Publications by authors named "Jianqun Yang"

11 Publications

  • Page 1 of 1

Quantum Monte Carlo study of the Hubbard model with next-nearest-neighbor hopping t': pairing and magnetism.

J Phys Condens Matter 2021 Mar;33(11):115601

School of Physics, Harbin Institute of Technology, Harbin, 150001, People's Republic of China.

Using the finite-temperature determinant quantum Monte Carlo (DQMC) algorithm, we study the pairing symmetries of the Hubbard Hamiltonian with next-nearest-neighbor (NNN) hopping t' on square lattices. By varying the value of t', we find that the d-wave pairing is suppressed by the onset of t', while the p + ip-wave pairing tends to emerge for low electron density and t' around -0.7. Together with the calculation of the anti-ferromagnetic and ferromagnetic spin correlation function, we explore the relationship between anti-ferromagnetic order and the d-wave pairing symmetry, and the relationship between ferromagnetic order and the p + ip-wave pairing symmetry. Our results may be useful for the exploration of the mechanism of the electron pairing symmetries, and for the realization of the exotic p + ip-wave superconductivity.
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http://dx.doi.org/10.1088/1361-648X/abd33aDOI Listing
March 2021

Study on the Microstructure of Polyether Ether Ketone Films Irradiated with 170 keV Protons by Grazing Incidence Small Angle X-ray Scattering (GISAXS) Technology.

Polymers (Basel) 2020 Nov 17;12(11). Epub 2020 Nov 17.

School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China.

Polyether ether ketone (PEEK) films irradiated with 170 keV protons were calculated by the stopping and ranges of ions in matter (SRIM) software. The results showed that the damage caused by 170 keV protons was only several microns of the PEEK surface, and the ionization absorbed dose and displacement absorbed dose were calculated. The surface morphology and roughness of PEEK after proton irradiation were studied by atomic force microscope (AFM). GISAXS was used to analyze the surface structural information of the pristine and irradiated PEEK. The experimental results showed that near the surface of the pristine and irradiated PEEK exists a peak, and the peak gradually disappeared with the increasing of the angles of incidence and the peak changed after irradiation, which implies the 170 keV protons have an effect on PEEK structure. The influences of PEEK irradiated with protons on the melting temperature and crystallization temperature was investigated by differential scanning calorimetry (DSC). The DSC results showed that the crystallinity of the polymer after irradiation decreased. The structure and content of free radicals of pristine and irradiated PEEK were studied by Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). The stress and strain test results showed that the yield strength of the PEEK irradiated with 5 × 10 p/cm and 1 × 10 p/cm was higher than the pristine, but the elongation at break of the PEEK irradiated with 5 × 10 p/cm and 1 × 10 p/cm decreased obviously.
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http://dx.doi.org/10.3390/polym12112717DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7698423PMC
November 2020

PN/PAs-WSe van der Waals heterostructures for solar cell and photodetector.

Sci Rep 2020 Oct 14;10(1):17213. Epub 2020 Oct 14.

School of Physics, Harbin Institute of Technology, Harbin, 150001, China.

By first-principles calculations, we investigate the geometric stability, electronic and optical properties of the type-II PN-WSe and type-I PAs-WSe van der Waals heterostructures(vdWH). They are p-type semiconductors with indirect band gaps of 1.09 eV and 1.08 eV based on PBE functional respectively. By applying the external gate field, the PAs-WSe heterostructure would transform to the type-II band alignment from the type-I. With the increasing of magnitude of the electric field, two heterostructures turn into the n-type semiconductors and eventually into metal. Especially, PN/PAs-WSe vdWH are both high refractive index materials at low frequencies and show negative refractive index at high frequencies. Because of the steady absorption in ultraviolet region, the PAs-WSe heterostructure is a highly sensitive UV detector material with wide spectrum. The type-II PN-WSe heterostructure possesses giant and broadband absorption in the near-infrared and visible regions, and its solar power conversion efficiency of 13.8% is higher than the reported GaTe-InSe (9.1%), MoS/p-Si (5.23%) and organic solar cells (11.7%). It does project PN-WSe heterostructure a potential for application in excitons-based solar cells.
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http://dx.doi.org/10.1038/s41598-020-73152-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7560845PMC
October 2020

Modulation of the electronic band structure of silicene by polar two-dimensional substrates.

Phys Chem Chem Phys 2020 Sep;22(37):21412-21420

School of Physics, Harbin Institute of Technology, Harbin 150001, China.

