School of Physics and Optoelectronics, Xiangtan University, Xiangtan, Hunan 411105, China.
Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore.
Nat Commun. 2017 Jun 5;8:15641. doi: 10.1038/ncomms15641.
Carbon, the basic building block of our universe, enjoys a vast number of allotropic structures. Owing to its bonding characteristic, most carbon allotropes possess the motif of hexagonal rings. Here, with first-principles calculations, we discover a new metastable three-dimensional carbon allotrope entirely composed of pentagon rings. The unique structure of this Pentagon Carbon leads to extraordinary electronic properties, making it a cornucopia of emergent topological fermions. Under lattice strain, Pentagon Carbon exhibits topological phase transitions, generating a series of novel quasiparticles, from isospin-1 triplet fermions to triply degenerate fermions and further to Hopf-link Weyl-loop fermions. Its Landau level spectrum also exhibits distinct features, including a huge number of almost degenerate chiral Landau bands, implying pronounced magneto-transport signals. Our work not only discovers a remarkable carbon allotrope with highly rare structural motifs, it also reveals a fascinating hierarchical particle genesis with novel topological fermions beyond the Dirac and Weyl paradigm.
碳是宇宙的基本组成部分，拥有多种同素异形体。由于其成键特性，大多数碳同素异形体都具有六边形环的特征。在这里，我们通过第一性原理计算发现了一种全新的、亚稳的三维碳同素异形体，它完全由五边形环组成。这种五角形碳的独特结构带来了非凡的电子性质，使其成为新兴拓扑费米子的宝库。在晶格应变下，五角形碳会发生拓扑相变，产生一系列新的准粒子，从同位旋三重态费米子到三重简并费米子，再到 Hopf 链接 Weyl 环费米子。它的朗道能级谱也具有独特的特征，包括大量几乎简并的手性朗道能带，这意味着存在显著的磁输运信号。我们的工作不仅发现了一种具有罕见结构特征的优异碳同素异形体，还揭示了一种引人入胜的层次化粒子生成过程，其中包含了超越狄拉克和外尔范式的新型拓扑费米子。
