Spin Selective Transmission Research Articles

Silver induced chirality controlled spin filtration observed in ss-DNA functionalized with MoS2.

Chiral molecules can exhibit strong spin-orbit coupling, which can result in a large spin polarization. This is due to the fact that the energy levels of the electrons in a chiral molecule are strongly influenced by the chiral structure of the molecule, which can result in the separation of the energy levels for electrons with different spin orientations. We report a controlled spin-selective transmission of electrons through 20 base-paired poly-cytosine molecules functionalized with MoS2 flakes on ITO glass via the quantum mechanical tunneling effect. A reversion in spin polarization was observed after the silver ions interact with poly-cytosine due to the strong coordination of Ag(I) with cytosine-cytosine (C-C) mismatches, indicating the formation of duplex structural motifs, as confirmed by the circular dichroism spectroscopy at room temperature. Manipulating the spin of an electron through such a small molecule merely controlled by special cations could pave the way for major advances in spin-independent charge transport, advanced bioanalytical system design, and related applications.

Localized spin-selective interference assisted broadband tunable chirality with diatomic all-dielectric metasurfaces

Chiral metasurfaces with spin-selective properties have shown an unprecedented ability to modulate optical properties on the subwavelength scale. Alternatively, the simultaneous implementation of broadband tunable chiral response and wavefront manipulation on minimalistically constructed monolayer metasurfaces can lead to a plethora of applications such as optical converter diodes, chiral imaging, and sensing. Benefiting from a localized interference between two pairs of achiral meta-atoms whose optical behavior is similar to that of a half-wave plate (HWP), we theoretically provide a design strategy for constructing meta-molecules for asymmetric transmission (AT) parameters using interference mechanisms, each of which achieves a specific modulation function in the terahertz (THz) band. Localized interference effects with polarization-selective properties permit the incident circular polarization to be transformed into its orthogonal polarization mode. Benefiting from spin-selective transmission, the proposed metasurface simultaneously implements polarization filtering and wavefront manipulation with the assistance of a geometric phase mechanism. Not only that, chiral imaging schemes are also evaluated under such a design mechanism. As a result, this generalized assembly scheme can not only be extended to arbitrary working bands, but also find a variety of applications in photodetectors.

Multi-band spin-selective transmission and reflection in bi-layer T-shaped metamaterial

The control of the spin angular momentum of light plays an irreplaceable role in modern photon applications. In this work, we proposed a chiral metamaterial based on a bi-layer T-shaped structure. When circularly polarized light is incident along the normal direction (-z), the spin-selective transmissions and reflections occur in the mid-infrared frequency, which results in different transmittance and reflectance in quad-band frequencies. Here, the difference in transmittance (ΔT) values are 0.5, 0.4, 0.5, and 0.7, respectively. And the difference in reflectance (ΔR) reaches up to 0.4, 0.3, 0.4, and 0.5, respectively. Due to the chirality of the structure, the resulting circular dichroism (CD) is close to 0.2. In addition, the frequency and amplitude of the quad-band spin selections can be easily manipulated by rotating the rotation angle θ. Finally, we found that the similar spin-selective transmission and reflection can be achieved in Gigahertz (GHz) and Terahertz (THz) wavebands. The metamaterial might promote the application and development of versatile photonic devices.

Chiral metasurface zone plate for transmission-reflection focusing of circularly polarized terahertz waves.

The properties of traditional Fresnel zone plates have been greatly enhanced by metasurfaces, which allow the control of polarization, orbital angular momentum, or other parameters on the basis of focusing. In this Letter, a new, to the best of our knowledge, method for circularly polarized wave manipulation based on a zone plate is proposed. Chiral meta-atoms and binary geometric phase are used for the simultaneous focusing of reflected and transmitted terahertz waves. The silicon-based dielectric chiral units, which show great performance of spin-selective transmission near 0.54 THz, separate the orthogonal circularly polarized components. A binary Pancharatnam-Berry (P-B) phase gradient is obtained by rotating the unit 90 degrees, then the phase zone plate can be easily designed. The simulation results show that the proposed chiral metasurface zone plate has the function of reflection-transmission separation and focusing for the circularly polarized terahertz waves. In addition, we also demonstrate the possibility of using a 1064-nm continuous infrared laser to adjust the intensity of our devices, based on photo-generated carriers in silicon. The design principle of the chiral metasurface zone plates can be extended to other wavelengths, providing new ideas for the regulation of circularly polarized light.

Multifunctional Metasurfaces Enabled by Multifold Geometric Phase Interference.

