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Dive into the research topics where Hangdong Wang is active.

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Featured researches published by Hangdong Wang.


EPL | 2011

Fe-based superconductivity with Tc=31 K bordering an antiferromagnetic insulator in (Tl,K) FexSe2

Minghu Fang; Hangdong Wang; Chiheng Dong; Zujuan Li; Chunmu Feng; Jian Chen; H. Q. Yuan

(Tl,K)FexSe2 single crystals were first successfully synthesized with the Bridgeman method. The physical properties are characterized by electrical resistivity, magnetic susceptibility and Hall coefficient. We found that the (Tl,K)FexSe2 (1.30 ≤ x ≤ 1.65) compounds show an antiferromagetic (AFM) insulator behavior, which may be associated with the Fe-vacancy ordering in the crystals. While in the 1.70 ≤ x < 1.78 crystals, superconductivity (SC) coexists with an insulating phase. As Fe content further increases, the bulk SC with Tc=31 K (and a Tconset as high as 40 K) appears in the 1.78 ≤ x ≤ 1.88 crystals. Our discovery represents the first Fe-based high-temperature superconductivity (HTSC) at the verge of an AFM insulator.


Nature | 2012

Re-emerging superconductivity at 48 kelvin in iron chalcogenides

Liling Sun; Xiao-Jia Chen; Jing Guo; Peiwen Gao; Qing-Zhen Huang; Hangdong Wang; Minghu Fang; Xiaolong Chen; Genfu Chen; Qi Wu; Chao Zhang; Dachun Gu; Xiaoli Dong; Lin Wang; Ke Yang; Aiguo Li; Xi Dai; Ho-kwang Mao; Zhongxian Zhao

Pressure plays an essential role in the induction1 and control2,3 of superconductivity in iron-based superconductors. Substitution of a smaller rare-earth ion for the bigger one to simulate the pressure effects has surprisingly raised the superconducting transition temperature Tc to the record high 55 K in these materials4,5. However, Tc always goes down after passing through a maximum at some pressure and the superconductivity eventually tends to disappear at sufficiently high pressures1-3. Here we show that the superconductivity can reemerge with a much higher Tc after its destruction upon compression from the ambient-condition value of around 31 K in newly discovered iron chalcogenide superconductors. We find that in the second superconducting phase the maximum Tc is as high as 48.7 K for K0.8Fe1.70Se2 and 48 K for (Tl0.6Rb0.4)Fe1.67Se2, setting the new Tc record in chalcogenide superconductors. The presence of the second superconducting phase is proposed to be related to pressure-induced quantum criticality. Our findings point to the potential route to the further achievement of high-Tc superconductivity in iron-based and other superconductors.Pressure has an essential role in the production and control of superconductivity in iron-based superconductors. Substitution of a large cation by a smaller rare-earth ion to simulate the pressure effect has raised the superconducting transition temperature Tc to a record high of 55 K in these materials. In the same way as Tc exhibits a bell-shaped curve of dependence on chemical doping, pressure-tuned Tc typically drops monotonically after passing the optimal pressure. Here we report that in the superconducting iron chalcogenides, a second superconducting phase suddenly re-emerges above 11.5 GPa, after the Tc drops from the first maximum of 32 K at 1 GPa. The Tc of the re-emerging superconducting phase is considerably higher than the first maximum, reaching 48.0–48.7 K for Tl0.6Rb0.4Fe1.67Se2, K0.8Fe1.7Se2 and K0.8Fe1.78Se2.


Physical Review Letters | 2011

Distinct Fermi Surface Topology and Nodeless Superconducting Gap in a (Tl0.58Rb0.42)Fe1.72Se2 Superconductor

Daixiang Mou; Shanyu Liu; Xiaowen Jia; Junfeng He; Yingying Peng; Lin Zhao; Li Yu; Guodong Liu; Shaolong He; Xiaoli Dong; Jun Zhang; Hangdong Wang; Chiheng Dong; Minghu Fang; Xiaoyang Wang; Qinjun Peng; Zhimin Wang; Shenjin Zhang; Feng Yang; Zuyan Xu; Chuangtian Chen; X. J. Zhou

High resolution angle-resolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the (Tl0.58Rb0.42)Fe1.72Se2 superconductor with a T(c) = 32  K. The Fermi surface topology consists of two electronlike Fermi surface sheets around the Γ point which is distinct from that in all other iron-based superconductors reported so far. The Fermi surface around the M point shows a nearly isotropic superconducting gap of ∼12  meV. The large Fermi surface near the Γ point also shows a nearly isotropic superconducting gap of ∼15  meV, while no superconducting gap opening is clearly observed for the inner tiny Fermi surface. Our observed new Fermi surface topology and its associated superconducting gap will provide key insights and constraints into the understanding of the superconductivity mechanism in iron-based superconductors.


