Zhu Pangdong, Bu Kun, Wang Ruzhi, Wang Changhao
Key Laboratory of Advanced Functional Materials of Education Ministry of China, Institute of Advanced Energy Materials and Devices, College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China.
School of Physics and Optoelectronic Engineering, Shandong University of Technology, Zibo 255000, China.
Phys Chem Chem Phys. 2024 Sep 18;26(36):23600-23608. doi: 10.1039/d4cp02362e.
Topological semimetals have garnered significant interest due to their intrinsic topological physics and potential applications in devices. A crucial feature shared by all topological materials is the bulk-boundary correspondence, indicating the presence of unique topologically protected conducting states at the edges when non-trivial band topology exists in the bulk. Previous studies on surface states of topological materials predominantly focused on pristine surfaces, leaving the exploration of surface states in topological semimetals with adsorbates relatively uncharted. This work, based on calculations, examines variations in the topological surface states of MgB, a well-known conventional superconductor and topological nodal line semimetal. We employ a thick slab model with Mg/B atoms as surface terminations to simulate its topological surface states. Subsequently, we investigate the adsorption of hydrogen (H), hydroxide (OH), and water (HO) on the surface slabs to observe changes in the surface states. The pristine slab model gives the drumhead-like surface states inside the surface projected nodal lines, while the topological surface states change differently after adsorbing H, OH, and HO, which can be understood systematically by combining the surface adsorption Gibbs free energy Δ, surface terminations, and surface charge density distributions. Especially, our findings suggest that the Bader charge transfer value of surface atoms providing topological states is a key indicator for evaluating the variation in topological surface states after adsorption. This study provides a systematic understanding of the topological surface states of MgB with different adsorbates, paving the way for future theoretical and experimental investigations in related fields and shedding light on the potential device applications of topological materials.
拓扑半金属因其内在的拓扑物理性质和在器件中的潜在应用而备受关注。所有拓扑材料共有的一个关键特征是体-边界对应，这表明当体中存在非平凡能带拓扑时，边缘处会存在独特的拓扑保护导电态。先前对拓扑材料表面态的研究主要集中在原始表面，而对吸附有吸附质的拓扑半金属表面态的探索相对较少。这项工作基于计算，研究了著名的传统超导体和拓扑节线半金属MgB₂的拓扑表面态的变化。我们采用以Mg/B原子作为表面终端的厚平板模型来模拟其拓扑表面态。随后，我们研究了氢（H）、氢氧根（OH）和水（H₂O）在表面平板上的吸附情况，以观察表面态的变化。原始平板模型在表面投影节线内部给出了鼓面状的表面态，而吸附H、OH和H₂O后拓扑表面态的变化不同，这可以通过结合表面吸附吉布斯自由能Δ、表面终端和表面电荷密度分布来系统地理解。特别是，我们的研究结果表明，提供拓扑态的表面原子的巴德电荷转移值是评估吸附后拓扑表面态变化的关键指标。这项研究为理解具有不同吸附质的MgB₂的拓扑表面态提供了系统的认识，为未来相关领域的理论和实验研究铺平了道路，并为拓扑材料的潜在器件应用提供了启示。
