Analogue of Rashba pseudo-spin-orbit coupling in photonic lattices by gauge field engineering

†These authors contributed equally to this work.The use of artificial gauge fields enables systems of uncharged particles to behave as if affected by external fields. Generated by geometry or external modulation, artificial gauge fields have been instrumental in demonstrating topological phenomena in many physical systems, including photonics, cold atoms and acoustic waves. Here, we demonstrate experimentally for the first time waveguiding by means of artificial gauge fields. To this end, we construct artificial gauge fields in a photonic waveguide array, by using waveguides with nontrivial trajectories. First, we show that tilting the waveguide arrays gives rise to gauge fields that are different in the core and the cladding, shifting their respective dispersion curves, and in turn confining the light to the core. In a more advanced setting, we demonstrate waveguiding in a medium with the same artificial gauge field and the same dispersion everywhere, but with a phase-shift in the gauge as the only difference between the core and the cladding. The phase-shifted sinusoidal trajectories of the waveguides give rise to waveguiding via bound states in the continuum. Creating waveguiding and bound states in the continuum by means of artificial gauge fields is relevant to a wide range of physical systems, ranging from photonics and microwaves to cold atoms and acoustics.Waveguiding -the ability to confine light in a region and guide it within a structure is a fundamental building block in many photonics applications. The basic structure of a waveguide consists of a core region where the light is confined and a cladding region within which the core is embedded. Standard waveguide structures rely on total internal reflection, and are made up of a high refractive index core surrounded by a low refractive index cladding, or on metallic pipes where the electromagnetic fields are completely forbidden from escaping [1]. Other schemes rely on photonic systems with bandgaps [2-6], coupled resonator arrays [7], grating-mediated waveguiding [8], Kapitza-effect arrangements [9] or exploit the vectorial spin-orbit interaction of light in an anisotropic medium [10]. In all of these, the core and the cladding are made from media with a different dispersion relation. Recently, a conceptually new waveguiding mechanics was proposed: a waveguide where the cladding and core region have the same dispersion curve, but the core's dispersion is shifted by virtue of an artificial gauge field [11].Gauge fields are a fundamental concept in physics, describing the basic interactions between charged particles. Neutral particles (such as photons) are thus decoupled from real gauge fields.However, by properly engineering a physical system, one can generate artificial gauge fields that would govern the effective dynamics of the neutral particles. That is, most often an artificial gauge field can be induced through the geometric design of the system or through some specific external modulation, such that the effective dynamics of the system behaves as...

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“…3c,d are calculated using a continuum Floquet eigensolver described in the supplementary material of Ref. [46].…”

Section: Methodsmentioning

confidence: 99%

Light guiding by artificial gauge fields

et al. 2019

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“…Coupling between a pseudospin or valley degree of freedom with the orbital motion of electrons in two-dimensional materials like graphene or monolayers of transition metal dichalcogenides have attracted a lot of interest too. Generation of synthetic gauge fields for ultracold gases [6,7], photonic [8], or mechanical [9] systems are being actively explored both theoretically and experimentally. While several interesting single particle phenomena are associated with the helicity in all these systems, introduction of interparticle interactions could lead to unexpected properties [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27].…”

Section: Introductionmentioning

confidence: 99%

Coupled spin-charge dynamics in helical Fermi liquids beyond the random phase approximation

Mir

Abedinpour

2017

Phys. Rev. B

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We consider a helical system of fermions with a generic spin (or pseudospin) orbit coupling. Using the equation of motion approach for the single-particle distribution functions, and a meanfield decoupling of the higher order distribution functions, we find a closed form for the charge and spin density fluctuations in terms of the charge and spin density linear response functions. Approximating the nonlocal exchange term with a Hubbard-like local-field factor, we obtain coupled spin and charge density response matrix beyond the random phase approximation, whose poles give the dispersion of four collective spin-charge modes. We apply our generic technique to the wellexplored two-dimensional system with Rashba spin-orbit coupling and illustrate how it gives results for the collective modes, Drude weight, and spin-Hall conductivity which are in very good agreement with the results obtained from other more sophisticated approaches.

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“…Here, ε is the quasi-energy; | j 〉 satisfies the static eigenvalue problem of e − i k ⋅ r Ae i k ⋅ r | j 〉 = ω j B 0 | j 〉 and therefore forms a complete basis of spatial modes. Similar approach has also been used in solving the Floquet eigenstates of periodic paraxial equations 23,24 . The detailed solution is presented in Supplementary Note 1 with discussions in Note 2.…”

Section: Resultsmentioning

confidence: 99%

Floquet Chern insulators of light

Addison

Jin

et al. 2019

Nat Commun

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Achieving topologically-protected robust transport in optical systems has recently been of great interest. Most studied topological photonic structures can be understood by solving the eigenvalue problem of Maxwell’s equations for static linear systems. Here, we extend topological phases into dynamically driven systems and achieve a Floquet Chern insulator of light in nonlinear photonic crystals (PhCs). Specifically, we start by presenting the Floquet eigenvalue problem in driven two-dimensional PhCs. We then define topological invariant associated with Floquet bands, and show that topological band gaps with non-zero Chern number can be opened by breaking time-reversal symmetry through the driving field. Finally, we numerically demonstrate the existence of chiral edge states at the interfaces between a Floquet Chern insulator and normal insulators, where the transport is non-reciprocal and uni-directional. Our work paves the way to further exploring topological phases in driven optical systems and their optoelectronic applications.

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Analogue of Rashba pseudo-spin-orbit coupling in photonic lattices by gauge field engineering

Cited by 27 publications

References 31 publications

Light guiding by artificial gauge fields

Light guiding by artificial gauge fields

Coupled spin-charge dynamics in helical Fermi liquids beyond the random phase approximation

Floquet Chern insulators of light

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