Observation of a nodal chain with Dirac surface states in TiB2

Authors :: Yi, C. -J.
Lv, B. Q.
Wu, Q. S.
Fu, B. -B.
Gao, X.
Yang, M.
Peng, X. -L.
Li, M.
Huang, Y. -B.
Richard, P.
Shi, M.
Li, G.
Yazyev, Oleg V.
Shi, Y. -G.
Qian, T.
Ding, H.
Source :: Phys. Rev. B 97, 201107(R) (2018)
Publication Year :: 2018
Abstract: Topological nodal-line semimetals (TNLSMs) are characterized by symmetry-protected band crossings extending along one-dimensional lines in momentum space. The nodal lines exhibit a variety of possible configurations, such as nodal ring, nodal link, nodal chain, and nodal knot. Here, using angle-resolved photoemission spectroscopy, we observe nodal rings in the orthogonal kz = 0 and kx = 0 planes of the Brillouin zone in TiB2. The nodal rings connect with each other on the intersecting line {\Gamma}-K of the orthogonal planes, forming a remarkable nodal-chain structure. Furthermore, we observe surface states (SSs) on the (001) cleaved surface, which are consistent with the calculated SSs considering the contribution from both Ti and B terminations. The calculated SSs have novel Dirac-cone-like band structures, which are distinct from the usual drumhead SSs with a single flat band proposed in other TNLSMs.<br />Comment: 15 pages, 4 figures