Spin-photonic Devices Research Articles

Full-zone optical spin injection in AlxGa1−xAs alloys

Abstract Full-zone optical spin injection in Al x Ga1−x As alloys is investigated by analyzing the degree of circular polarization (DCP) of luminescence in a quantum well architecture. Aluminium content in AlGaAs barrier layers is varied to explore both the direct- and indirect-bandgap regimes. For all the samples, experimental data are compared with a 30-band k .p model addressing the band structure of the alloy and the optical spin injection over the entire Brillouin zone. We observe circularly polarized luminescence arising from the spin generation either around Γ or the L valley. We interpret the specific shape of the DCP within a framework accounting for smaller electron spin relaxation at the higher k points of the X valley of the AlGaAs barrier layer. Moreover, it is found that the presence of strain plays a vital role in governing the magnitude and shape of the DCP spectra for near band-edge excitation while exciting spin-polarized carriers in the direct-bandgap AlGaAs. We believe that these findings are important for the realization of AlGaAs-based spin-photonic devices aiming at possible applications in quantum technology.

Highly switchable photonic spin hall effect in vanadium dioxide grating structure

The enhancement and manipulation of the photonic spin Hall effects are essential for the spin photonic applications. The emergence of the phase transition material, vanadium dioxide (VO2), presents a unique chance to explore its conductivity dependent optical properties. However, the explorations on the PSHEs in VO2 based microstructures are quite rare. Here, we report the enhanced and controllable reflected photonic spin Hall effects under the horizontal or vertical polarized wave by establishing the VO2 grating structure. It can be found that associated with the phase transition of VO2, its changed conductivity not only tunes the magnitude of the reflected spin shift but also changes its sign, which even results in a dramatic modulation of the reflected spin shift from the negative maximum value under the vertical polarized wave to the positive maximum value under the horizontal polarized wave at the specific wavelength. Such features can be attributed to the dramatic changes of the reflectances in the VO2 grating structure under different polarizations induced by the changed conductivity of VO2. Our results allow the actively alternative phase transition material based configurations capable of dramatic manipulation of the reflected spin shifts and it constitutes a significant step toward highly switchable spin photonic devices.

Graphene-Templated Achiral Hybrid Perovskite for Circularly Polarized Light Sensing.

This study points out the importance of the templating effect in hybrid organic-inorganic perovskite semiconductors grown on graphene. By combining two achiral materials, we report the formation of a chiral composite heterostructure with electronic band splitting. The effect is observed through circularly polarized light emission and detection in a graphene/α-CH(NH2)2PbI3 perovskite composite, at ambient temperature and without a magnetic field. We exploit the spin-charge conversion by introducing an unbalanced spin population through polarized light that gives rise to a spin photoconductive effect rationalized by Rashba-type coupling. The prepared composite heterostructure exhibits a circularly polarized photoluminescence anisotropy gCPL of ∼0.35 at ∼2.54 × 103 W cm-2 confocal power density of 532 nm excitation. A carefully engineered interface between the graphene and the perovskite thin film enhances the Rashba field and generates the built-in electric field responsible for photocurrent, yielding a photoresponsivity of ∼105 A W-1 under ∼0.08 μW cm-2 fluence of visible light photons. The maximum photocurrent anisotropy factor gph is ∼0.51 under ∼0.16 μW cm-2 irradiance. The work sheds light on the photophysical properties of graphene/perovskite composite heterostructures, finding them to be a promising candidate for developing miniaturized spin-photonic devices.

Giant and nonreciprocal photonic spin hall effect in asymmetric multilayered structure with bulk dirac semimetal

