Dirac-cone-like electronic states on nematic antiferromagnetic FeSe and FeTe.

We investigate the Dirac-cone-like (DCL) topological electronic properties of nematic-like antiferromagnetic (AFM) states of monolayer FeSe and FeTe designed artificially through first-principles calculations and Wannier-function-based tight-binding (WFTB) method. Our calculations reveal most of them have a pair of DCL bands on the Γ-Xline in the Brillouin zone (BZ) near the Fermi level and open a gap of about 20 meV in the absence and presence of spin-orbit coupling (SOC), respectively, similar to the lowest-energy pair-checkerboard AFM FeSe. We further confirm that they are weak topological insulators based on nonzeroZ2and fragile surface states, which are calculated by the WFTB method. For FeSe and FeTe in pair-checkerboard AFM states, we find that the in-plane compression strain in a certain range can give rise to another pair of DCL bands located on the Γ-X' line in the BZ. In addition, the magnetic moments, energies, and Fe-Se/Te distances for various nematic-like AFM configurations are presented. These calculations the combining effect of magnetism and topology in a single material and the understanding of the superconducting phenomena in iron-based FeSe and FeTe.

Magnetic field effect on topological properties of Dirac semimetals PdTe2/PtTe2/PtSe2.

We investigated magnetic field effect on the topological properties of transition metal dichalcogenide Dirac semimetals (DSMs) PdTe2/PtTe2/PtSe2based on Wannier-function-based tight-binding (WFTB) model obtained from first-principles calculations. The DSMs PdTe2/PtTe2/PtSe2undergo a transition from DSMs into Weyl semimetals with four pairs of Weyl points (WPs) in the entire Brillouin zone by splitting Dirac points under external magnetic fieldB. The positions and energies of WPs vary linearly with the strength of theBfield under thec-axis magnetic fieldB. Under thea- andb-axisBfield, however, the positions of magnetic-field-inducing WPs deviate slightly from thecaxis, and theirkzcoordinates and energies change in a parabolic-like curve with the increasingBfield. However, the system opens an axial gap on theA-Γ axis, and the gap changes with the direction of theBfield when the out ofc-axisBfield is applied. When we further apply the magnetic field in theac,bc, andabplanes, the results are more diverse compared to the axial magnetic field. Under theacandbcplaneBfield, thekzand energies of WPs within angleθ= [0°, 90°] andθ= [90°, 180°] are mirror symmetrically distributed. The distribution of WPs shows broken rotational symmetry under theabplaneBfield due to the difference of non-diagonal part of Hamiltonian. Our theoretical findings can provide a useful guideline for the applications of DSM materials under external magnetic field in the future topological electronic devices.