arXiv subjects

H. P. Wang

Publications and source records attributed to H. P. Wang.

13 recordsLinked to original sources

arXiv2025

SIP-IFVM: Efficient time-accurate magnetohydrodynamic model of the corona and coronal mass ejections

In this paper, we present an efficient and time-accurate three-dimensional (3D) single-fluid MHD solar coronal model and employ it to simulate CME evolution and propagation. Based on a quasi-steady-state implicit MHD coronal model, we developed an efficient time-accurate coronal model that can be used to speed up the CME simulation by selecting a large time-step size. We have called it the Solar Interplanetary Phenomena-Implicit Finite Volume Method (SIP-IFVM) coronal model. A pseudo-time marching method was implemented to improve temporal accuracy. A regularised Biot-Savart Laws (RBSL) flux rope, whose axis can be designed into an arbitrary shape, was inserted into the background corona to trigger the CME event. We performed a CME simulation on the background corona of Carrington rotation (CR) 2219 and evaluated the impact of time-step sizes on simulation results. Our study demonstrates that this model is able to simulate the CME evolution and propagation process from the solar surface to $20\; R_s$ in less than 0.5 hours (192 CPU cores, $\sim$ 1 M cells). Compared to the explicit counterpart, this implicit coronal model is not only faster, but it also has improved numerical stability. We also conducted an ad hoc simulation with initial magnetic fields artificially increased. It shows that this model can effectively deal with time-dependent low-$β$ problems ($β<10^{-4}$). Additionally, an Orszag-Tang MHD vortex flow simulation demonstrates that the pseudo-time-marching method used in this coronal model can simulate small-scale unsteady-state flows. The simulation results show that this MHD coronal model is very efficient and numerically stable. It is a promising approach to simulating time-varying events in the solar corona with low plasma $β$ in a timely and accurate manner.

astro-ph.SR↗

arXiv2022

Track-based alignment for the BESIII CGEM detector in the cosmic-ray test

The Beijing Electron Spectrometer III (BESIII) is a multipurpose detector operating on the Beijing Electron Positron Collider II (BEPCII). After more than ten year's operation, the efficiency of the inner layers of the Main Drift Chamber (MDC) decreased significantly. To solve this issue, the BESIII collaboration is planning to replace the inner part of the MDC with three layers of Cylindrical triple Gas Electron Multipliers (CGEM). The transverse plane spatial resolution of CGEM is required to be 120 $μ$m or better. To meet this goal, a careful calibration of the detector is necessary to fully exploit the potential of the CGEM detector. In all the calibrations, the detector alignment plays an important role to improve the detector precision. The track-based alignment for the CGEM detector with the Millepede algorithm is implemented to reduce the uncertainties of the hit position measurement. Using the cosmic-ray data taken in 2020 with the two layers setup, the displacement and rotation of the outer layer with respect to the inner layer is determined by a simultaneous fit applied to more than 160000 tracks. A good alignment precision has been achieved that guarantees the design request could be satisfied in the future. A further alignment is going to be performed using the combined information of tracks from cosmic-ray and collisions after the CGEM is installed into the BESIII detector.

hep-ex↗

arXiv2017

Single crystal growth and physical property characterizations of mixed valent compound YbFe$_2$Al$_{10}$

We report single crystal growth and physical properties characterization of YbFe$_2$Al$_{10}$ compounds. The measurements of resistivity, magnetic susceptibility, and specific heat show different behaviors from previous studies on polycrystal samples. A mixed valent characteristic with moderate mass enhancement is indicated. In particular, the optical spectroscopy measurement reveals formation of multiple hybridization energy gaps which become progressively pronounced at low temperature. The multiple hybridization energy gaps are likely caused by the hybridizations between the flat band from Yb 4$f$ electrons and different bands of conduction electrons.

cond-mat.str-el↗

arXiv2017

Prediction of High Temperature Quantum Anomalous Hall Effect in Two Dimensional Transition-Metal Oxides

Quantum anomalous Hall (QAH) insulator is a topological phase which exhibits chiral edge states in the absence of magnetic field. The celebrated Haldane model is the first example of QAH effect, but difficult to realize. Here, we predict the two-dimensional single-atomic-layer V2O3 with a honeycomb-Kagome structure is a QAH insulator with a large band gap (large than 0.1 eV) and a high ferromagnetic Curie temperature (about 900 K). Combining the first-principle calculations with the effective Hamiltonian analysis, we find that the spin-majority dxy and dyz orbitals of V atoms on the honeycomb lattice form a massless Dirac cone near the Fermi level which becomes massive when the on-site spin-orbit coupling is included. Interestingly, we find that the large band gap is caused by a cooperative effect of electron correlation and spin-orbit coupling. Both first-principle calculations and the effective Hamiltonian analysis confirm that 2D V2O3 has a non-zero Chern number (i.e., one). Our work paves a new direction towards realizing the QAH effect at room temperature.

