On October 7^th, Nature Materials published an article online, reporting the latest research findings of Prof. Xu Nan, a member of Institute for Advanced Study. The paper is entitled “Directional massless Dirac fermions in a layered van der Waals material with one-dimensional long-range order”.

Wuhan University is the first author affiliation. Yang Tianyu and Wan Qiang, the 2019 doctoral students in Institute for Advanced Study, and Yan Dayu, a doctoral student in Institute of Physics, Chinese Academy of Science are joint first authors. Xu Nan is the corresponding author. The research is funded by the National Key R&D Programme of China and the National Natural Science Foundation of China.

Since the successful exfoliation of graphene, layered van der Waals (vdW) materials have attracted researchers’ attention and become one of the central topics in condensed-matter physics and materials science. Due to the quantum size effect of electrons in the two-dimensional (2D) limit, vdW materials with nanosized thickness displaymany novel phenomena, including topological quantum state, 2D magnetic ordering, and unconventional superconductivity. Moreover, vdW materials can easily be processed into atomically thin layers, which can further be assembled into heterostructures with high designability and manipulability. The new properties hold great potential applications in the next generation of electronic devices at the nanoscale.

Using angle-resolved photoemission spectroscopy (ARPES), Xu Nan’s team observed that single crystalNbSi0.45Te2, a vdW material with layered structure, exhibits the electronic state of confinement under one-dimensional (1D) limits and discovered directional Dirac fermions quasi-particle with fourfold degeneracy. The mass of the quasi-particle is zero in particular directions, but is infinite in relevant vertical plane. Combiningscanning tunnelling microscopy and first-principles calculations, they elucidate that the directional Dirac fermions emerge from the stripe-like structure with 1D long-range order and are protected by non-symmorphic symmetry. Different from quasi-one-dimensional materials with three-dimensional (3D) long-range order, NbSi0.45Te2 only has 1D long-range translational symmetry, a new atomic arrangement of solid block, which distinguishes it from crystal, quasi-crystal and amorphous solid.

ARPES observed 1D massless Dirac fermions quasi-particle

The research reports 1D massless Dirac fermions quasi-particle with fourfold degeneracy for the first time and provides the design of van der Waals heterojunction with a new constituent NbSi0.45Te2 of 1D electronic states.Just as the editor of Nature Materials summarized, “The discovery of 1D Dirac energy band in layered van der Waals materials has extended the ‘arsenal’ of 2D materials.”

The work is supported by many research institutes. Shi Youguo, researcher in Institute of Physics, Chinese Academy of Science, provided high-quality single crystal NbSi0.45Te2. Prof. Jia Jinfeng, and Zheng Hao, researcher from Shanghai Jiao Tong University used scanning tunnelling microscopy to characterize sample stripe.Prof. Yu Rui from School of Physics and Technology, Wuhan University, and Prof. Shengyuan A. Yang and Doctor Si Li, from Singapore University of Technology and Design conducted first-principles calculations. Prof. Jin Hu, from University of Arkansas, America, and Prof. Zhiqiang Mao, from the Pennsylvania State University provided high-quality single crystal NbSi1/3Te2. ARPES experiment was accomplished in Dreamline of Shanghai Synchrotron Radiation facility and the researcher Huang Yaobo offered help in the process.

Original link：https://www.nature.com/articles/s41563-019-0494-1

Rewritten by: Dong Xiaoqian, edited by Cao Siyi, Shen Yuxi and Hu Sijia