Spiraling Fermi arcs in Weyl materials

Abstract

In Weyl materials the valence and conduction electron bands touch at an even number of isolated points in the Brillouin zone. In the vicinity of these points the electron dispersion is linear and may be described by the massless Dirac equation. This results in nontrivial topology of Berry connection curvature. One of its consequences is the existence of peculiar surface electron states whose Fermi surfaces form arcs connecting projections of the Weyl points onto the surface plane. Band bending near the boundary of the crystal also produces surface states. We show that in Weyl materials band bending near the crystal surface gives rise to spiral structure of energy surfaces of arc states. The corresponding Fermi surface has the shape of a spiral that winds about the projection of the Weyl point onto the surface plane. The direction of the winding is determined by the helicity of the Weyl point and the sign of the band bending potential. For close valleys arc state morphology may be understood in terms of avoided crossing of oppositely winding spirals.Comment: 5 pages, 4 figues, v2 substantially modified, references update

First-principles mode-by-mode analysis for electron-phonon scattering channels and mean free path spectra in GaAs

“…Moreover, the phonon drag effect influences the Seebeck coefficient much more than the mobility [54]. On the other hand, the assumption of the equilibrium phonon distribution is used widely, in deriving phenomenological scattering models as well as in other first-principles-based efforts [35,46], and in general, this assumption has been working well. (iii) Renormalization of the electron energy due to the EPI is usually much smaller than the dominant energy scale in our study, which is the energy bandgap.…”

“…These techniques have since then been widely used to investigate EPI and to compute thermoelectric properties [37][38][39] and electron mean free path (MFP) spectra [39] in silicon as well as the electrical resistivity in graphene [40][41][42] under RTA. Such density-functional-theory-based (DFT-based) treatment can also be employed to compute electron mobility in weakly polar materials such as transition metal dichalcogenides [43][44][45][46] and perovskites [47,48], in which RTA still works due to the suppression of LO-phonon scatterings by strong dielectric screening. For strongly polar materials, like GaAs, the long-range information originating from polar-optical-phonon and piezoelectric interactions in e-ph coupling matrices are lost during the Wannier interpolation [35].…”

First-principles dynamics of electrons and phonons*

“…Transport properties such as electrical and thermal conductivities and thermoelectric coefficients can be computed either within the RTA or with numerical solutions of the BTE that explicitly include the scattering integral. The BTE can be solved beyond the RTA using iterative [65,66] and Monte Carlo approaches, among others.…”

Intrinsic Charge Transport in Stanene: Roles of Bucklings and Electron–Phonon Couplings

“…However, by implementing the Wannier-Fourier interpolation scheme, accurate electronic energies, phonon frequencies, and el-ph coupling matrix elements can be obtained with reasonable computational burden. Within this scheme, the electronic Hamiltonian [30] 2800 [38] D 3d ZA, TA [38] Silicene 2 × 10 5 [29] 2100, [36] 1200, [37] 750 [38] D 3d ZA, [36,38] TA [38] Graphene (2-3) × 10 5 , 3 × 10 5 , [24] 1 × 10 5 [27] (2-3) × 10 5 , 2 × 10 5 , [25] 1.5 × 10 5 [36] D 6h LA [25] α-Graphyne 3 × 10 4 [31] 1.6 × 10 4 [25] D 2h LA [25] Monolayer MoS 2 72-200 [32] 400, [36] 130, [37] 410, [50] 150, [52] 230 [51] D 3h LA, [37,50] LO 2 [50] Figure 5. The classification of nonplanarity for a) stanene and b) monolayer MoS 2 .…”

“…Buckling in the hexagonal honeycomb structure of stanene, originating from the sp 2 -sp 3 orbital hybridization, [47][48][49] can lead to remarkable difference from the planar structures such as graphene or graphynes, where huge intrinsic mobility ≈10 5 cm 2 V −1 s −1 has been predicted. [22] We note that the mobility in nonplanar structured monolayer MoS 2 was found to be 150-410 cm 2 V −1 s −1 [32,37,[50][51][52] and phosphorene to be 170-460 cm 2 V −1 s −1 . [53,54] It is thus intriguing to look at the contribution of each phonon mode to carrier transport and to compare with DPA for the buckled stanene layer.…”