge 2 is the stripe antiferromagnetic in the a – b plane and antiparallelly stacked along the c -axis direction. The stability of magnetic phases is very sensitive to the height of anion from the Fe plane. The ground state translates from the stripe state to A-type antiferromagnetic order when anion height is smaller than a critical value. On the contrary, when anion height is larger than a critical value, ferromagnetic ground state is favored.
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  • Electronic structures and magnetism of LaFe<sub>2</sub>Ge<sub>2</sub> and LaFe<sub>2</sub>Si<sub>2</sub>: First-principles studies

    Guangtao Wang   Xianbiao Shi  

    Highlights • Study the electronic and magnetic properties of LaFe 2 Ge 2 and LaFe 2 Si 2 . • Find LaFe 2 Ge 2 and LaFe 2 Si 2 share similar electronic structures and magnetism properties. • The band structure and Fermi surfaces exhibit significantly three dimensional character and very similar in shape to that of YFe 2 Ge 2 . • Both LaFe 2 Ge 2 and LaFe 2 Si 2 were suggested nearness to a magnetic quantum critical point (QCP). Abstract Inspired by the recent discovery of superconductivity in YFe 2 Ge 2 , we report first-principles calculations on the electronic structure and magnetic properties of LaFe 2 Ge 2 and LaFe 2 Si 2 . We found that LaFe 2 Ge 2 and LaFe 2 Si 2 share similar electronic structure and magnetism properties. In the nonmagnetic state, the density of states at the Fermi level are mostly derived from the dxy , dyz , and dzx orbits, just like the Fe-pnictide superconductors. The band structure and Fermi surfaces exhibit significantly three dimensional character. Our calculations indicate that the ground state of LaFe 2 Ge 2 and LaFe 2 Si 2 is the stripe antiferromagnetic configuration in the a-b plane and stacked antiparallel along the c-axis direction. The overestimate magnetic tendency within calculation indicates these systems nearness to a magnetic quantum critical point (QCP).
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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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