# MRSEC: Layered magnetic topological semimetals and their unusual interlayer quantum transport

## Main Content

Recent discoveries of three dimensional topological semimetals have generated immense interests since they represent new topological states of quantum matters. In this talk, I will first introduce my group’s general research interests and then present our recent studies on topological semimetals [1-4], which are focused on Dirac/Weyl fermions generated by square lattices in layered compounds. I will report on our discoveries of new magnetic Dirac semimetals (Sr/Ba)_{1-y}Mn_{1-z}Sb_{2} [1,2]. In Sr_{1-y}Mn_{1-z}Sb_{2}, Dirac fermions are found to coexist with ferromagnetism, offering a rare opportunity to investigate the interplay between relativistic fermions and spontaneous time reversal symmetry breaking and explore a possible magnetic Weyl state [1]. Then I will discuss the unusual interlayer quantum transport behavior resulting from the zeroth Landau level (LL) mode observed in type-II Weyl semimetal YbMnBi_{2} [3]. The interlayer magnetoresistivity and Hall conductivity of this material were found to exhibit surprising angular dependences under high fields, which can be well fitted by a model which considers the interlayer quantum tunneling transport of the zeroth LL’s Weyl fermions. Our results shed light on the unusual role of zeroth LL mode in transport. Finally I will show our experimental evidences for the topological nodal line semimetal states found in ZrSiSe and ZrSiTe [4]. Since atomically thin crystals of these two materials are accessible via mechanical exfoliation, they raise the possibility of realizing the theoretically predicted 2D topological insulators.

References:

[1] Liu et al., Nature Materials, published online 2017, doi:10.1038/nmat4953.

[2] Liu et al., Sci. Rep. 6, 30525 (2016).

[3] Liu et al., arXiv 1608.05956, to appear in Nature Communications.

[4] Hu et al., Phys. Rev. Lett. 117, 016602 (2016) (Editor’s suggestion).