Using the density functional theory (DFT) calculations, we find that  Janus group-III chalcogenide monolayers can serve as a suitable substrate for silicene, and the Dirac electron band properties of silicene are also fully preserved. The maximum opened band gap can reach 179 meV at the Dirac point due to the interaction of silicene and the polar two-dimensional (2D) substrate. In addition, the electronic band structure of the heterostructure can be modulated by applying an electric field where its predicted band gap increases or decreases according to the direction of the applied external electric field. Furthermore, an insight into the electron structures can be understood by analyzing the electron energy-loss (EEL) spectra. From these results, we also predict that heterostructures with polar 2D substrates have broad application prospects in multi-functional devices. Besides, Janus group-III chalcogenide monolayers can be used as good substrates for growing silicene and the modulation of the electronic structure can also be applied to nanodevices and optoelectronic devices.
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http://dx.doi.org/10.1039/d0cp03486jDOI Listing
September 2020

Enhanced Shift Currents in Monolayer 2D GeS and SnS by Strain-Induced Band Gap Engineering.

ACS Omega 2020 Jul 9;5(28):17207-17214. Epub 2020 Jul 9.

Chongqing Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Chongqing University, Huxi Campus, Chongqing 401331, China.

Group IV monochalcogenides exhibit spontaneous polarization and ferroelectricity, which are important in photovoltaic materials. Since strain engineering plays an important role in ferroelectricity, in the present work, the effect of equibiaxial strain on the band structure and shift currents in monolayer two-dimensional (2D) GeS and SnS has systematically been investigated using the first-principles calculations. The conduction bands of those materials are more responsive to strain than the valence bands. Increased equibiaxial compressive strain leads to a drastic reduction in the band gap and finally the occurrence of phase transition from semiconductor to metal at strains of -15 and -14% for GeS and SnS, respectively. On the other hand, tensile equibiaxial strain increases the band gap slightly. Similarly, increased equibiaxial compressive strain leads to a steady almost four times increase in the shift currents at a strain of -12% with direction change occurring at -8% strain. However, at phase transition from semiconductor to metal, the shift currents of the two materials completely vanish. Equibiaxial tensile strain also leads to increased shift currents. For SnS, shift currents do not change direction, just as the case of GeS at low strain; however, at a strain of +8% and beyond, direction reversal of shift currents beyond the band gap in GeS occur.
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http://dx.doi.org/10.1021/acsomega.0c01319DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7376894PMC
July 2020

Coherent Manipulation with Resonant Excitation and Single Emitter Creation of Nitrogen Vacancy Centers in 4H Silicon Carbide.

Nano Lett 2020 Aug 13;20(8):6142-6147. Epub 2020 Jul 13.

Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore.

Silicon carbide (SiC) has become a key player in the realization of scalable quantum technologies due to its ability to host optically addressable spin qubits and wafer-size samples. Here, we have demonstrated optically detected magnetic resonance (ODMR) with resonant excitation and clearly identified the ground state energy levels of the NV centers in 4H-SiC. Coherent manipulation of NV centers in SiC has been achieved with Rabi and Ramsey oscillations. Finally, we show the successful generation and characterization of single nitrogen vacancy (NV) center in SiC employing ion implantation. Our results highligh the key role of NV centers in SiC as a potential candidate for quantum information processing.
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http://dx.doi.org/10.1021/acs.nanolett.0c02342DOI Listing
August 2020

Low Dielectric Constant Polyimide Obtained by Four Kinds of Irradiation Sources.

Polymers (Basel) 2020 Apr 10;12(4). Epub 2020 Apr 10.

School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, China.

Irradiation is a good modification technique, which can be used to modify the electrical properties, mechanical properties, and thermal properties of polymer materials. The effects of irradiation on the electrical properties, mechanical properties, and structure of polyimide (PI) films were studied. PI films were irradiated by a 1 MeV electron, 3 MeV proton, 10 MeV proton, and 25 MeV carbon ion. Dielectric constant, dielectric loss, and resistance measurements were carried out to evaluate the changes in the electrical properties; moreover, the mechanical properties of the pristine and irradiated PI were analyzed by the tensile testing system. The irradiation induced chemical bonds and free radicals changes of the PI films were confirmed by the Fourier transform infrared (FTIR) spectra, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR). The dielectric constant of the PI films decreases with the increase of fluences by the four kinds of irradiation sources.
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http://dx.doi.org/10.3390/polym12040879DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7240422PMC
April 2020

Photosynthetic Characteristics and Uptake and Translocation of Nitrogen in Peanut in a Wheat-Peanut Rotation System Under Different Fertilizer Management Regimes.

Front Plant Sci 2019 7;10:86. Epub 2019 Feb 7.

State Key Laboratory of Crop Biology and College of Agronomy, Shandong Agricultural University, Tai'an, China.