Applied Physics Letters | 2008

On the origin of ferromagnetism in CeO2 nanocubes

Mingyuan Ge; Hangdong Wang; En-Zuo Liu; J. Liu; J. Z. Jiang; Yupeng Li; Zhu-An Xu; Haiyang Li

Magnetic behaviors of pure CeO2 nanoparticles and nanocubes have been investigated both experimentally and theoretically. It is found that monodisperse CeO2 nanocubes with an average size of 5.3 nm do show ferromagnetic behavior at ambient temperature with a saturation magnetization of about 5.7 memu/g and coercive force of about 69 Oe. First-principles calculations reveal that oxygen vacancies in pure CeO2 cause spin polarization of f electrons for Ce ions surrounding oxygen vacancies, resulting in net magnetic moment for pure CeO2 samples. One oxygen vacancy at surface can induce more magnetic moments than those induced by one oxygen vacancy in bulk. The results obtained here provide evidence that pure CeO2 sample with oxygen vacancies can indeed have magnetic behavior. This study will stimulate more investigations for understanding the origin of ferromagnetic TM-doped CeO2 (TM=3d transition metals) in a particular case and TM-doped semiconductor oxides in general at ambient temperature.


EPL | 2011

Superconductivity at 32 K and anisotropy in Tl0.58Rb0.42Fe1.72Se2 crystals

Hangdong Wang; Chiheng Dong; Zujuan Li; Qianhui Mao; Sha-Sha Zhu; Chunmu Feng; H. Q. Yuan; Minghu Fang

Tl0.58Rb0.42Fe1.72Se2 single crystals were successfully synthesized with the Bridgeman method. The physical properties are characterized by electrical resistivity, magnetization and Hall resistivity. Tl0.58Rb0.42Fe1.72Se2 undergoes a superconducting transition at Tconset=32 K and Tczero=31.4 K. Extrapolation of the upper critical field Hc2 at Tc to zero temperature gives a large value of Hc2(0) (Hc2(0)=221 T for H∥ab and Hc2(0)=44.2 T for H∥c). The Hall coefficient changes sign upon cooling down, indicating a possible multi-band behavior. The normal-state magnetic susceptibility decreases with decreasing temperature, suggesting strong antiferromagnetic (AFM) spin fluctuations, which might be related to the superconductivity (SC).


Physical Review B | 2010

Weak anisotropy of the superconducting upper critical field in Fe 1.11 Te 0.6 Se 0.4 single crystals

Minghu Fang; Jinhu Yang; Fedor Balakirev; Y. Kohama; John Singleton; B. Qian; Z. Q. Mao; Hangdong Wang; H. Q. Yuan

We have determined the resistive upper critical field Hc2 for single crystals of the superconductor Fe1.11Te0.6Se0.4 using pulsed magnetic fields of up to 60T. A rather high zero-temperature upper critical field of mu0Hc2(0) approx 47T is obtained, in spite of the relatively low superconducting transition temperature (Tc approx 14K). Moreover, Hc2 follows an unusual temperature dependence, becoming almost independent of the magnetic field orientation as the temperature T=0. We suggest that the isotropic superconductivity in Fe1.11Te0.6Se0.4 is a consequence of its three-dimensional Fermi-surface topology. An analogous result was obtained for (Ba,K)Fe2As2, indicating that all layered iron-based superconductors exhibit generic behavior that is significantly different from that of the high-Tc cuprates.


