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C. Dong

Publications and source records attributed to C. Dong.

At least 343 records · Page 19Linked to original sources
arXiv2004

Structure and physical properties of NaxCoO2.yH2O superconducting system

The structural properties of NaxCoO2 and NaxCoO2yH2O have been investigated. The NaxCoO2yH2O samples in general show up the superconducting transitions at around 3.5K. EDAX analyses suggest our samples have the average composition of Na0.65CoO2 for the parent compound and Na0.26CoO2yH2O for the superconducting crystals. TEM observation reveals a superstructure with wave vector q=<1/2,0, 0> in the parent Na0.65CoO2 materials. This superstructure becomes very weak in the superconducting oxyhydrates. EELS analyses show that the Co ions have the valence state of around +3.3 in the Na0.65CoO2 materials and around +3.7 in the superconducting materials.

cond-mat.supr-con↗
arXiv2003

$Fe_{0.5}Cu_{0.5}(Ba_{1-x}Sr_{x})_2YCu_2O_{7+δ}$ ($x$ = 0, 0.5 and 1) superconductors prepared by high pressure synthesis

In this paper, the $Fe$-containing superconductors $Fe_{0.5}Cu_{0.5}Ba_2YCu_2O_{7+δ}$, $Fe_{0.5}Cu_{0.5}BaSrYCu_2O_{7+δ}$ and $Fe_{0.5}Cu_{0.5}Sr_2YCu_2O_{7+δ}$ were successfully prepared by common solid-state reaction followed with a procedure of high pressure synthesis. The structural change and superconducting properties in $(Fe_xCu_{1-x})BaSrYCu_2O_{7+δ}$ ($x$ = 0 $\sim$ 1.0) systems were also investigated. Annealing experiments indicate that the occurrence of superconductivity in $Fe_{0.5}Cu_{0.5}(Ba_{1-x}Sr_{x})_2YCu_2O_{7+δ}$ ($x$ = 0, 0.5 and 1) systems is mainly induced by the procedure of high pressure synthesis, which causes the increase of oxygen content and the redistribution of $Fe$ atoms between $Cu(1)$ and $Cu(2)$ sites, but not from possible secondary phase of $YBa_2Cu_3O_{7-δ}$, $YBaSrCu_3O_{7-δ}$ or $YSr_2Cu_3O_{7-δ}$ superconductors.

cond-mat.supr-con↗
arXiv2003

Z_3 symmetry and W_3 algebra in lattice vertex operator algebras

The W_3 algebra of central charge 6/5 is realized as a subalgebra of the vertex operator algebra V_{\sqrt{2}A_2} associated with a lattice of type \sqrt{2}A_2 by using both coset construction and orbifold theory. It is proved that W_3 is rational. Its irreducible modules are classified and constructed explicitly. The characters of those irreducible modules are also computed.

math.QA↗
arXiv2002

Raman scattering, X-ray photoemission spectra and superconductivity of a tiny Ag diffusion to MgCNi3

The tiny Ag diffusion to MgCNi3 has been prepared by solid states reaction. Its structure was characterized by X-ray diffractometer (XRD). The results show that a small mount of Ag substitute for Ni sites, and much of Ag are in vacancy sites of the MgCNi3. We have further studied the surface properties of Ag-MgCNi3 using Raman scattering spectra, and X-ray photoemission spectra (XPS). Raman spectroscopy shows that the Ag-MgCNi3 has a special Raman peak around 842.1 cm-1 compared to that of C. The superconductor transition temperature (about 6.6 K) of Ag-MgCNi3 was lower than that of pure MgCNi3. It was interpreted properly by the conventional BCS phonon mechanism.

cond-mat.supr-con↗
arXiv2002

Rationality, Regularity, and C_2-cofiniteness

We demonstrate that, for CFT vertex operator algebras, C_2-cofiniteness and rationality is equivalent to regularity. In addition, we show that, for C_2-cofinite vertex operators algebras, irreducible weak modules are ordinary modules and C_2-cofinite, and V_L^+ are C_2-cofinite.

math.QA↗
arXiv2002

Superconducting properties and c-axis superstructure of Mg1-xAlxB2

The superconducting and structural properties of a series of Mg1-xAlxB2 samples have been investigated. X-ray diffraction results confirmed the existence of a structural transition associated with the significant change in inter-boron layer distance as reported previously by Slusky et al. Moreover,transmission-electron-microscopy observations revealed the existence of a superstructure with doubled lattice constant along the c-axis direction. We propose that this superstructure is essentially related to the structural transition. The modifications of superconducting transition temperature Tc, the normal state resistivity, and the upper critical field Bc2 by Al doping are discussed in terms of Al-substitution induced changes in the electronic structure at the Fermi energy.

