Reexamining Circular Dichroism in Photoemission From a Topological Insulator

Abstract

The orbital angular momentum (OAM) of electron states is an essential ingredient for topological and quantum geometric quantities in solids. For example, Dirac surface states with helical spin- and orbital-angular momenta are a hallmark of a 3D topological insulator. Angle-resolved photoemission spectroscopy (ARPES) with variable circular light polarization, known as circular dichroism (CD), has been assumed to be a direct probe of OAM and, by proxy, of the Berry curvature of electronic bands in energy- and momentum-space. Indeed, topological surface states have been shown to exhibit angle-dependent CD (CDAD), and more broadly, CD is often interpreted as evidence of spin-orbit coupling. Meanwhile, it is well-established that CD originates from the photoemission matrix elements, which can have extrinsic contributions related to the experimental geometry and the inherently broken inversion symmetry at the sample surface. Therefore, it is important to broadly examine CD-ARPES to determine the scenarios in which it provides a robust probe of intrinsic material physics. We performed CD-ARPES on the canonical topological insulator ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ over a wide range of incident photon energies. Not only do we observe angle-dependent CD in the surface states, as expected, but we also find CD of a similar magnitude in virtually all bulk bands. Since OAM is forbidden by inversion symmetry in the bulk, we conclude this originates from symmetry-breaking in the photoemission process. Comparison with theoretical calculations supports this view and suggests that $\text{hidden}$ OAM - localized to atomic sites within each unit cell - contributes significantly. Additional effects, including inter-atomic interference and final-state resonances, are responsible for the rapid variation of the CDAD signal with photon energy.

14 pages, 10 figures

References in corpus (14)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator class with spin-polarized single-Dirac-cone on the surface
• Spectral and Fermi surface properties from Wannier interpolation
• Observation of the orbital Hall effect in a light metal Ti
• Angle-resolved photoemission spectroscopy and its application to topological materials
• Dichroic f-sum rule and the orbital magnetization of crystals
• Selective probing of hidden spin-polarized states in inversion-symmetric bulk MoS2
• Measurements of the quantum geometric tensor in solids
• Polarization-Modulated Angle-Resolved Photoemission Spectroscopy: Towards Circular Dichroism without Circular Photons and Bloch Wavefunction Reconstruction
• Electronic structure and topology across $T_c$ in magnetic Weyl semimetal Co${}_3$Sn${}_2$S${}_2$
• The Huygens Principle of Angle-Resolved Photoemission
• Surface induced electronic Berry curvature in Berry curvature free bulk materials
• Geometry-induced spin-filtering in photoemission maps from WTe${}_2$ surface states
• Looking Beyond the Surface with Angle-Resolved Photoemission Spectroscopy

Cited by in corpus (2)

• Measurements of electronic band structure in CeCoGe${}_3$ by angle-resolved photoemission spectroscopy
• Circular dichroism in the photoelectron angular distribution of achiral molecules