New type of hybrid nodal line semimetal in Be₂Si

Abstract

Following Dirac and Weyl semimetals, nodal line semimetals represent a new type of topological semimetal and attracted extensive interest in modern condensed matter physics. Recently, a kind of hybrid nodal lines have been proposed (Zhang et al 2018 Phys.Rev. B 97 125143) and it mainly come from anisotropy interaction. Based on the first-principle calculations and k·p model, we predict a cubic Be 2 Si with topological nontrivial electronic states exhibiting fascinating type-I and type-II hybrid nodal line around Fermi level. Unexpectedly the low energy electronic states of Be 2 Si are isotropy in k x and k y directions and a new effective model has been proposed for the appearance of this new type hybrid nodal line. The four-fold degenerated type-I and type-II nodal points in the hybrid nodal lines along the high symmetry lines of Γ-K and Γ-X are protected by mirror reflection, time reversal and space inversion symmetry. The spin-orbit coupling effect only induces slight band gap in the hybrid nodal lines in Be 2 Si whose nontrivial nature remains. Moreover, the nontrivial hybrid nodal lines in Be 2 Si are robust to external strain. The results in present work indicate that Be 2 Si are promising candidates for future experimental studies of nontrivial topological semimetals and an excellent platform to study the interaction between the two types Dirac fermions.

Perovskite-type YRh$_{3}$B with multiple types of nodal point and nodal line states

“…Moreover, from Fig. 8(b), it can be noted that the Γ-nodal ring in R1 is type I and the Γ-nodal ring in R2 is a hybrid type [68,69]. A criticaltype BCP to type I BCP transition can be observed from paths Γ-X to Γ-M in R2.…”

Ferromagnetic hybrid nodal loop and switchable type-I and type-II Weyl fermions in two-dimension

“…First, our most important finding in this work is that, we proposes the first example of hybrid nodal loop both in 2D materials and in magnetic system. To date, hybrid nodal loop is only proposed in a few 3D materials including tetragonal Ca 2 As [49], Li 2 BaSi [50], CsCl-type YCd [51], CrP 2 O 7 compound [52] and binary Be 2 Si [53], and has been identified in 2D materials yet. Moreover, these examples are almost non-magnetic materials, i.e., their nodal loops are contributed by electron states from both spin channels.…”

“…Benefiting from the coexistence of type-I and type-II band crossings, hybrid nodal loop can exhibit quite unique magnetic responses such as zero-field magnetic breakdown and Klein tunneling [49]. Hybrid nodal loop has been predicted in a few nonmagnetic (NM) bulk materials [49][50][51][52][53], but has not been identified in 2D or magnetic system yet.…”

Tunneling phase diagrams in anisotropic Multi-Weyl semimetals

“…The characteristic feature of semimetals is that they are gapless but have neglibible overlap between conduction and valence band. That is, their conduction and valence bands touch at isolated points, nodal lines or nodal surfaces [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Most exciting are cases, where these band crossings are topologically protected.…”