cond-mat.supr-con↗
arXiv2002

Holomorphic Vertex Operator Algebras of Small Central Charges

We provide a rigorous mathematical foundation to the study of strongly rational, holomorphic vertex operator algebras V of central charge c = 8, 16 and 24 initiated by Schellekens. If c = 8 or 16 we show that V is isomorphic to a lattice theory corresponding to a rank c even, self-dual lattice. If c = 24 we prove, among other things, that either V is isomorphic to a lattice theory corresponding to a Niemeier lattice or the Leech lattice, or else the Lie algebra on the weight one subspace V_1 is semisimple (possibly 0) of Lie rank less than 24.

math.QA↗
arXiv2002

X-ray photoemission study of polycrystalline Mg(1-x)Al(x)B(2)

Polycrystalline Mg(1-x)Al(x)B(2) (x = 0, 0.1, 0.4, 0.5, 0.6, 1) samples have been prepared by a conventional solid state reaction. The Mg 2p, Al 2p and B 1s core level binding energies have been studied using X-ray photoemission spectroscopy (XPS). It is found that Mg 2p, Al 2p and B 1s core level binding energies increase with the Al content in Mg(1-x)Al(x)B(2) when x = 0.5, and the maxima in the binding energies of Mg 2p and Al 2p are observed in sample Mg(0.5)Al(0.5)B(2). In contrast to the Mg 2p and Al 2p core levels, the B 1s binding energy shows a minimum when x = 0.5.

cond-mat.supr-con↗
arXiv2002

Rational Vertex Operator Algebras and the Effective Central Charge

We establish that the Lie algebra of weight one states in a (strongly) rational vertex operator algebra is reductive, and that its Lie rank is bounded above by the effective central charge. We show that lattice vertex operator algebras may be characterized by the equalities of the effective central charge, the Lie rank and the central charge, and in particular holomorphic lattice theories may be characterized among all holomorphic vertex operator algebras by the equality of the Lie rank and the central charge.

math.QA↗
arXiv2001

Electron-electron interaction in multiwall carbon nanotubes

Magnetic susceptibility $χ$ of pristine and brominated arc-produced sample of multiwall carbon nanotubes was measured from 4.2 to 400 K. An additional contribution $Δχ(T)$ to diamagnetic susceptibility $χ(T)$ of carbon nanotubes was found at T $<$ 50 K for both samples. It is shown that $Δχ(T)$ are dominated by quantum correction to $χ$ for interaction electrons (interaction effects-IE). The IE shows a crossover from two-dimensional to three-dimensional at $B$ = 5.5 T. The effective interaction between electrons for interior layers of nanotubes are repulsion and the electron-electron interaction $λ$$_c$ was estimated to be $λ_c\sim $ 0.26.

cond-mat.str-el↗
arXiv2001

Preparation and Superconductivity of a MgB2 Superconducting Tape

A MgB2 superconducting tape has been successfully prepared by a new way of boron diffusion into Mg tape. This tape superconductor has a Tc of 39 K with a sharp transition width of 0.4 K, high bulk critical current density jc of 6.7*10^5 A/cm^2 in zero field at 6 K, higher irreversibility line comparing to that of a high pressure synthesized bulk sample and very small crystalline grain with size in the scale of 10-200 nm.

cond-mat.supr-con↗
arXiv2001

Superconductivity and Aluminum Ordering in Mg1-xAlxB2

Superconductivity and structural properties of Mg1-xAlxB2 materials have been systematically investigated. Evident modifications in both superconductivity and microstructure are identified to originate from the Al ordering along the c-axis direction. The resultant superstructure phase has an optimal composition of MgAlB4 with the superconducting transition at around 12K. Brief diagrams illustrating the superconductivity and structural features of Mg1-xAlxB2 materials along with the increase of Al concentration are presented.

cond-mat.supr-con↗
arXiv2000

Vertex operator algebras, generalized doubles and dual pairs

Let V be a simple vertex operator algebra and G a finite automorphism group. Then there is a natural right G-action on the set of all inequivalent irreducible V-modules. Let S be a finite set of inequivalent irreducible V-modules which is closed under the action of G. There is a finite dimensional semisimple associative algebra A_α(G,S) for a suitable 2-cocycle αnaturally determined by the G-action on S such that A_α(G,S) and the vertex operator algebra V^G form a dual pair on the sum of V-modules in S in the sense of Howe. In particular, every irreducible V-module is completely reducible V^G-module.

math.QA↗