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Effective Hamiltonian of Topological Nodal Line Semimetal in Single-Component Molecular Conductor [Pd(dddt) <sub/>2</sub> ] from First-Principles
摘要： Using ?rst-principles density-functional theory calculations, we obtain the non-coplanar nodal loop for a single-component molecular conductor [Pd(dddt)2] consisting of HOMO and LUMO with di?erent parity. Focusing on two typical Dirac points, we present a model of an e?ective 2 × 2 matrix Hamiltonian in terms of two kinds of velocities associated with the nodal line. The base of the model is taken as HOMO and LUMO on each Dirac point, where two band energies degenerate and the o? diagonal matrix element vanishes. The present model, which reasonably describes the Dirac cone in accordance with the ?rst-principles calculation, provides a new method of analyzing electronic states of a topological nodal line semimetal.
关键词： topological nodal line semimetal,effective Hamiltonian,Dirac cone,single-component molecular conductor,first-principles calculations
更新于2025-09-23 15:21:21
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Experimental Realization of Two-Dimensional Buckled Lieb lattice
摘要： Two-dimensional (2D) materials with a Lieb lattice host exotic electronic band structures. Such a system does not exist in nature, and it is also difficult to obtain in the laboratory due to its structural instability. Here, we experimentally realized a 2D system composed of a tin overlayer on an aluminum substrate by molecular beam epitaxy. The specific arrangement of Sn atoms on the Al(100) surface, which benefits from favorable interface interactions, forms a stabilized buckled Lieb lattice. Theoretical calculations indicate a partially broken nodal line loop and a topologically nontrivial insulating state with a spin-orbital coupling effect in the band structure of this Lieb lattice. The electronic structure of this system is experimentally characterized by angle-resolved photoemission spectroscopy, in which the hybridized states between topmost Al atoms and Sn atoms are revealed. Our work provides an appealing method for constructing 2D quantum materials based on the Lieb lattice.
关键词： Lieb lattice,nodal line,geometry,topological insulating state,spin-orbital coupling,2D materials
更新于2025-09-23 15:19:57
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Optical signatures of Dirac nodal lines in NbAs <sub/>2</sub>
摘要： Using polarized optical and magneto-optical spectroscopy, we have demonstrated universal aspects of electrodynamics associated with Dirac nodal lines that are found in several classes of unconventional intermetallic compounds. We investigated anisotropic electrodynamics of NbAs2 where the spin-orbit coupling (SOC) triggers energy gaps along the nodal lines. These gaps manifest as sharp steps in the optical conductivity spectra σ1(ω). This behavior is followed by the linear power-law scaling of σ1(ω) at higher frequencies, consistent with our theoretical analysis for dispersive Dirac nodal lines. Magneto-optics data affirm the dominant role of nodal lines in the electrodynamics of NbAs2.
关键词： Dirac fermions,nodal-line semimetal,optical conductivity,magneto-optics
更新于2025-09-09 09:28:46