Orbital-Driven Rashba Effect in a Binary Honeycomb Monolayer AgTe

Abstract

The Rashba effect is fundamental to the physics of two-dimensional electron systems and underlies a variety of spintronic phenomena. It has been proposed that the formation of Rashba-type spin splittings originates microscopically from the existence of orbital angular momentum (OAM) in the Bloch wave functions. Here, we present detailed experimental evidence for this OAM-based origin of the Rashba effect by angle-resolved photoemission (ARPES) and two-photon photoemission experiments for a monolayer AgTe on Ag(111). Using quantitative low-energy electron diffraction analysis, we determine the structural parameters and the stacking of the honeycomb overlayer with picometer precision. Based on an orbitalsymmetry analysis in ARPES and supported by first-principles calculations, we unequivocally relate the presence and absence of Rashba-type spin splittings in different bands of AgTe to the existence of OAM.

Momentum-space signatures of Berry flux monopoles in the Weyl semimetal TaAs

“…2a, b ). This indicates a scenario for the bulk states in TaAs, where the energy scale associated with ISB dominates over the one of SOC 32 , 33 , 36 (see also Supplementary Fig. 4 ).…”

“…For two-dimensional systems, the formation of OAM due to ISB has been shown to be the microscopic origin of SOC-induced spin splittings 36 , 47 . The present experiments establish a first instance where OAM-carrying bands are observed in a 3D bulk system.…”

Design and realization of topological Dirac fermions on a triangular lattice

“…For this reason, it represents an interesting complement to the common identification schemes based on the bulk-boundary correspondence. Its connection to the orbital angular momentum polarization in k-space can be experimentally unveiled by exploiting the coupling of circularly polarized light to the orbital magnetization and Berry curvature 26,27 . It also establishes fast early-stage material screening that is complementary to challenging quantum transport experiments and can become relevant to topology beyond solidstate physics, e.g., in optical lattices of ultra-cold gases 28 .…”

The Huygens Principle of Angle-Resolved Photoemission

“…Let us further study the angular dependence of linear dichroism in a system with similar out-and in plane orbital mixing: the 2D honeycomb monolayer AgTe/Ag(111) [20]. Its occupied low energy electronic structure is described by two distinct bands: band |α = sin φ k |p x − cos φ k |p y , of tangential orbital character with zero angular momentum; and Rashba split band |β = cos φ k |p x + sin φ k |p y + ik δ sp |sp z [27], of primarily radial orbital character, but with in-and out of plane orbital mixing δ sp ∼ 4.15 Å producing a rotating in plane orbital angular momentum L β = 2k δ sp (sin φ, cos φ, 0) that is governed -in contrast to BiAg 2 where SOC is decisive [14] -by inversion symmetry breaking at the surface [20,21].…”

“…This produces the oppositely oriented half moon structures in Fig. 3 (c,e) [21,22], whose angular intensity distributions are fitted to the model in panels (d,f), and provide the relevant cross-section ratios and Coulomb phase shifts annotated to the figure . Discussion.-Finally, let us discuss why -despite the preceding arguments -the PWA has served so well in describing ARPES intensity distributions, in particular also in orbital tomography [5]: The latter is typically applied to small organic molecules, whose main element carbon is light, Coulomb final state effects fade out quickly with increasing photon energy (η ∝ Z/k → 0, f / g ∼ const) and at least the angular part of the PWA holds. The investigated orbital character is almost entirely C 2p, spinorbit effects and OAM can thus be neglected and proper light polarization further limits orbital interference to a minimum -ideally even suppresses one of the two photo emission channels altogether.…”