Anisotropic Dirac electronic structures ofAMnBi2(A=Sr,Ca)

Abstract

Low-energy electronic structures in AMnBi 2 (A=alkaline earths) are investigated using a first-principles calculation and a tight binding method. An anisotropic Dirac dispersion is induced by the checkerboard arrangement of A atoms above and below the Bi square net in AMnBi 2 . SrMnBi 2 and CaMnBi 2 have a different kind of Dirac dispersion due to the different stacking of nearby A layers, where each Sr (Ca) of one side appears at the coincident (staggered) xy position of the same element at the other side. Using the tight binding analysis, we reveal the chirality of the anisotropic Dirac electrons as well as the sizable spin-orbit coupling effect in the Bi square net. We suggest that the Bi square net provides a platform for the interplay between anisotropic Dirac electrons and the neighboring environment such as magnetism and structural changes.

Revealing the ultrafast light-to-matter energy conversion before heat diffusion in a layered Dirac semimetal

“…The cone has a summit at 0.35Å −1 away from Γ . The observed band nicely matched to the calculated LDC [46] which has anisotropic band velocities of 2.1 and 2.8 eVÅ in the Γ and M sides, respectively, and that is gapped from the upper Dirac cone (UDC) due to spin-orbit interaction; see Fig. 1(e).…”

Valley-Polarized Interlayer Conduction of Anisotropic Dirac Fermions inSrMnBi2

“…A broad maximum at T ∼ 200 K in ρ c ðTÞ resembles the typical behavior of quasi-2D systems showing a crossover from high-T incoherent to low-T coherent conduction [19,20]. Previous studies [11,12] revealed quasi-2D open FSs and a 3D closed FS with a donut shape in the Brillouin zone [ Fig. 1(a)], which are denoted as α and β FSs, respectively [21].…”

“…On the other hand, much slower dispersion normal to the Γ-M line is due to hybridization between Sr d xz;yz and Bi p x;y orbitals. The resulting anisotropy in the Fermi velocity of the Dirac cone reaches ∼5-10 [11,12,15], much larger than found in other Dirac systems [16,17]. Therefore, SrMnBi 2 provides a model system with anisotropic quasi-2D Dirac valleys, which can host the valley-polarized current under a magnetic field.…”

“…Among various Dirac materials, SrMnBi 2 is of particular interest because of its highly anisotropic quasitwo-dimensional (2D) Fermi surface (FS) [11][12][13][14][15]. In SrMnBi 2 , four valley-degenerate Dirac cones are on the Γ-M symmetry lines in the Brillouin zone, which has distinct energy dispersion against the momentum direction.…”

Phase stability and large in-plane resistivity anisotropy in the 112-type iron-based superconductor Ca1−xLaxFeAs2

“…[6], where it was pointed out that this structure would support metallic spacer layers which could aid in elucidating the mechanism for high temperature superconductivity. Attempts to synthesize iron pnictide compounds in this structure were not originally successful, but new Mn based materials in this structure were found [7,8] and it was observed theoretically [7] and experimentally [8][9][10][11] that the spacer layers exhibit Dirac cones [12]. Recently, Fe superconductors in the 112 structure were synthesized, (Ca,Pr)FeAs 2 [13], and Ca 1−x La x FeAs 2 [14].…”