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arXiv · 1712.03048

Experimental Observation of Dirac Nodal Links in Centrosymmetric Semimetal TiB$_2$

Zhonghao Liu·Rui Lou·Pengjie Guo·Qi Wang·Shanshan Sun·Chenghe Li·Setti Thirupathaiah·Alexander Fedorov·Dawei Shen·Kai Liu·Hechang Lei·Shancai Wang
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Abstract

The topological nodal-line semimetal state, serving as a fertile ground for various topological quantum phases, where a topological insulator, Dirac semimetal, or Weyl semimetal can be realized when the certain protecting symmetry is broken, has only been experimentally studied in very few materials. In contrast to discrete nodes, nodal lines with rich topological configurations can lead to more unusual transport phenomena. Utilizing angle-resolved photoemission spectroscopy and first-principles calculations, here, we provide compelling evidence of nodal-line fermions in centrosymmetric semimetal TiB$_2$ with a negligible spin-orbit coupling effect. With the band crossings just below the Fermi energy, two groups of Dirac nodal rings are clearly observed without any interference from other bands, one surrounding the Brillouin zone (BZ) corner in the horizontal mirror plane $σ_h$ and the other surrounding the BZ center in the vertical mirror plane $σ_v$. The linear dispersions forming Dirac nodal rings are as wide as 2 eV. We further observe that the two groups of nodal rings link together along the $Γ$-$K$ direction, composing a nodal-link configuration. The simple electronic structure with Dirac nodal links mainly constituting the Fermi surfaces suggests TiB$_2$ as a remarkable platform for studying and applying the novel physical properties related to nodal-line fermions.

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Zhonghao Liu, Rui Lou, Pengjie Guo, Qi Wang, Shanshan Sun, Chenghe Li, Setti Thirupathaiah, Alexander Fedorov, Dawei Shen, Kai Liu, Hechang Lei, Shancai Wang. 2018-08-18. Experimental Observation of Dirac Nodal Links in Centrosymmetric Semimetal TiB$_2$. https://doi.org/10.1103/physrevx.8.031044

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