Erratum: Berry curvature and orbital angular momentum of electrons in angle-resolved photoemission spectroscopy [Phys. Rev. B 
91
, 245133 (2015)]

Abstract Orbital angular momentum (OAM) plays a central role in regulating the magnetic state of electrons in non-periodic systems such as atoms and molecules. In solids, on the other hand, OAM is usually quenched by the crystal field, and thus, has a negligible effect on magnetisation. Accordingly, it is generally neglected in discussions around band topology such as Berry curvature (BC) and intrinsic anomalous Hall conductivity (AHC). Here, we present a theoretical framework demonstrating that crystalline OAM can be directionally unquenched in transition metal oxides via energetic proximity of the conducting d electrons to the local magnetic moments. We show that this leads to `composite' Fermi-pockets with topologically non-trivial OAM textures. This enables a giant Berry curvature with an intrinsic non-monotonic AHC, even in collinearly-ordered spin states. We use this model to explain the origin of the giant AHC observed in the forced-ferromagnetic state of EuTiO3 and propose it as a prototype for OAM driven AHC.

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Chiral fermion reversal in chiral crystals

Nature Communications ◽

10.1038/s41467-019-13435-4 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 11

Author(s):

Hang Li ◽

Sheng Xu ◽

Zhi-Cheng Rao ◽

Li-Qin Zhou ◽

Zhi-Jun Wang ◽

...

Keyword(s):

Electronic Structures ◽

Momentum Space ◽

Real Space ◽

Photoemission Spectroscopy ◽

Helical Surface ◽

Berry Curvature ◽

Angle Resolved Photoemission Spectroscopy ◽

Fermi Arcs ◽

Chiral Crystals ◽

Weyl Fermions

AbstractIn materials chiral fermions such as Weyl fermions are characterized by nonzero chiral charges, which are singular points of Berry curvature in momentum space. Recently, new types of chiral fermions beyond Weyl fermions have been discovered in structurally chiral crystals CoSi, RhSi and PtAl. Here, we have synthesized RhSn single crystals, which have opposite structural chirality to the CoSi crystals we previously studied. Using angle-resolved photoemission spectroscopy, we show that the bulk electronic structures of RhSn are consistent with the band calculations and observe evident surface Fermi arcs and helical surface bands, confirming the existence of chiral fermions in RhSn. It is noteworthy that the helical surface bands of the RhSn and CoSi crystals have opposite handedness, meaning that the chiral fermions are reversed in the crystals of opposite structural chirality. Our discovery establishes a direct connection between chiral fermions in momentum space and chiral lattices in real space.

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Studying local Berry curvature in 2H-WSe2 by circular dichroism photoemission utilizing crystal mirror plane

Scientific Reports ◽

10.1038/s41598-020-79672-6 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Soohyun Cho ◽

Jin-Hong Park ◽

Soonsang Huh ◽

Jisook Hong ◽

Wonshik Kyung ◽

...

Keyword(s):

Circular Dichroism ◽

Atomic Orbital ◽

Photoemission Spectroscopy ◽

Mirror Plane ◽

Experimental Procedure ◽

Berry Curvature ◽

Angle Resolved Photoemission Spectroscopy ◽

Experimental Constraint ◽

Arpes Data ◽

Circular Dichroïsm

AbstractIt was recently reported that circular dichroism in angle-resolved photoemission spectroscopy (CD-ARPES) can be used to observe the Berry curvature in 2H-WSe2 (Cho et al. in Phys Rev Lett 121:186401, 2018). In that study, the mirror plane of the experiment was intentionally set to be perpendicular to the crystal mirror plane, such that the Berry curvature becomes a symmetric function about the experimental mirror plane. In the present study, we performed CD-ARPES on 2H-WSe2 with the crystal mirror plane taken as the experimental mirror plane. Within such an experimental constraint, two experimental geometries are possible for CD-ARPES. The Berry curvature distributions for the two geometries are expected to be antisymmetric about the experimental mirror plane and exactly opposite to each other. Our experimental CD intensities taken with the two geometries were found to be almost opposite near the corners of the 2D projected hexagonal Brillouin zone (BZ) and were almost identical near the center of the BZ. This observation is well explained by taking the Berry curvature or the atomic orbital angular momentum (OAM) into account. The Berry curvature (or OAM) contribution to the CD intensities can be successfully extracted through a comparison of the CD-ARPES data for the two experimental geometries. Thus, the CD-ARPES experimental procedure described provides a method for mapping Berry curvature in the momentum space of topological materials, such as Weyl semimetals.

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