spin degeneracy removal. Circular polarization resolved measurements revealed the
optical Rashba spin splitting in the dispersion of the emitted light from the inversion
The removal of the spin degeneracy in the
inversion asymmetric metasurface arises from
a spin-dependent Rashba correction resulting in the spin-orbit momentum-matching
condition. This selection rule, generated
from symmetry restrictions, is manifested
by combined contributions of structural and
local field lattices associated with differentiated unit cells of the inversion symmetric and
asymmetric structures, respectively.
By controlling the propagation direction of
excited electromagnetic waves, metasurfaces
with designed symmetries provide a route
for integrated spintronic-spinoptical nanocircuits. Optical spin as an additional degree
of freedom offers controlled manipulation of
spontaneous emission, absorption, scattering
and surface-wave excitation.
Photonic metasurfaces are metamaterials with reduced dimensionality composed of
engineered subwavelength-scale meta-atoms
enabling a custom-tailored electromagnetic
response of the medium. 1 These 2-D metastruc-tures are also at the forefront of the physical
enigma: What is the effect of surface symmetry
properties on light-matter interactions?
The Rashba effect is an illustration for a
perturbed interaction as a result of a symmetry
violation. 2 It is a manifestation of spin-orbit
interaction under broken inversion symmetry,
where the electron spin-degenerate bands split
into dispersions with oppositely spin-polarized
states. Like the role of the symmetry-breaking
potential gradient in the electronic Rashba
effect, the geometric gradient associated with
space-variant orientations of optical nanoan-tennas induces a spin-split dispersion, where
the photon spin corresponds to the circular
polarization helicity. 3
We reported on a novel class of metasurfaces—spinoptical metamaterials—which
give rise to a spin-controlled dispersion due
to the optical Rashba effect. 4 The inversion
asymmetry is obtained in artificial kagome
structures with anisotropic antenna configurations modeling the uniform and the
staggered chirality spin-folding modes in the
kagome antiferromagnet. 5 The geometrically
frustrated kagome lattice is a peculiar
platform since reordering local magnetic
moments transforms the lattice from one with
inversion symmetry to asymmetric.
We investigated the light-matter interaction
via optical mode measurement of the thermal
emission from the inversion symmetric and
asymmetric metasurfaces. The dispersion
relation of the symmetric structure exhibited
good agreement with the standard; however,
the dispersion of the asymmetric structure
exposes new modes, giving rise to an optical
(a,b) Inversion symmetric and asymmetric kagome metasurfaces with corresponding unit cells. Measured (c) and calculated (d) spin-polarized dispersions of
the inversion asymmetric structure, manifested by the Rashba spin splitting DkR;
s± stand for right and left circularly polarized light, respectively. (e) Spin-based
surface-wave multidirectional excitation via the optical Rashba effect offers control of propagation direction.
Nir Shitrit, Igor Yulevich,
Elhanan Maguid, Dror
Ozeri, Dekel Veksler,
Vladimir Kleiner and
Erez Hasman (
Technion, Haifa, Israel
1. A.V. Kildishev et al.
Science 339, 1232009
2. E.I. Rashba. Sov. Phys.
Solid State 2, 1109
3. N. Dahan et al. Phys.
Rev. Lett. 105, 136402
4. N. Shitrit et al. Science
340, 724 (2013).
5. D. Grohol et al. Nature
Mater. 4, 323 (2005).
A Novel Class of Metasurfaces
(b) (c) s+
– 1 –0.5 0 0.5 1