Observation of a nodal chain with Dirac surface states in TiB2

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 k z = 0 and k x = 0 planes of the Brillouin zone in TiB 2 . The nodal rings connect with each other on the intersecting line Γ-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.

Magnetic and electronic properties of a topological nodal line semimetal candidate: HoSbTe

“…Numerous NLSMs have been theoretically predicted, such as CaAgX (X = P, As) [4], carbon allotropes [6], black phosphorus under pressure [7], antiperovskite Cu3PdN [8], and so on. However, only a few candidates have been verified by experiments [15,16]. Searching for new NLSMs is of great significance.…”

Quantum transport in topological semimetals under magnetic fields (II)

“…Nodal-line semimetals [65][66][67][68], in which the cross sections of conduction and valence bands are closed rings [ Fig. 3(a)] in momentum space [69][70][71][72], have the drumhead surface states, of which the direct evidence is still missing [73]. Recently, a new type of surface state called the floating band was discovered in the nodal-line semimetal ZrSiSe [74].…”

Topological nodal chains in optical lattices

“…Intriguingly, such gapless phase also possesses topological properties, such as quantized Berry phase and topologically protected drumhead surface states [3]. Nodal lines have numerous topological structures than nodal points, including nodal rings [4][5][6][7][8][9][10][11], nodal chains [12][13][14][15][16][17][18][19], nodal links [20][21][22][23][24] and nodal knots [25,26]. In particular, the nodal chains are formed by the nodal rings located on mutually orthogonal high-symmetry planes and touching each other at isolated points [12][13][14], which are the basics of generating nodal links and knots [14,19].…”

“…In particular, the nodal chains are formed by the nodal rings located on mutually orthogonal high-symmetry planes and touching each other at isolated points [12][13][14], which are the basics of generating nodal links and knots [14,19]. Thus, nodal chains have much richer topological properties waiting to be explored and observed, such as the unusual topological electromagnetic responses [12] and distinct topological surfaces states [14,17,18]. Experimental efforts recently have been devoted to searching materials with different nodal lines [27,28].…”