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Jianbo Wang

Publications and source records attributed to Jianbo Wang.

46 records · Page 3Linked to original sources
arXiv2017

First-Principles Understanding of the Electronic Band Structure of Copper-Antimony Halide Perovskite: The Effect of Magnetic Ordering

We report the understanding of the electronic band structure of $Cs_4CuSb_2Cl_{12}$ perovskite through first-principles density-functional theory calculations. We find that the most stable state has the antiferromagnetic configuration where each $[CuCl_6]$ octahedral chain along the [010] direction is antiferromagnetic. The reasonable band structure of the compound can be obtained only if both the correct magnetic order and the improved exchange interaction of the Cu $\it{d}$ electrons are taken into account.

cond-mat.mtrl-sci↗
arXiv2017

Parity-Forbidden Transitions and Their Impacts on the Optical Absorption Properties of Lead-Free Metal Halide Perovskites and Double Perovskites

Using density-functional theory calculations, we analyze the optical absorption properties of lead (Pb)-free metal halide perovskites (AB$^{2+}$X$_3$) and double perovskites (AB$^+$B$^{3+}$X$_6$) (A = Cs or monovalent organic ion, B$^{2+}$ = non-Pb divalent metal, B$^+$ = monovalent metal, B$^{3+}$ = trivalent metal, X = halogen). We show that, if B$^{2+}$ is not Sn or Ge, Pb-free metal halide perovskites exhibit poor optical absorptions because of their indirect bandgap nature. Among the nine possible types of Pb-free metal halide double perovskites, six have direct bandgaps. Of these six types, four show inversion symmetry-induced parity-forbidden or weak transitions between band edges, making them not ideal for thin-film solar cell application. Only one type of Pb-free double perovskite shows optical absorption and electronic properties suitable for solar cell applications, namely those with B$^+$ = In, Tl and B$^{3+}$ = Sb, Bi. Our results provide important insights for designing new metal halide perovskites and double perovskites for optoelectronic applications.

cond-mat.mtrl-sci↗
arXiv2016

Test of non-Newtonian gravitational force at micrometer range

We report an experimental test of non-Newtonian gravitational forces at mi- crometer range. To experimentally subtract off the Casimir force and the electrostatic force background, differential force measurements were performed by sensing the lateral force between a gold sphere and a density modulated source mass using a soft cantilever. The current sensitivity is limited by the patch electrostatic force, which is further improved by two dimensional (2D) force mapping. The preliminary result sets a model independent constraint on the Yukawa type force at this range.

gr-qc↗
arXiv2016

General planar transverse domain walls realized by optimized transverse magnetic field pulses in magnetic biaxial nanowires

We report the realization of a planar transverse domain wall (TDW) with arbitrary tilting angle in a magnetic biaxial nanowire under a transverse magnetic field (TMF) pulse with fixed strength and optimized orientation profile. We smooth any twisting in azimuthal angle plane of a TDW and thus completely decouple the polar and azimuthal degrees of freedom. The analytical differential equation that describes the polar angle distribution is then derived and the resulting solution is not a Walker-ansatz form. With this optimized TMF pulse comoving, the field-driven dynamics of the planar TDW is investigated. It turns out the comoving TMF pulse increases the wall velocity under the same axial driving field. These results will help to design a series of modern logic and memory nanodevices based on general planar TDWs.

cond-mat.mes-hall↗
arXiv2014

Moduli spaces of 6 and 7-dimensional complete intersections

This paper proves the existence of homeomorphic (diffeomorphic) complex 6-dimensional (7-dim) complete intersections that belong to components of the moduli space of different dimensions. These results are given as a supplement to earlier result on 5-dimensional complete intersections.

math.AT↗
arXiv2014

The stable homotopy groups of $2$-stage Postnikov systems

The purpose of this note is to give a description of the stable homotopy group of some $2$-stage Postnikov systems for a range of dimensions. The considered $2$-stage Postnikov systems has the (weak) homotopy type of a generalized Eilenberg-Mac lane space, then their stable homotopy groups can be calculated by the stable homotopy groups of generalized Eilenberg-Mac lane spaces.

math.AT↗
arXiv2013

Remarks on 5-dimensional complete intersections

This paper will give some examples of diffeomorphic complex 5-dimensional complete intersections and remarks on these examples. Then a result on the existence of diffeomorphic complete intersections that belong to components of the moduli space of different dimensions will be given as a supplement to the results of P.Brückmann (J. reine angew. Math. 476 (1996), 209-215; 525 (2000), 213-217).

math.AT↗
arXiv2011

Comparative study of microwave absorption in Ni/SiO2 and SiO2/Ni core-shell structures

Ni coated SiO2 and SiO2 coated Ni composite particles with core-shell structures were designed, prepared and their microwave absorption properties were characterized. The comparison study of the shell effect on the effective electromagnetic parameters reveals that the effective permittivity/permeability was crucially determined by the percent and the intrinsic electromagnetic parameters of the component materials regardless of various core/shell structures. Both of the composite core-shell structures could have good microwave absorption properties. Investigation of the input impedance indicates that, good microwave absorption performances are a consequence of proper electromagnetic impedance matches when the effective electromagnetic parameters were modulated.

cond-mat.mtrl-sci↗
arXiv2011

Effect of Zn substitution on morphology and magnetic properties of copper ferrite nanofibers

Spinel ferrite Cu1-xZnxFe2O4 nanofibers over a compositional range 0 < x < 1 were prepared by electrospinning combined with sol-gel method. The influence of Zn2+ ions substitution on morphology, structure, and magnetic properties of copper ferrite has been investigated. The results show that surface of CuFe2O4 nanofibers consists of small open porosity, while surface of doped nanofibers reveals smooth and densified nature. With increasing Zn substitution, saturation magnetization initially increases and then decreases with a maximum value of 58.4 emu/g at x = 0.4, coercivity and square ratio all decrease. The influence of substitution on magnetic properties is related with the cation distraction and exchange interactions between spinel lattices.

cond-mat.mtrl-sci↗