Abstract The nonreciprocal photonic spin Hall effect features the different reflected or transmitted spin shifts along two opposite incident wave propagating directions. However, previous investigations have always focused on the features of the photonic spin Hall effect along one incident wave propagating direction. How to achieve the nonreciprocal photonic spin Hall effect remains obscure. Here, we theoretically study the nonreciprocal photonic spin Hall effect in the asymmetric multilayered structure containing the Bulk Dirac Semimetal and other dielectric materials. It is found that under the horizontal polarization the maximum reflected spin shift value along one direction is up to around times of the incident wavelength at , but it is only times of the incident wavelength at along the other direction, which reflects the nonreciprocity of photonic spin Hall effect and thus can act as the photonic spin Hall diode. Such a sizeable directional difference between the reflected spin shifts along these two opposite directions originates from the fact that this structure loses its mirror symmetry and becomes an asymmetrical one, and the obvious difference in the values of the reflected spin shifts along the two directions can be attributed to the large difference in the values of . At the same time, we find that the Fermi energy of the Bulk Dirac Semimetal can effectively tune the spin shift along the backward direction, as well as the difference between the spin shifts for two different propagating directions, which causes the controllable nonreciprocal photonic spin Hall effect. Our results establish the alternative configuration for realizing the nonreciprocal photonic spin Hall effect, which facilitates the potential applications in the spin photonic devices.

Coexistence of large photonic spin Hall effect and high efficiency in a dielectric grating structure

Large reflected photonic spin Hall effects have been discovered in various nanostructures under either horizontal (H) or vertical (V) polarized wave. However, their corresponding reflectance efficiencies are always quite low and they generally cannot be enhanced simultaneously for both H and V polarized waves. How to achieve the large photonic spin Hall effects and high efficiencies for both H and V polarized waves at the same wavelength, which are essential for their efficient spin photonic applications, remains acute. To overcome this difficulty, we design one dimensional subwavelength dielectric grating structure and find that it supports the remarkable reflected photonic spin Hall effects under both H and V polarized waves at the same incident angle via well-designed geometrical parameters, which are also accompanied with high reflectances in the visible frequency. We also elucidate that the reflected spin shifts in this structure are related to the incident angle and thus can be engineered by it. Our findings about the dielectric grating structures contribute to an alternative approach to achieve the decent reflected spin shifts and efficiencies for both polarized waves, which enables the next-generation spin photonic devices, such as, precision metrology and quantum information processing.

Identification of magnetic state of transition metal dichalcogenides via photonic spin Hall effect

Monolayer transition metal dichalcogenides with magnetic exchange fields have been demonstrated to display the remarkable valley polarization and magnetooptical behaviors. However, the explorations of their photonic spin Hall effects are lacking. Here, we show that the reflected spin shift of monolayer transition metal dichalcogenides with magnetic exchange field is significantly different from that of the pristine one and it exhibits the distinctive dependence on the size of the magnetic exchange field. In addition, we can manipulate the reflected spin shift of monolayer transition metal dichalcogenides with the magnetic exchange field via its chemical potential. This work unravels the potential of the photonic spin Hall effect on identifying the magnetic state of monolayer transition metal dichalcogenides or the substrate, which might promote their potential applications in the spin photonic devices.

Tunable optical differential operation based on graphene at a telecommunication wavelength.

Optical differential operation based on the photonic spin Hall effect(SHE) has attracted extensive attention in image processing of edge detection, which has advantages of high speed, parallelism, and low power consumption. Here, we theoretically demonstrate tunable optical differential operation in a four-layered nanostructure of prism-graphene-air gap-substrate. It is shown that the spatial differentiation arises inherently from the photonic SHE. Furthermore, we find that the transverse spin-Hall shift induced by the photonic SHE changes dramatically near the Brewster angle with the incident angle increases at a telecommunication wavelength. Meanwhile, the Fermi energy of graphene and the thickness of the air gap can affect the transverse spin shift. Interestingly, we can easily adjust the Fermi energy of graphene in real time through external electrostatic field biasing, enabling fast edge imaging switching at a telecommunication wavelength. This may provide a potential way for future tunable spin-photonic devices, and open up more possible applications for artificial intelligence, such as target recognition, biomedical imaging, and edge detection.

Enhanced photonic spin Hall effect in Dirac semimetal metamaterial enabled by zero effective permittivity

With the recent discovery of three dimensional Dirac semimetals, their integrations with the optoelectronic devices allow the novel optical effects and functionalities. Here, we theoretically report the photonic spin Hall effect in a periodic structure, where three dimensional Dirac semimetals and the dielectric materials are assembled into the stack. The incident angle and frequency dependent spin shift spectrum reveals that the spin shifts of the transmitted wave in this structure emerge the obvious peaks and valleys for the horizontal polarized wave and their magnitudes and positions display a distinct dependence on the incident angle around the specific frequency. These observations originate from its zero value of the effective perpendicular permittivity and its greatly reduced transmission in the multilayered structure, whose mechanism is different from those in the previous works. Moreover, both the peaks and valleys of the transmitted spin shift are significantly sensitive to the Fermi energy of three dimensional Dirac semimetals, whose magnitudes and positions can be tuned by varying it. Our results highlight the vital role of three dimensional Dirac semimetals in their applications of the spin photonic devices and pave the way to explore the tunable photonic spin Hall effect by engineering their Fermi energies.

