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arXiv · 1805.00827

Experimental observation of bulk nodal lines and electronic surface states in ZrB$_2$

Rui Lou·Pengjie Guo·Man Li·Qi Wang·Zhonghao Liu·Shanshan Sun·Chenghe Li·Xuchuan Wu·Zilu Wang·Zhe Sun·Dawei Shen·Yaobo Huang·Kai Liu·Zhong-Yi Lu·Hechang Lei·Hong Ding·Shancai Wang
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Abstract

Topological nodal-line semimetals are characterized by the line-contact bulk band crossings and the topological surface states. Breaking certain protecting symmetry turns this system into a Dirac semimetal or Weyl semimetal that hosts zero-dimensional isolated nodal points. Recent advances in band theory predicted a topological nodal-line semimetal state possessing a new type of nodal line in AlB$_2$-type diborides. Here, we report an experimental realization of nodal-line fermions and associated surface states near the Fermi energy in ZrB$_2$ by angle-resolved photoemission spectroscopy combined with first-principles calculations. The Dirac nodal lines in ZrB$_2$ wind into two groups of nodal rings, which are linked together along the $\Gamma$-$K$ direction. We further observe a distinct surface state connecting to each nodal line, indicative of the nontrivial topological nature of the bulk nodal lines. Therefore, our results provide convincing experimental evidence of the nodal-line semimetal states in ZrB$_2$ both in the bulk and on the surface, suggesting ZrB$_2$ as a remarkable platform for discovering unique phenomena induced by nodal-line fermions.

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Rui Lou, Pengjie Guo, Man Li, Qi Wang, Zhonghao Liu, Shanshan Sun, Chenghe Li, Xuchuan Wu, Zilu Wang, Zhe Sun, Dawei Shen, Yaobo Huang, Kai Liu, Zhong-Yi Lu, Hechang Lei, Hong Ding, Shancai Wang. 2018-05-02. Experimental observation of bulk nodal lines and electronic surface states in ZrB$_2$. https://doi.org/10.1038/s41535-018-0121-4

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