Prediction of Ideal Topological Semimetals with Triply Degenerate Points in NaCu3Te2 Family
Update: 2018-02-24 09:35:41      Author: yangjuan@csrc.ac.cn

As topological phase extends from insulators to semimetals, new quasiparticles analogous to elementary particles in high-energy physics emerge in these topological materials. Interestingly, the band theory has shown that the crystal symmetries in solids allow for the existence of other types of topological quasiparticle excitations even without high-energy counterparts. Especially, the triply degenerate points (TDPs), formed by the crossing of a double-degenerate band and a nondegenerate band, can be recognized as an intermediate phase between Weyl (double-degenerate) and Dirac (fourfold-degenerate) fermions. The TDP semimetals have been predicted to have some unique properties, e.g., Lifshitz transitions of Fermi surface, helical anomaly, large nonsaturating or negative magnetoresistance, and unconventional quantum Hall effects. One of the key problems for exploring the intrinsic properties of TDP fermions is the lack of ideal TDP semimetals, in which the TDPs around the Fermi level do not coexist with other quasiparticle bands. Therefore, it is of great importance to search for ideal host materials having only TDP fermions around Fermi level.

Recently, Bing Huang’s group in CSRC disclose an effective approach to search for ideal TDP semimetals via selective band crossing between antibonding s and bonding p orbitals along a line in the momentum space with C3v symmetry. Applying this approach, they have successfully identified the NaCu3Te2 family of compounds to be ideal TDP semimetals, where two and only two pairs of TDPs are located around the Fermi level. Moreover, they demonstrate a fundamental mechanism to modulate energy splitting between a pair of TDPs, and illustrate the intrinsic features of TDP Fermi arcs in these ideal TDP semimetals, as shown in Figure 1.

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FIG. 1: (a) Surface projected band and (b) Fermi surfaces with different EF for the (010) surface of a semi-infinite NaCu3Te2 system. Two circles in magnified Fermi surfaces denote the surface projections of two adjacent TDPs. (c) Evolution of Fermi arcs from Dirac to TDP to Weyl fermions.

 

References:

[1]   J. Wang, X. Sui, W. Shi, J. Pan, S. Zhang, F. Liu, S. -H. Wei, Q. Yan and B. Huang, Phys. Rev. Lett. 119, 256402 (2017).


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