Asymmetric spin splitting of Laguerre-Gaussian beams in chiral PT-symmetric metamaterials.

We systematically study the spin Hall effect of light (SHEL) in chiral PT-symmetric metamaterials when Laguerre Gaussian beams (LG beams) are incident and discover that cross-polarization (rs p, rp s) and intrinsic orbital angular momentum (IOAM) result in an asymmetric splitting of left-spin circularly polarized (LCP) light and right-spin circularly polarized (RCP) light. Additionally, there are spin Hall shift peaks near |rpp | ≪ |rss | (rs s and rp p are Fresnel reflection coefficients). Altering the topological charge number ℓ, the chiral parameter κ, the dimensionless frequency M, and the incident angle θ may also influence the asymmetric spin splitting and displacement peak. We believe that this research will provide new ways to manipulate and enhance the asymmetric spin splitting of light and provide new applications for spin photonic devices.

Highly efficient spin-polarized beam splitter based on silicon Pancharatnam–Berry metasurface

The spin-polarized conversion and splitting of beam are highly important for photonic researches and applications. Although the photonic spin Hall effect (PSHE) realized by the Pancharatnam–Berry (PB) metasurface has shown unprecedented capabilities to control spin-polarized light, spin-polarized beam splitting metadevices suffer from the limitations of low-efficiency. Here, we present a highly efficient spin-polarized beam splitter (SPBS) based on PB metasurface comprising silicon nano elliptical cylinder (Si-NEC) arrays. Because of the electromagnetic multipole resonance inside the designed Si-NECs, the PB metasurface can achieve high transmittance and enhanced PSHE. Therefore, the SPBS based on the PB metasurface can achieve a high spin conversion efficiency of nearly 100%, while ensuring a transmittance of 87% at 622 nm wavelength. It can also maintain a good working effect within the bandwidth of 600–660 nm. Furthermore, by introducing spatial shift between the two reverse Si-NEC arrays, the SPBS can also be used to realize 45° polarization rotation of an incident linearly polarized light, avoiding the input polarization angle dependence. Our design may have potential applications in high-performance and broadband spin-photonic devices.

Influence of interface states on built-in electric field and diamagnetic-Landau energy shifts in asymmetric modulation-doped InGaAs/GaAs QWs

The impact of interface defect states on the recombination and transport properties of charges in asymmetric modulation-doped InGaAs/GaAs quantum wells (QWs) is investigated. Three sets of high-mobility InGaAs QW structures are systematically designed and grown by the metal-organic vapor phase epitaxy technique to probe the effect of carrier localization on the electro-optical processes. In these structures, a built-in electric field drifts electrons and holes towards the opposite hetero-junctions of the QW, where their capture/recapture processes are assessed by temperature-dependent photoreflectance, photoluminescence, and photoconductivity measurements. The strength of the electric field in the structures is estimated from the Franz Keldysh oscillations observed in the photoreflectance spectra. The effects of the charge carrier localization at the interfaces lead to a reduction of the net electric field at a low temperature. Given this, the magnetic field is used to re-distribute the charge carriers and help in suppressing the effect of interface defect states, which results in a simultaneous increase in luminescence and photoconductivity signals. The in-plane confinement of charge carriers in QW by the applied magnetic field is therefore used to compensate the localization effects caused due to the built-in electric field. Subsequently, it is proposed that under the presence of large interface defect states, a magnetic field-driven diamagnetic-Landau shift can be used to estimate the fundamental parameters of charge carriers from the magneto-photoconductivity spectra instead of magneto-photoluminescence spectra. The present investigation would be beneficial for the development of high mobility optoelectronic and spin photonic devices in the field of nano-technology.