cond-mat.mtrl-sci↗

arXiv2017

Optical spectroscopy study of charge density wave order in Sr$_{3}$Rh$_{4}$Sn$_{13}$ and (Sr$_{0.5}$Ca$_{0.5}$)$_{3}$Rh$_{4}$Sn$_{13}$

We perform optical spectroscopy measurement across the charge density wave (CDW) phase transitions on single-crystal samples of Sr$_{3}$Rh$_{4}$Sn$_{13}$ and (Sr$_{0.5}$Ca$_{0.5}$)$_{3}$Rh$_{4}$Sn$_{13}$. Formation of CDW energy gap was clearly observed for both single-crystal samples when they undergo the phase transitions. The existence of a Drude component in $σ_1(ω)$ below \TCDW indicates that the Fermi surface is only partially gapped in the CDW state. The obtained value of 2$Δ$/K$_{B}$T$_{CDW}$ is roughly 13 for both Sr$_{3}$Rh$_{4}$Sn$_{13}$ and (Sr$_{0.5}$Ca$_{0.5}$)$_{3}$Rh$_{4}$Sn$_{13}$ compounds. The value is considerably larger than the mean-field value based on the weak-coupling BCS theory. The observed spectral feature in (Sr$_{x}$Ca$_{1-x}$)$_{3}$Rh$_{4}$Sn$_{13}$ resembles those seen in many other CDW systems.

cond-mat.supr-con↗

arXiv2016

Anisotropic transport and optical spectroscopy study on antiferromagentic triangular lattice EuCd_2As_2: an interplay between magnetism and charge transport properties

We present anisotropic transport and optical spectroscopy studies on EuCd_2As_2. The measurements reveal that EuCd_2As_2 is a low carrier density semimetal with moderate anisotropic resistivity ratio. The charge carriers experience very strong scattering from Eu magnetic moments, resulting in a Kondo-like increase of resistivity at low temperature. Below the antiferromagnetic transition temperature at $T_N$= 9.5 K, the resistivity drops sharply due to the reduced scattering from the ordered Eu moments. Nevertheless, the anisotropic ratio of $ρ_c/ρ_{ab}$ keeps increasing, suggesting that the antiferromagnetic coupling is along the c-axis. The optical spectroscopy measurement further reveals, besides an overdamped reflectance plasma edge at low energy, a strong coupling between phonon and electronic continuum. Our study suggests that EuCd_2As_2 is a promising candidate displaying intriguing interplay among charge, magnetism and the underlying crystal lattice.

cond-mat.str-el↗

arXiv2015

Optical properties of TlNi2Se2: Observation of pseudogap formation

The quasi-two-dimensional nickel chalcogenides $TlNi_2Se_2$ is a newly discovered superconductor. We have performed optical spectroscopy study on $TlNi_2Se_2$ single crystals over a broad frequency range at various temperatures. The overall optical reflectance spectra are similar to those observed in its isostructure $BaNi_2As_2$. Both the suppression in $R(ω)$ and the peaklike feature in $σ_1(ω)$ suggest the progressive formation of a pseudogap feature in the midinfrared range with decreasing temperatures, which might be originated from the dynamic local fluctuation of charge-density-wave (CDW) instability. We propose that the CDW instability in $TlNi_2Se_2$ is driven by the saddle points mechanism, due to the existence of van Hove singularity very close to the Fermi energy.

cond-mat.supr-con↗

arXiv2014

Coexistence of superconductivity and density wave in $\mathrm{Ba_2Ti_2Fe_2As_4O}$: an optical spectroscopy study

We performed an optical spectroscopy measurement on single crystals of $\mathrm{Ba_2Ti_2Fe_2As_4O}$, which is a newly discovered superconductor showing a coexistence of superconductivity and density wave order. The study reveals a spectral change related to the formation density wave energy gap below $T_{DW}\approx$125 K, leading to the removal of about half of the multiple Fermi surface sheets. The ratio of 2$Δ_{DW}$/$k_B T_{DW}\approx$ 11.9 is considerably larger than the mean-field value based on the weak-coupling BCS theory. At the lowest temperature in the superconducting state, we observed opening of superconducting energy gaps $Δ_1(0) =3.4$ meV and $Δ_2(0)=7.9$ meV. The properties of superconducting state in $\mathrm{Ba_2Ti_2Fe_2As_4O}$ are similar to that in $\mathrm{BaFe_{1.85}Co_{0.15}As_2}$.

