Assessing Nontrivial Topology in Weyl Semimetals by Dichroic Photoemission

Towards Robust Dichroism in Angle-Resolved Photoemission

“…3 and the corresponding line-profile extraction in areas A-D show that both magnitude and sign are robust against variation of hv once the TR-LEED final state is used. The impressive reliability of the TR-LEED final state is also discussed elsewhere [9,25,26]. For the purpose of this work, it is sufficient to note that unlike the free-electron (FE) final state, TR-LEED final state "feels" the environment of the solid -its analytical form depends on the scattering environment of each scattering site of the sample.…”

“…This and the fact that its amplitude attenuates in the crystal are the main features that cannot possibly be captured by the FE final state description of the three-step model. From previous work [9], it immediately follows that the final state description itself is defining for the correct representation of LD and CD. Fig.…”

“…This implies that all of these observables are sensitive to the environment of the sample. This inherently local property of TRDAD may further contribute to the discussion of whether dichroism, in general, is sensitive to local "atomic" orbital angular momentum or to non-local orbital angular momentum manifolds, as understood by the "modern theory of polarization" [9,15]. The ℎ evolution of the signal with the TR-LEED final state is much less pronounced and can most likely be attributed to simpledispersion evolution.…”

“…At the end of the last century, it was shown [2] that ARPES spectral weight depends on the transition dipole matrix element between the initial Bloch wave and the final states. However, for simplicity, it is often assumed that the photoemission intensity is proportional to a one-particle spectral function of the initial states, and matrix element effects are neglected, even though they have proven to be pivotal, for example, when identifying topologically non-trivial materials [9] or for disentangling the origin of "waterfall" dispersion in high-temperature superconductors [10]. Matrix-element effects have been widely used to study the spin textures as well as the orbital textures [6,[11][12][13][14].…”

“…Matrix-element effects have been widely used to study the spin textures as well as the orbital textures [6,[11][12][13][14]. Namely, linear (LD) and circular dichroism (CD) [15][16][17][18][19] in the angular distribution in ARPES have been useful in assessing (and under certain assumptions even proportional to) orbital angular momentum or Berry curvature [9,15,16] -quantities crucial for the classification of topological insulators or Dirac and Weyl semimetals. The continuous efforts in the field eventually led to finding novel observables such as time-reversal dichroism in photoelectron angular distributions (TRDAD) [20], intrinsic linear dichroism in photoelectron angular distributions (iLDAD) [21] or complex Fourier dichroism [22].…”