Geometric phase is frequently used in artificially designed metasurfaces; it is typically used only once in reported works, leading to conjugate responses of two spins. Supercells containing multiple nanoantennas can break this limitation by introducing more degrees of freedom to generate new modulation capabilities. Here, we provide a method for constructing supercells for geometric phases using triple rotations, each of which achieves a specific modulation function. The physical meaning of each rotation is revealed by stepwise superposition. Based on this idea, spin-selective holography, nanoprinting, and their hybrid displays are demonstrated. As a typical application, we have designed a metalens that enables spin-selective transmission, allowing for high-quality imaging with only one spin state, which can serve as a plug-and-play chiral detection device. Finally, we analyzed how the size of supercells and the phase distribution inside it can affect the higher order diffraction, which may help in designing supercells for different scenarios.

Hybrid bilayer plasmonic metasurfaces with intrinsic chiral optical responses

Plasmonic metasurfaces with giant chiral optical responses are good candidates for chirality study and application, which are usually composed of few-layer or three-dimensional nanostructures. Here, we demonstrate that hybrid bilayer plasmonic metasurfaces simply fabricated via a facile one-step nanofabrication process are good candidates for the realization of intrinsic chiral optical responses and spin-selective transmission. We prove that the intrinsic chiral optical response of the proposed metasurface, which can be easily manipulated, is attributed to the spin-selective collective interference of locally enhanced electric fields caused by the strong interlayer coupling. We further experimentally prove the advantages of fabricated hybrid bilayer plasmonic metasurfaces for optical encryption. With the advantages of compact design, chiral optical response easy to control and lower fabrication demand, the proposed metasurfaces can further expand the applications of chiral plasmonic nanostructures in the area of spin nanophotonics, nonlinear optics, and optical sensing.

Spin-helical detection in a semiconductor quantum device with ferromagnetic contacts

Spin-helical states, which arise in quasi-one-dimensional (1D) channels with spin-orbital (SO) coupling, underpin efforts to realize topologically-protected quantum bits based on Majorana modes in semiconductor nanowires. Detecting helical states is challenging due to non-idealities present in real devices. Here we show by means of tight-binding calculations that by using ferromagnetic contacts it is possible to detect helical modes with high sensitivity even in the presence of realistic device effects, such as quantum interference. This is possible because of the spin-selective transmission properties of helical modes. In addition, we show that spin-polarized contacts provide a unique path to investigate the spin texture and spin-momentum locking properties of helical states. Our results are of interest not only for the ongoing development of Majorana qubits, but also as for realizing possible spin-based quantum devices, such as quantum spin modulators and interconnects based on spin-helical channels.

Vectorial Electron Spin Filtering by an All-Chiral Metal-Molecule Heterostructure.

The discovery of the electrons' chiral induced spin selective transmission (CISS) through chiral molecules has opened the pathway for manipulating spin transport in nonmagnetic structures on the nanoscale. CISS has predominantly been explored in structurally helical molecules on surfaces, where the spin selectivity affects only the spin polarization of the electrons along their direction of propagation. Here, we demonstrate a spin selective electron transmission for the point-chiral molecule 3-methylcyclohexanone (3-MCHO) adsorbed on the chiral Cu(643)R surface. Using spin- and momentum-resolved photoelectron spectroscopy, we detect a spin-dependent electron transmission through a single layer of 3-MCHO molecules that depends on all three components of the electrons' spin. Crucially, exchanging the enantiomers alters the electrons' spin component oriented parallel to the terraces of the Cu(643)R surface. The findings are attributed to the enantiomer-specific adsorption configuration on the surface. This opens the intriguing opportunity to selectively tune CISS by the enantiospecific molecule-surface interaction in all-chiral heterostructures.

A giantly chirality tunable terahertz metasurface based on 3D folded structure with vanadium dioxide

Compared with ordinary chiral materials, chiral metamaterials possess giant chiral optical response, which have been widely used in many optical applications, such as circular polarizers, chiral light imaging and asymmetric transmission. Here, a tunable 3D folded metasurface based on vanadium dioxide (VO2) is proposed to achieve giant chiral optical effect in the terahertz band. The 3D folded metasurface comprises of two folded antisymmetric rectangular split rings resonators (SRRs). By folding the SRRs at a certain angle, the mirror symmetric structure was broken. The results shows that the circular dichroism (CD) parameter reaches a maximum of 0.83 at the folding angle of 45° and the spin-selective transmission is up to 0.89. The designed 3D folded metasurface can operate in a wide incident angle range of 0–55°. What’s more, by adjusting the conductivity of VO2, the dynamic tuning of CD can be realized, achieving the switch between the “ON” and “OFF” states. The proposed 3D folded metasurfaces provides an approach to realize the giant CD, which shows potential application in many fields, such as chiral sensing, polarization control, spin optical communication, and optical imaging.

Manipulating electron-spin polarization using cysteine-DNA chiral conjugates.