Journal of Sound and Vibration | 2003

A solution of a non-homogeneous orthotropic cylindrical shell for axisymmetric plane strain dynamic thermoelastic problems

H.J. Ding; Hangdong Wang; W.Q. Chen

A solution of a non-homogeneous orthotropic elastic cylindrical shell for axisymmetric plane strain dynamic thermoelastic problems is developed. Firstly, a new dependent variable is introduced to rewrite the governing equation, the boundary conditions as well as the initial conditions. Secondly, a special function is introduced to transform the inhomogeneous boundary conditions to the homogeneous ones. Then by virtue of the orthogonal expansion technique, the equation with respect to the time variable is derived, of which the solution can be obtained. The displacement solution is finally presented, which can degenerate in a rather straightforward way to the solution for a homogeneous orthotropic cylindrical shell and isotropic solid cylinder as well as that for a non-homogeneous isotropic cylindrical shell. Using the present method, integral transform can be avoided. It is fit for a cylindrical shell with arbitrary thickness subjected to arbitrary thermal loads. It is also very convenient to deal with dynamic thermoelastic problems for different boundary conditions. Besides, the numerical calculation involved is very easy to be performed. Several examples are presented.


Physical Review B | 2011

Revised phase diagram for the FeTe1−xSexsystem with fewer excess Fe atoms

Chiheng Dong; Hangdong Wang; Zujuan Li; Jian Chen; H. Q. Yuan; Minghu Fang

We observed bulk superconductivity in the FeTe1-xSex crystals with a low Se concentration after the excess Fe atoms existing unavoidably in crystals as-grown are partially removed by means of annealing in the air. A revised magnetism and superconductivity phase diagram is obtained via resistivity and magnetic susceptibility measurements for FeTe1-xSex system. It is found that bulk superconductivity coexists with antiferromagnetic order in the crystals with 0.05<x<0.20. The phase diagram is very similar to the case of the K-doping or Co-doping BaFe2As2, as well as of SmFeAsO1-xFx iron-pnictide system, perhaps indicating that all iron-based systems have a generic phase diagram, although antiferromagnetic wave vector in the parent compounds of these systems is remarkable different.


Journal of Applied Physics | 2010

Enhancing magnetoelectric effect via the curvature of composite cylinder

Hangdong Wang; E. Pan; W.Q. Chen

We solved analytically the magnetoelectric (ME) effect in a bilayered piezoelectric/piezomagnetic cylinder under harmonic excitation. We revealed that at a fixed thickness ratio of the layers, the static or low-frequency ME effect can be substantially enhanced by increasing the curvature of the cylinder. In the megahertz frequency domain, on the other hand, we observed that the peak ME effect can be considerably increased by decreasing the curvature. We further showed that at a fixed curvature, the ME effect can be tuned to be around the resonant frequency for giant output by varying the boundary condition and thickness ratio.


Science China-physics Mechanics & Astronomy | 2016

Large unsaturated positive and negative magnetoresistance in Weyl semimetal TaP

Jianhua Du; Hangdong Wang; Qin Chen; Qianhui Mao; Rajwali Khan; Binjie Xu; Yuxing Zhou; Yannan Zhang; Jinhu Yang; Bin Chen; Chunmu Feng; Minghu Fang

After successfully growing single-crystal TaP, we measured its longitudinal resistivity (ρxx) and Hall resistivity (ρyx) at magnetic fields up to 9 T in the temperature range of 2-300 K. At 8 T, the magnetoresistance (MR) reached 3.28 × 105% at 2 K, 176% at 300 K. Neither value appeared saturated. We confirmed that TaP is a hole-electron compensated semimetal with a low carrier concentration and high hole mobility of μh=3.71 × 105 cm2/V s, and found that a magnetic-field-induced metal-insulator transition occurs at room temperature. Remarkably, because a magnetic field (H) was applied in parallel to the electric field (E), a negative MR due to a chiral anomaly was observed and reached -3000% at 9 T without any sign of saturation, either, which is in contrast to other Weyl semimetals (WSMs). The analysis of the Shubnikov-de Haas (SdH) oscillations superimposed on the MR revealed that a nontrivial Berry’s phase with a strong offset of 0.3958, which is the characteristic feature of charge carriers enclosing a Weyl node. These results indicate that TaP is a promising candidate not only for revealing fundamental physics of the WSM state but also for some novel applications.

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Bin Chen

Hangzhou Normal University

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Jinhu Yang

Hangzhou Normal University

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