Author Affiliations
Abstract
1 School of Physics, Henan Normal University, Xinxiang 453007, China
2 MOE Key Laboratory of Weak-Light Nonlinear Photonics, TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China
3 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
4 Institute of Physics, Henan Academy of Sciences, Zhengzhou 450046, China
5 e-mail: phyzhxd@gmail.com
6 e-mail: tanya@nankai.edu.cn
7 e-mail: zl-zhu@htu.edu.cn
Higher-order exceptional points (EPs), which appear as multifold degeneracies in the spectra of non-Hermitian systems, are garnering extensive attention in various multidisciplinary fields. However, constructing higher-order EPs still remains a challenge due to the strict requirement of the system symmetries. Here we demonstrate that higher-order EPs can be judiciously fabricated in parity–time ()-symmetric staggered rhombic lattices by introducing not only on-site gain/loss but also non-Hermitian couplings. Zero-energy flatbands persist and symmetry-protected third-order EPs (EP3s) arise in these systems owing to the non-Hermitian chiral/sublattice symmetry, but distinct phase transitions and propagation dynamics occur. Specifically, the EP3 arises at the Brillouin zone (BZ) boundary in the presence of on-site gain/loss. The single-site excitations display an exponential power increase in the -broken phase. Meanwhile, a nearly flatband sustains when a small lattice perturbation is applied. For the lattices with non-Hermitian couplings, however, the EP3 appears at the BZ center. Quite remarkably, our analysis unveils a dynamical delocalization-localization transition for the excitation of the dispersive bands and a quartic power increase beyond the EP3. Our scheme provides a new platform toward the investigation of the higher-order EPs and can be further extended to the study of topological phase transitions or nonlinear processes associated with higher-order EPs.
Photonics Research
2023, 11(2): 225
Author Affiliations
Abstract
1 College of Physics &
2 Electronic Engineering, Xinyang Normal University, Xinyang 464000
Considering the changes of the geometric shielding effect in a molecule as the incident electron energy varing, an empirical fraction, which is dependent on the incident electron energy, is presented. Using this empirical fraction, the total cross sections (TCSs) for electrons scattering from complex polyatomic molecules C2F4 and SO2 are calculated over a wide energy range from 30 to 5000 eV together with the additivity rule model at Hartree-Fock level. In the TCS calculations, the atoms are presented by the spherical complex optical potential, which is composed of static, exchange, polarization and absorption contributions. The quantitative TCSs above 100 eV are in good agreement with those obtained by experiments and other theories. It is proved that the empirical fraction, which exhibits the TCS contributions of shielded atoms in a molecule at different energies, is reasonable.
020.2070 Effects of collisions 020.0020 Atomic and molecular physics Chinese Optics Letters
2006, 4(4): 04192
Author Affiliations
Abstract
1 College of Physics and Electronic Engineering, Xinyang Normal University, Xinyang 464000
2 College of Physics and Information Engineering, Henan Normal University, Xinxiang 453007
3 Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065
The total (elastic plus inelastic) cross sections for positron scattering from N2 and CO2 over the incident energy range from 30 to 3000eV are calculated using the additivity rule model at Hartree-Fock level. A complex optical model potential modified by incorporating the concept of bonded atom, which takes into account the overlapping effect of electron clouds between two atoms in a molecule, is employed to calculate the total cross section of positron-molecule scattering. The calculated total cross sections are in good agreement with those reported by experiments and other theories over a wide energy range.
020.2070 effects of collisions 020.0020 atomic and molecular physics Chinese Optics Letters
2006, 4(3): 03125
Author Affiliations
Abstract
1 College of Physics & Electronic Engineering, Xinyang Normal University, Xinyang 464000
2 College of Physics & Information Engineering, Henan Normal University, Xinyang 453007
3 Institute of Atomic and Morlecular Physics, Sichuan University, Chengdu 610065
The accurate dissociation energy and equilibrium geometry of the b3Π state of 7LiH molecule is calculated using a symmetry-adapted-cluster configuration-interaction method in full active space. And the calculated results are 0.2580 eV and 0.1958 nm for the dissociation energy and equilibrium geometry, respectively. The whole potential energy curve for the b3Π state is also calculated over the internuclear separation range from about 0.10 to 0.54 nm. The results are fitted by the Murrell-Sorbie function. It is found that the Murrell-Sorbie function form, which is mainly used to fit the ground-state potential energy function, is well suitable for the excited triplet b3Π state. The vertical excitation energy from the ground state to the b3Π state is calculated to be 4.233 eV. Based on the analytic potential energy function, the harmonic frequency of 610.88 cm^(-1) about this state is firstly estimated. Compared with other theoretical results, this work is the most complete effort to deal with the analytic potential energy function and the harmonic frequency of this state.
020.2070 effects of collisions 020.7010 trapping Chinese Optics Letters
2005, 3(12): 12683
Author Affiliations
Abstract
1 College of Physics and Electronic Engineering, Xinyang Normal University, Xinyang 464000
2 Department of Physics, Henan Normal University, Xinxiang 453007
Total cross sections (TCSs) of electrons scattering from triatomic molecules over the energy range from 30 to 5000 eV are investigated employing a new semi-empirical formula. The TCSs of electrons scattering from triatomic molecules SO2, NO2, and CO2 are calculated. The quantitative TCSs are in good agreement with those obtained by experiments. It is shown that the results derived from the semi-empirical formula are much closer to the measurements than other calculations.
020.2070 effects of collisions 020.0020 atomic and molecular physics Chinese Optics Letters
2005, 3(8): 08438
Author Affiliations
Abstract
1 Department of Physics &
2 Electronic Engineering, Xinyang Teachers' College, Xinyang 464000
3 Department of Physics, Henan Normal University, Xinxiang 453007
A complex optical model potential correlated by the concept of bonded atoms, which considers the overlapping effect of electron clouds between two atoms in a molecule, is firstly employed to calculate the absolute differential cross sections, the integrated and momentum transfer cross sections for electrons scattered by O2 at intermediate and high energies by using additivity rule model at Hartree-Fock level. In the study, the complex optical model potential is composed of static, exchange, correlation polarization plus absorption contributions. The quantitative absolute differential cross sections, the integrated and momentum transfer cross sections are obtained. Compared with available experimental data, this approach presents good results. It is shown that the additivity rule model together with the complex optical model potential correlated by the concept of bonded atoms is completely suitable for the calculations of the absolute differential cross sections, the integrated and momentum transfer cross sections.
020.2070 effects of collisions 020.0020 atomic and molecular physics Chinese Optics Letters
2005, 3(1): 0101
Author Affiliations
Abstract
1 Department of Physics, Henan Normal University, Xinxiang 453002
2 Department of Foundation, The First Aeronautical College of Air Force, Xinyang 464000
A model complex optical potential rewritten by the conception of bonded atom, which considers the overlapping effect of electron cloud, is employed to calculate the total (elastic + inelastic) cross sections with simple molecules (N_(2), O_(2), NO_(2), NO, N_(2)O) consisting of N & O atoms over an incident energy range of 100 - 1600 eV by the use of additivity rule at Roothaan-Hartree-Fock level. In the study, the complex optical potential composed of static, exchange, correlation polarization plus absorption contributions firstly uses bonded-atom conception. The qualitative results are compared with experimental data and other calculations wherever available and good agreement is obtained. The total cross sections of electronmolecule scattering above 100 eV can be successfully calculated.
020.2070 effects of collisions 020.0020 atomic and molecular physics Chinese Optics Letters
2003, 1(11): 11624