Better management of N fertilizer is essential for improving crop productivity. Wheat ( L.)-peanut ( L.) relay intercropping rotation systems are a mainstay of the measures to improve the economic and food security situation in China. Therefore, a 2-year field study (2015-2017) was conducted to evaluate the effect of different N fertilizer management regimes on the photosynthetic characteristics and uptake and translocation of N in peanut in the wheat-peanut rotation system. We used common compound fertilizer (CCF) and controlled-release compound fertilizer (CRF) at the same N-PO-KO proportion (The contents of N, PO, and KO in the two kinds of fertilizer were 20, 15, and 10%, respectively.). The fertilizer was applied on the day before sowing, at the jointing stage or the flag leaf stage of winter wheat, and at the initial flowering stage of peanut in various proportions, with 0 kg N ha as the control. Results showed that split applications of N significantly increased leaf area index (LAI) and chlorophyll content and improved photosynthetic rate, thus increasing the pod yield of peanut. Topdressing N at the jointing stage (S1) or at the flag leaf stage of wheat (S2) and supplying part of the N at the initial flowering stage of peanut increased pod yield. Withholding N until the flag leaf stage (S2) did not negatively affect wheat grain yield; however, it increased N accumulation in each organ and N allocation proportions in the peanut pod, ultimately improving pod yield. With the same N-PO-KO proportion and equivalent amounts of nutrient, CRF can decreased malondialdehyde (MDA) and maintain a relatively high LAI and chlorophyll content at the late growth stage of peanut, prolong the functional period of peanut leaves and delay leaf senescence, resulting in an increase of pod yield over that with CCF. At S1, CRF resulted in a better pod yield than CCF by 9.4%, and at S2 it was 12.6% higher. In summary, applying N fertilizer in three splits and delaying the topdressing fertilization until the flag leaf stage of winter wheat increases total grain yields of wheat and peanut. This method could therefore be an appropriate N management strategy for wheat-peanut relay intercropping rotation systems in China.
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http://dx.doi.org/10.3389/fpls.2019.00086DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6374608PMC
February 2019

Ultra-fast annealing manipulated spinodal nano-decomposition in Mn-implanted Ge.

Nanotechnology 2019 Feb 30;30(5):054001. Epub 2018 Nov 30.

Harbin Institute of Technology, School of Materials Science and Engineering, 150001, Harbin, People's Republic of China. Laboratory for Space Environment and Physical Science, Research Center of Basic Space Science, Harbin Institute of Technology, 150001, Harbin, People's Republic of China. Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Bautzner Landstrasse 400, D-01328 Dresden, Germany.

In the present work, millisecond-range flash lamp annealing is used to recrystallize Mn-implanted Ge. Through systematic investigations of structural and magnetic properties, we find that the flash lamp annealing produces a phase mixture consisting of spinodally decomposed Mn-rich ferromagnetic clusters within a paramagnetic-like matrix with randomly distributed Mn atoms. Increasing the annealing energy density from 46, via 50, to 56 J cm causes the segregation of Mn atoms into clusters, as proven by transmission electron microscopy analysis and quantitatively confirmed by magnetization measurements. According to x-ray absorption spectroscopy, the dilute Mn ions within Ge are in d electronic configuration. This Mn-doped Ge shows paramagnetism, as evidenced by the unsaturated magnetic-field-dependent x-ray magnetic circular dichroism signal. Our study reveals how spinodal decomposition occurs and influences the formation of ferromagnetic Mn-rich Ge-Mn nanoclusters.
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http://dx.doi.org/10.1088/1361-6528/aaefb1DOI Listing
February 2019

Bright room temperature single photon source at telecom range in cubic silicon carbide.

Nat Commun 2018 10 5;9(1):4106. Epub 2018 Oct 5.

Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore.

Single-photon emitters (SPEs) play an important role in a number of quantum information tasks such as quantum key distributions. In these protocols, telecom wavelength photons are desired due to their low transmission loss in optical fibers. In this paper, we present a study of bright single-photon emitters in cubic silicon carbide (3C-SiC) emitting in the telecom range. We find that these emitters are photostable and bright at room temperature with a count rate of ~ MHz. Altogether with the fact that SiC is a growth and fabrication-friendly material, our result may be relevant for future applications in quantum communication technology.
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http://dx.doi.org/10.1038/s41467-018-06605-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6173757PMC
October 2018

Interaction between hydrogen and gallium vacancies in β-GaO.

Sci Rep 2018 Jul 4;8(1):10142. Epub 2018 Jul 4.

School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150001, China.

In this paper, the revised Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE06) is used to investigate the interaction between hydrogen with different concentrations and gallium vacancies in β-GaO. The hydrogen can compensate a gallium vacancy by forming hydrogen-vacancy complex. A gallium vacancy can bind up to four hydrogen atoms, and formation energies decrease as the number of hydrogen atoms increases. Hydrogen prefers to bind with three coordinated oxygen. The bonding energy and annealing temperatures of complexes containing more than two hydrogen atoms are computed, and show relatively high stability. In addition, vacancy concentrations increase with the increasing vapor pressures. This paper can effectively explain the hydrogen impact in β-GaO.
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http://dx.doi.org/10.1038/s41598-018-28461-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6031635PMC
July 2018
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