The chiral molecules are potential generators of high spin-filters due to their inherent inversion asymmetric helical electric field. We report a controlled spin-selective transmission of electrons through self-assembled monolayers of 15 base-paired double-stranded deoxyribonucleic acid functionalized with two enantiomeric cysteine molecules on gold explored through the quantum mechanical tunneling effect. We observed a controlled spin polarization of 33% with dextro-cysteine, whereas a mere 8% was observed with levo-cysteine molecules using these functionalizations at room temperature. The manipulation of electron's spin merely through such a small molecule could lead to significant advancement in the spin-dependent charge transport phenomena and related applications.

Dual-band terahertz all-silicon metasurface with giant chirality for frequency-undifferentiated near-field imaging.

Chiral metasurfaces are widely used in imaging and biosensing due to their powerful light field control capabilities. Most of the work is devoted to achieving the goals of chirality enhancement and tunability, but lacks consideration of design complexity, loss, cost, and multi-band operation. In order to alleviate this situation, we propose a pair of dual-frequency giant chiral structures based on all-silicon, which can achieve excellent and opposite spin-selective transmission around 1.09 THz and 1.65 THz. The giant chirality derives from the in-plane electric and magnetic dipole moments excited in different degrees. Theoretically, the maximum circular dichroism at the two frequencies are both as high as 0.34, and the coverage bandwidths of the two giant chirality are 85.5 GHz and 41.4 GHz, respectively. The experimental results are in good agreement with the simulation results. Based on the dual-band giant chiral patterns, the terahertz near-field imaging of different Chinese character images is demonstrated at two frequencies. The frequency-undifferentiated characteristics, good intensity contrast and three-dimensional imaging information are shown by the results. This work provides new ideas for the design of terahertz devices with simple structure and multi-functions, which are expected to be applied in the field of terahertz imaging or multi-channel communication.

Observation of Giant Extrinsic Chirality Empowered by Quasi-Bound States in the Continuum

Without using intrinsic chiral metamaterials with complex structures, here we use achiral metasurfaces to realize giant extrinsic chirality empowered by quasi-bound states in the continuum (quasi-BICs). The giant extrinsic chirality in the proposed achiral metasurface is mainly attributed to the breaking of the mirror symmetry of the whole system, combining the metasurface with incident waves. The transmittance of two different polarization states and the signs of circular dichroism (CD) can be arbitrarily controlled by tilting the plane of the metasurface relative to the incoming waves. Remarkably, we simultaneously select two polarization states at different bands for a certain achiral metasurface based on the symmetry-protected dual bound states in the continuum (BICs). The measured maximum CDs approach \ifmmode\pm\else\textpm\fi{}0.85. In addition, an application of the polarization-multiplexed-field image display assisted by chiral quasi-BICs is demonstrated. This work provides a general method to control extrinsic chirality in achiral metasurfaces and offers possibilities to design high-performance multiband spin-selective transmission, biodetection, chemical analysis, and on-chip chiral manipulation.

Selective spin transmission through a driven quantum system: A new prescription

Several proposals are available to get selective spin transmission through different nano-junctions and in all the cases the regulation is done either by applying a magnetic field or by tuning spin–orbit (SO) coupling. In the present work, we explore a separate scheme where the spin-dependent transport is regulated externally by irradiating a quantum ring that bridges the contact electrodes. This is a new proposal of generating spin selective transmission through a nano-junction, to the best of our knowledge. A high degree of spin polarization along with its phase alteration can be achieved by suitably adjusting the irradiation, circumventing the regulation of magnetic field and/or SO coupling. The effect of irradiation is included through the well-known Floquet-Bloch ansatz, where all the spin-dependent transport phenomena are worked out using Green’s function formalism following the Landauer–Büttiker prescription within a tight-binding framework. Precise dependencies of light irradiation, SO coupling, magnetic flux threaded by the ring, interface sensitivity, system temperature, and impurities on spin polarization are critically investigated. Our analysis may give a new platform for spin selective electron transmission and make it applicable to other complex nano-structured materials also. We strongly believe that the present proposal can be examined in a suitable laboratory.

A dual band spin-selective transmission metasurface and its wavefront manipulation.

Chiral metasurfaces which can achieve different optical responses for left-handed and right-handed circularly polarized (CP) light have been proposed. Most of the research studies on chiral metasurfaces focus on improving circular dichroism (CD) and realizing dynamic manipulation of the chiro-optical response. However, there have only been a few reports on the multi-band chiro-optical response. Here, we propose an all-silicon chiral meta-atom which can realize spin-selective transmission in a dual band. In addition, a terahertz metasurface with spin-selective transmission through phase arrangement is designed by using chiral meta-atoms satisfying a gradient geometric phase. Under left-hand circularly polarized (LCP) incidence, the metasurface generates a focused right-hand circularly polarized (RCP) beam which is focused at a distance of 4.8 mm from the exit surface of the metasurface. Our work broadens the concept of metasurface design and may attract more researchers' attention on the applications of chiral metasurfaces.