Electric field induced spin resolved graphene p–n junctions on magnetic Janus VSeTe monolayer

Graphene based p–n junctions exhibit intriguing and distinctive electronic properties, making them promising candidates for spintronic and spin photonic devices. While the attendant realization of magnetized graphene p–n junctions is highly desirable. Using first-principles calculations, we show that in the presence of magnetic proximity coupling effect of graphene supported on Te-termination magnetic Janus VSeTe monolayer (VSeTe/G), the graphene is readily spin-polarized and the Dirac bands near Fermi level keep intact. More interestingly, the external electric field (E ex) could significantly influence the bands of the spin down channel near Fermi level, due to the dominant electronic Coulomb screening effect. When the E ex exceeds 0.35 eV Å−1 with opposite direction to intrinsic dipole moment, the VSeTe/G heterostructure would turn into n type doping from the initial light p type doping in the spin down channel. However, those of the spin up channel in the vicinity of Fermi level are inert and still preserve initial p type against external electric field. In terms of such distinctive differences between the Dirac bands in the spin up and spin down channels, we propose a featured spin resolved graphene p–n junctions on magnetic Janus VSeTe by applying appropriate external electric field. Our findings are generally applicable to other similar magnetic Janus systems (i.e. graphene/FeICl) and might provide a feasible strategy to realize stable spin resolved graphene p–n junctions extendedly.

Signature of linear-in- k Dresselhaus splitting in the spin relaxation of X -valley electrons in indirect band gap AlGaAs

GaAs/AlGaAs quantum well (QW) system is utilized to investigate the electron spin relaxation in the satellite X-valley of indirect band gap Al0.63Ga0.37As epitaxial layers through polarization resolved photo-luminescence excitation spectroscopy. Solving the rate equations, steady state electronic distribution in various valleys of AlxGa1-xAs is estimated against continues photo carrier generation and an expression for the degree of circular polarization (DCP) of photoluminescence coming from the adjacent quantum well (QW) is derived. Amalgamating the experimental results with analytical expressions, the X-valley electron spin relaxation time ({\tau}_S^X) is determined to be 2.7 +/- 0.1 ps at 10 K. To crosscheck its validity, theoretical calculations are performed based on Density Functional Theory within the framework of the projector augmented wave method, which support the experimental result quite well. Further, temperature dependence of {\tau}_S^X is studied over 10-80 K range, which is explained by considering the intra-valley scattering of carriers in the X-valley of indirect band gap AlGaAs barrier layer. It is learnt that the strain induced modification of band structure lifts the degeneracy in X-valley, which dominates the electron spin relaxation beyond 50 K. Furthermore, the DCP spectra of hot electrons in indirect band gap AlGaAs layers is found to be significantly different compared to that of direct bandgap AlGaAs. It is understood as a consequence of linear k dependent Dresselhaus spin splitting and faster energy relaxation procedure in the X-valley. Findings of this work could provide a new horizon for the realization of next generation spin-photonic devices which are less sensitive to Joule heating.

Nonreciprocal photonic spin Hall effect of magnetic Weyl semimetals

Magnetic Weyl semimetals allow the unique opportunities for the realizations of nonreciprocal optical properties, thermal radiation, and anomalous photon thermal Hall effect without the requirement of an external magnetic field. Here, we theoretically investigate the photonic spin Hall effect in the magnetic Weyl semimetal-based multilayered structure and demonstrate that this effect is nontrivial and nonreciprocal. Its induced nontrivial photonic spin Hall effect originates from the large differences between the reflectances under different polarized waves. In addition, the generation of this kind of nonreciprocal photonic spin Hall effect is guaranteed by the simultaneously broken space inversion symmetry and time reversal symmetry of this specific structure. Specially, the responses of nonreciprocal photonic spin Hall effect can sustain within a certain range of incident angle and it can be effectively manipulated by varying the Fermi energy of magnetic Weyl semimetals. Our work expands the fields of the photonic spin Hall effects and suggests magnetic Weyl semimetals potential candidates in the next-generation nonreciprocal spin photonic devices.

High-performance photonic spin Hall effect in anisotropic epsilon-near-zero metamaterials.

