Li Xinru, Dai Ying, Ma Yandong, Huang Baibiao
School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, People's Republic of China.
Phys Chem Chem Phys. 2014 Jul 14;16(26):13383-9. doi: 10.1039/c4cp01512f.
p-Electron-based monolayer materials have dominated the research of Dirac fermions since the first exfoliation of graphene. In the present work, the electronic and magnetic properties of d-electron-based Dirac systems are studied by combining first-principles with mean field theory and Monte Carlo approaches. From first-principles calculations, we demonstrate that transition-metal (TM) monolayers (TM = Ti, Zr, Hf, V, Nb, or Ta), d-electron-based materials, could also hold Dirac cones and not only p-electron-based materials as known before. This may shed light on the breakthrough of new nanomaterials with d-type Dirac points. Moreover, the carrier mobility near the Dirac points of these materials can be tuned regularly by isotropic strains from -5% to 5%, without breaking the Dirac cones. However, the Dirac points would disappear under anisotropic strains, indicating that a rigorous honeycomb lattice may be the main precondition for Dirac points in TM-monolayers. Furthermore, some TM-monolayers (TM = Ti, Zr, or Hf) exhibit ferromagnetic couplings simultaneously. In addition, by mean field theory and Monte Carlo methods, it is found that Curie temperatures of TM-monolayers can be higher than 580 K even to 1180 K. Our findings significantly expand the Dirac systems.
自石墨烯首次被剥离以来，基于p电子的单层材料主导了狄拉克费米子的研究。在本工作中，通过将第一性原理与平均场理论和蒙特卡罗方法相结合，研究了基于d电子的狄拉克体系的电子和磁性特性。从第一性原理计算中，我们证明了过渡金属（TM）单层（TM = Ti、Zr、Hf、V、Nb或Ta），即基于d电子的材料，也可以拥有狄拉克锥，而不仅仅是如之前所知的基于p电子的材料。这可能为具有d型狄拉克点的新型纳米材料的突破提供线索。此外，这些材料狄拉克点附近的载流子迁移率可以通过-5%至5%的各向同性应变进行有规律的调节，而不会破坏狄拉克锥。然而，在各向异性应变下狄拉克点会消失，这表明严格的蜂窝晶格可能是TM单层中存在狄拉克点的主要前提条件。此外，一些TM单层（TM = Ti、Zr或Hf）同时表现出铁磁耦合。另外，通过平均场理论和蒙特卡罗方法发现，TM单层的居里温度可以高于580 K，甚至达到1180 K。我们这一发现显著扩展了狄拉克体系。