Spin selective transmission through a multi-terminal Rashba ring with AAH modulation

For the first time we explore spin selective electron transmission through a multi-terminal nano ring subjected to Rashba spin-orbit coupling and magnetic flux, in presence of cosine modulation. The modulation is taken in the form of well known Aubry-Andre or Harper model which is associated with a phase factor that can be tuned externally with a suitable setup. Describing the quantum systems within a tight-binding framework, we compute the results based on the Green’s function formalism. Our results suggest that a large degree of spin polarization along with a phase reversal can be achieved by regulating the physical parameters associated with the system. The present analysis provides several important features that may be utilized to investigate spin dependent transport in other mutli-terminal geometries with similar kind of cosine modulation.

Spin-selective transmission through a single-stranded magnetic helix

Magnetic helix (MH) structure can be a role model for future spintronic devices. Utilizing the advantage of constructing possible magnetic configurations, in the present work first time we investigate spintronic behavior, to the best of our knowledge, in a helical geometry with finite magnetic ordering. The interplay between short-range and long-range hopping of electrons yields many non-trivial features which are thoroughly studied. Quite interestingly we see that the MH exhibits the strong chiral-induced spin selectivity effect, like what is observed in chiral molecules. Finally, to make the model more realistic we also examine the effect of helical dynamics. All the results are valid for a wide range of physical parameters, which prove the robustness of our analysis.

Giant spin-selective asymmetric transmission in multipolar-modulated metasurfaces.

Spin-selective manipulation of optical waves is widely utilized in various optical techniques and plays a key role in modern nanophotonics. While numerous efficient approaches have been applied in metasurfaces to realize spin-selective manipulation of optical waves, the implementation of giant spin-selective asymmetric transmission remains a challenge. Here, we propose an all-dielectric metasurface to realize giant tri-band spin-selective asymmetric transmission in the near infrared regime. The proposed giant spin-selective asymmetric transmission is attributed to the excitation of overlapping multipolar resonances in the dielectric elliptic cylinders, which can be well manipulated by changing the structure parameters. This research demonstrates the great potential of all-dielectric metasurfaces for spin-selective transmission manipulation, which provide helpful insights and intriguing possibilities for applications in information optics, quantum optics, optical sensing, and imaging.

Spin-Selective Transmission in Chiral Folded Metasurfaces.

Controlling the spin angular momentum of light (or circular polarization state) plays a crucial role in the modern photonic applications such as optical communication, circular dichroism spectroscopy, and quantum information processing. However, the conventional approaches to manipulate the spin of light require naturally occurring chiral or birefringent materials of bulky sizes due to the weak light-matter interactions. Here we experimentally demonstrate an approach to implement spin-selective transmission in the infrared region based on chiral folded metasurfaces that are capable of transmitting one spin state of light while largely prohibiting the other. Due to the intrinsic chirality of the folded metasurface, a remarkable circular dichroism as large as 0.7 with the maximum transmittance exceeding 92% is experimentally demonstrated. The giant circular dichroism is interpreted within the framework of charge-current multipole expansion. Moreover, the intrinsic chirality can be readily controlled by manipulating the folding angle of the metasurface with respect to the cardinal plane. Benefiting from its strong chirality and spin-dependent transmission characteristics, the proposed folded metasurface may be applied to a range of novel photon-spin selective devices for optical communication technologies and biophotonics.

Spin-Selective Transmission and Devisable Chirality in Two-Layer Metasurfaces

Chirality is a nearly ubiquitous natural phenomenon. Its minute presence in most naturally occurring materials makes it incredibly difficult to detect. Recent advances in metasurfaces indicate that they exhibit devisable chirality in novel forms; this finding offers an effective opening for studying chirality and its features in such nanostructures. These metasurfaces display vast possibilities for highly sensitive chirality discrimination in biological and chemical systems. Here, we show that two-layer metasurfaces based on twisted nanorods can generate giant spin-selective transmission and support engineered chirality in the near-infrared region. Two designed metasurfaces with opposite spin-selective transmission are proposed for treatment as enantiomers and can be used widely for spin selection and enhanced chiral sensing. Specifically, we demonstrate that the chirality in these proposed metasurfaces can be adjusted effectively by simply changing the orientation angle between the twisted nanorods. Our results offer simple and straightforward rules for chirality engineering in metasurfaces and suggest intriguing possibilities for the applications of such metasurfaces in spin optics and chiral sensing.

Pancharatnam-Berry Phase Induced Spin-Selective Transmission in Herringbone Dielectric Metamaterials.

A dielectric metamaterial approach for achieving spin-selective transmission of electromagnetic waves is proposed. The design is based on spin-controlled constructive or destructive interference between propagating phase and Pancharatnam-Berry phase. The dielectric metamaterial, consisting of monolithic silicon herringbone structures, exhibits a broadband operation in the terahertz regime.