Circular Photocurrent in Weyl Semimetals with Mirror Symmetry

Abstract

We have studied theoretically the Weyl semimetals the point symmetry group of which has reflection planes and which contain equivalent valleys with opposite chiralities. These include the most frequently studied compounds, namely the transition metals monopnictides TaAs, NbAs, TaP, NbP, and also Bi1−xSbx alloys. The circular photogalvanic current, which inverts its direction under reversal of the light circular polarization, has been calculated for the light absorption under direct optical transitions near the Weyl points. In the studied materials, the total contribution of all the valleys to the photocurrent is nonzero only beyond the simple Weyl model, namely, if the effective electron Hamiltonian is extended to contain either an anisotropic spin-dependent linear contribution together with a spin-independent tilt or a spin-dependent contribution cubic in the electron wave vector k. With allowance for the tilt of the energy dispersion cone in a Weyl semimetal of the C4v symmetry, the photogalvanic current is expressed in terms of the components of the secondrank symmetric tensor that determines the energy spectrum of the carriers near the Weyl node; at low temperature, this contribution to the photocurrent is generated within a certain limited frequency range ∆. The photocurrent due to the cubic corrections, in the optical absorption region, is proportional to the light frequency squared and generated both inside and outside the ∆ window.

Nonlinear Absorption and Photocurrent in Weyl Semimetals

“…The linear-circular dichroism in absorption has been studied in both bulk semiconductors and quantum wells. [21][22][23][24] For linearly polarized light, we have from Equation (5), (8), and (12)…”

“…The results of this experiment have been explained by Ma et al by tilt of Weyl cones. This explanation is insufficient: the CPGE current is due to nonlinear in the momentum terms in the Hamiltonian rather than due to linear in momentum spin‐independent tilt terms, see previous studies for details.…”

“…Here are the Pauli matrices, is a symmetric 3 × 3 matrix, and is a transpose of the matrix . As a result, the energy and momentum relaxation times, and , should influence differently the saturation behavior: the energy relaxation removes the photocarriers from the resonance region marked by yellow and white stripes in Figure and resists to the saturation, whereas the elastic scattering causes the off‐diagonal electron‐hole decoherence but, on the other hand, conserves the carrier population in the resonant regions, the latter promoting the saturation. Accounting for not only inelastic but also elastic scattering of the photocarriers is a new move in the problem of interband saturation and is valid for systems with both trivial and nontrivial topologies.…”

Strain-induced circular photogalvanic current in Dirac semimetal Cd3As2 films epitaxied on a GaAs(111)B substrate

“…[35][36][37][38][39] In recent years, owing to the time-reversal or spatial inversion symmetry breaking, or both, there have been theoretical predictions and experimental observations for the CPGE in Weyl semimetals with a tilted Weyl cone, in which the asymmetric photoexcitation around the nodal points due to the Pauli blocking effect can generate a chirality-dependent photocurrent. [40][41][42][43][44][45][46][47] While the CPGE was theoretically predicted to vanish in an ideal Dirac system due to the symmetric photoexcitation about the Dirac point, [47][48][49] as a result of both the time-reversal and spatial inversion symmetries in DSMs. The CPGE generation in a 2D Dirac material such as graphene, however, has been reported to become visible by employing different substrate/interface designs and optical radiation configurations.…”

Light-field and spin-orbit-driven currents in van der Waals materials

“…The Berry curvature Ω n (k) of the bands diverges near the topological Weyl points giving rise to a plethora of predicted optoelectronic phenomena, including quantized photogalvanic effects, anomalous Hall effects [104,172], and selective coupling between photon and Weyl Fermion chirality [112,173]. For the point groups containing improper symmetry operations, in particular combinations of mirror and rotation symmetries, it has been shown theoretically that corrections to the minimal Weyl model, namely a tilt of the Weyl cone as well as second and third order terms, prevent cancellation of the photocurrent contributions from the Weyl cones of opposite chirality [106,107,174]. Along this line, so called type-II Weyl semimetals exhibit Weyl cones in the bulk that are tilted over one side, and within the class of TMDs MoTe 2 and WTe 2 were identified as potential candidates [175].…”