cond-mat.supr-con↗

arXiv2014

Optical spectroscopy study of the collapsed tetragonal phase of CaFe$_2$(As$_{0.935}$P$_{0.065}$)$_2$ single crystals

We present an optical spectroscopy study on P-doped CaFe$_2$As$_2$ which experiences a structural phase transition from tetragonal to collapsed tetragonal (cT) phase near 75 K. The measurement reveals a sudden reduction of low frequency spectral weight and emergence of a new feature near 3200 \cm (0.4 eV) in optical conductivity across the transition, indicating an abrupt reconstruction of band structure. The appearance of new feature is related to the interband transition arising from the sinking of hole bands near $Γ$ point below Fermi level in the cT phase, as expected from the density function theory calculations in combination with the dynamical mean field theory. However, the reduction of Drude spectral weight is at variance with those calculations. The measurement also indicates an absence of the abnormal spectral weight transfer at high energy (near 0.5-0.7 eV) in the cT phase, suggesting a suppression of electron correlation effect.

cond-mat.supr-con↗

arXiv2014

Optical spectroscopy study of Nd(O,F)BiS2 single crystals

We present an optical spectroscopy study on F-substituted NdOBiS$_2$ superconducting single crystals grown using KCl/LiCl flux method. The measurement reveals a simple metallic response with a relatively low screened plasma edge near 5000 \cm. The plasma frequency is estimated to be 2.1 eV, which is much smaller than the value expected from the first-principles calculations for an electron doping level of x=0.5, but very close to the value based on a doping level of 7$\%$ of itinerant electrons per Bi site as determined by ARPES experiment. The energy scales of the interband transitions are also well reproduced by the first-principles calculations. The results suggest an absence of correlation effect in the compound, which essentially rules out the exotic pairing mechanism for superconductivity or scenario based on the strong electronic correlation effect. The study also reveals that the system is far from a CDW instability as being widely discussed for a doping level of x=0.5.

cond-mat.supr-con↗

arXiv2014

Revealing multiple density wave orders in non-superconducting titanium oxypnictide Na$_2$Ti$_2$As$_2$O

We report an optical spectroscopy study on the single crystal of Na$_2$Ti$_2$As$_2$O, a sister compound of superconductor BaTi$_2$Sb$_2$O. The study reveals unexpectedly two density wave phase transitions. The first transition at 320 K results in the formation of a large energy gap and removes most part of the Fermi surfaces. But the compound remains metallic with residual itinerant carriers. Below 42 K, another density wave phase transition with smaller energy gap scale occurs and drives the compound into semiconducting ground state. These experiments thus enable us to shed light on the complex electronic structure in the titanium oxypnictides.

cond-mat.str-el↗

arXiv2013

Formation of the density wave energy gap in Na$_2$Ti$_2$Sb$_2$O: an optical spectroscopy study

We performed optical spectroscopy measurement on single crystals of Na$_2$Ti$_2$Sb$_2$O, which is the parent compound for the newly discovered Ti-based superconductors. The study reveals significant spectral change across the phase transition at 114 K and formation of a density-wave type energy gap. The opening of the gap removes most part of the free carrier spectral weight and causes a dramatic reduction of the carrier scattering rate. The ratio of 2$Δ/k_BT_s\approx$14 is considerably larger than the mean-field value based on the weak-coupling BCS theory. The study also reveals a weak correlation effect in the titanium oxypnictides.

cond-mat.supr-con↗

arXiv2012

Single crystal growth and optical conductivity of SrPt$_2$As$_2$ superconductors

SrPt$_2$As$_2$ single crystals with CaBe$_2$Ge$_2$-type structure were synthesized by self-melting technique. X-ray diffraction, transmission electron microscopy, electrical resistivity, specific heat and optical spectroscopy measurements were conducted to elucidate the properties of SrPt$_2$As$_2$. SrPt$_2$As$_2$ single crystals exhibit a superconducting transition at 5.2K, experiencing a structural phase transition well above room temperature (about 455K). The superconducting and structural phase transition temperatures are both reduced by 6% Iridium doping. Both pure SrPt$_2$As$_2$ and the doped single crystals are revealed to be highly metallic with rather high plasma frequencies. In particular, the optical spectroscopy measurement revealed two gap-like suppression features. We elaborated that the one at higher energy scale could be ascribed to the correlation effect, while the other one at lower energy scale is related to the structural phase transition, leading to the removal of a small portion of the Fermi surfaces.

cond-mat.supr-con↗