A high-performance photonic spin Hall effect is demonstrated in an anisotropic epsilon-near-zero (ENZ) metamaterial based on the wave-vector-varying Pancharatnam-Berry phase. The giant out-of-plane anisotropy of ENZ metamaterial induces strong spin-orbit coupling. With a small incident angle, photons with opposite spins move along opposite transverse directions gradually. After transmitting through a submicrometer thick ENZ metamaterial, the spin photons are fully separated with a spin separation of 2.7 times beam waist and transmittance of 70.1%, allowing a figure of merit F up to 1.9. A practical ENZ metamaterial consisting of an Ag nanorod array is proposed, whose figure of merit is still up to 0.006. This high-performance photonic spin Hall effect provides an integrated and practical way for the development of spin-photonic devices.

Tunable and enhanced photonic spin Hall effect of a superconductor film

Due to the small sizes of photonic spin Hall effect, its enhancement and manipulation are of significance for the development of spin photonic devices. In this work, we have investigated the photonic spin Hall effect of a superconductor slab by using transfer matrix method and angular spectrum theory. It is found that the maximum positive spin shift can be achieved in a superconductor slab with the appropriate thickness, whose magnitude is 14.8 λ at the temperature of 91 K when the beam waist is 30 λ. The magnitudes of the spin shift peak and valley are decided by the combination of Re[rs/rp] and |rp′|/|rp|. In addition, the magnitudes and the positions of the peak and valley in the spectrum of spin shift are sensitive to the temperature of the superconductor, which indicates an alternative way to control the photonic spin Hall effect. Our findings provide the possibility for realizing the controllable photonic spin Hall effect by virtue of the superconductors, which promises their potential applications in spin photonic devices.

Lateral-Type Spin-Photonics Devices: Development and Applications.

Spin-photonic devices, represented by spin-polarized light emitting diodes and spin-polarized photodiodes, have great potential for practical use in circularly polarized light (CPL) applications. Focusing on the lateral-type spin-photonic devices that can exchange CPL through their side facets, this review describes their functions in practical CPL applications in terms of: (1) Compactness and integrability, (2) stand-alone (monolithic) nature, (3) room temperature operation, (4) emission with high circular polarization, (5) polarization controllability, and (6) CPL detection. Furthermore, it introduces proposed CPL applications in a wide variety of fields and describes the application of these devices in biological diagnosis using CPL scattering. Finally, it discusses the current state of spin-photonic devices and their applications and future prospects.

Controlling photonic spin Hall effect based on tunable surface plasmon resonance with an N−type coherent medium

We propose a scheme to control the spin Hall effect (SHE) of light reflected from a Kretschmann configuration containing an N-type coherent atomic medium. Owing to the excitation of surface plasmon resonance (SPR), enhanced spin splitting occurs in the reflection dip for TM-polarized incident light. The magnitude and sign of the transverse shifts of spin components depend on the system internal damping which is closely related to the absorption coefficient of atoms. There is an optimal absorption around which the spin components undergo large transverse displacements. We also show that the direction of the photonic spin accumulations can be switched between positive and negative values by adjusting the system parameters. In addition, the resonance angle of SPR varies linearly with the refractivity of the medium. We can therefore coherently control the peak position of the transverse shift. Compared to the conventional SPR-based systems, the proposed scheme provides a more flexible pathway for manipulating and enhancing the SHE of light without changing the structure. This tunable SHE may find applications in spin photonic devices.

Recent Progress of Spin-photonic Devices and its Applications

Recent Progress of Spin-photonic Devices and its Applications

All-optical switchable terahertz spin-photonic devices based on vanadium dioxide integrated metasurfaces

Metasurfaces based on Pancharatnam–Berry (P–B) phase can achieve strong spin angular momentum (SAM) to orbital angular momentum (OAM) conversion of light, which provides a new degree of freedom for light control and opens up a new way for the applications of metasurfaces in classical and quantum optics. With the development of high-speed, large-capacity information transmission and high-definition imaging, demand for multifunctional and tunable P–B phase metasurfaces increases. Here, we propose three switchable terahertz spin-photonic devices based on P–B phase metasurfaces for focusing (divergence), splitting and vortex generation of terahertz beams. Based on photo-induced insulator–metal phase transition of the vanadium dioxide (VO2) islands in reflective hybrid resonators, switching of the devices function between on- and off-state is obtained, and the amplitude switching efficiency is as high as 90%. This work provides new ideas for the design of active terahertz devices and facilitates the applications of terahertz spin-photonic devices based on metasurfaces.