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1. Molecular Design for Optically Induced Magnetization: Targeting Excited State Orbital Degeneracy in Tungsten(V) Complexes

   https://doi.org/10.1021/jacs.5c03783  

   Ramsier, Ian E; Mandato, Alysia; Saxena, Sunil; Transue, Wesley J (June 2025, Journal of the American Chemical Society)

   The rise of quantum information science has spurred chemists to prepare new molecules that serve as useful building blocks in quantum technologies of the future. Implementation of molecular spin-based qubits requires new methods to induce high spin polarization of samples. Herein, we report design criteria to develop axially symmetric spin-1/2 molecules amenable to optically induced magnetization (OIM), a technique using circularly polarized (CP) excitation to deliver spin polarization. We apply these criteria to develop a series of tungsten(V) chalcogenide complexes that are demonstrated to have large spin-sensitive responses to CP light using magnetic circular dichroism (MCD) that could allow up to ∼20% spin polarization through OIM. Pulsed electron paramagnetic resonance (EPR) spectra reveal these systems have improved relaxation times over molecules like K2IrCl6, a species recently investigated by OIM, and field-swept electron spin−echo (FS-ESE) experiments show they have a remarkable lack of anisotropy in their phase-memory Tm times. The design criteria are general and point toward future ways to improve OIMinitializable qubits. 

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2. 3D Janus plasmonic helical nanoapertures for polarization-encrypted data storage

   https://doi.org/10.1038/s41377-019-0156-8  

   Chen, Yang; Yang, Xiaodong; Gao, Jie (May 2019, Light: Science & Applications)

   Abstract Helical structures have attracted considerable attention due to their inherent optical chirality. Here, we report a unique type of 3D Janus plasmonic helical nanoaperture with direction-controlled polarization sensitivity, which is simply fabricated via the one-step grayscale focused ion beam milling method. Circular dichroism in transmission of as large as 0.72 is experimentally realized in the forward direction due to the spin-dependent mode coupling process inside the helical nanoaperture. However, in the backward direction, the nanoaperture acquires giant linear dichroism in transmission of up to 0.87. By encoding the Janus metasurface with the two nanoaperture enantiomers having specified rotation angles, direction-controlled polarization-encrypted data storage is demonstrated for the first time, where a binary quick-response code image is displayed in the forward direction under the circularly polarized incidence of a specified handedness, while a distinct grayscale image is revealed in the backward direction under linearly polarized illumination with a specified azimuthal angle. We envision that the proposed Janus helical nanoapertures will provide an appealing platform for a variety of applications, which will range from multifunctional polarization control, enantiomer sensing, data encryption and decryption to optical information processing. 

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3. Large exchange-driven intrinsic circular dichroism of a chiral 2D hybrid perovskite

   https://doi.org/10.1038/s41467-024-46851-2  

   Li, Shunran; Xu, Xian; Kocoj, Conrad A.; Zhou, Chenyu; Li, Yanyan; Chen, Du; Bennett, Joseph A.; Liu, Sunhao; Quan, Lina; Sarker, Suchismita; et al (March 2024, Nature Communications)

   Abstract In two-dimensional chiral metal-halide perovskites, chiral organic spacers endow structural and optical chirality to the metal-halide sublattice, enabling exquisite control of light, charge, and electron spin. The chiroptical properties of metal-halide perovskites have been measured by transmissive circular dichroism spectroscopy, which necessitates thin-film samples. Here, by developing a reflection-based approach, we characterize the intrinsic, circular polarization-dependent complex refractive index for a prototypical two-dimensional chiral lead-bromide perovskite and report large circular dichroism for single crystals. Comparison with ab initio theory reveals the large circular dichroism arises from the inorganic sublattice rather than the chiral ligand and is an excitonic phenomenon driven by electron-hole exchange interactions, which breaks the degeneracy of transitions between Rashba-Dresselhaus-split bands, resulting in a Cotton effect. Our study suggests that previous data for spin-coated films largely underestimate the optical chirality and provides quantitative insights into the intrinsic optical properties of chiral perovskites for chiroptical and spintronic applications. 

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4. Optical Chirality Detection Using a Topological Insulator Transistor

   https://doi.org/10.1002/adom.202002210  

   Huang, Shouyuan; Xu, Xianfan (March 2021, Advanced Optical Materials)

   Abstract Optical chirality is an effective means in screening molecules and their enantiomers in bioengineering, and recently has garnered attention as an implementation of qubits in quantum information processing. The conventional detection of circularly polarized light (CPL) is based on phase retardation and polarization separation using multiple optical components. An intrinsic solid‐state chirality detection device would be favorable for easier integration and implementation. Optical spin injection to the spin‐momentum‐locked topological surface states of topological insulators (TIs) by circularly polarized light leads to a directional DC photocurrent and hence possible circular polarization detection. However, this DC photocurrent is also accompanied by other photo‐responses. Here, a photodetection strategy using a TI transistor which senses CPL without the use of any additional components is demonstrated, it achieves a uniform response over the entire device with a sensitivity ≈5.6%. The Stokes parameters can also be extracted by arithmetic operation of photocurrents obtained with different bias and gate for a complete characterization of a polarized light beam. Therefore, this method enables chirality detection and Stokes parameter analysis using a single device. The proposed miniaturized intrinsic chirality detectors facilitate polarimetry sensing in applications from circular dichroism spectroscopy to biomedical diagnosis. 

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5. Highly Efficient Anisotropic Chiral Plasmonic Metamaterials for Polarization Conversion and Detection

   Bai, Jing; Yao, Yu (August 2021, ACS nano)

   null (Ed.)

   Plasmonic chiral metamaterials have attracted broad research interest because of their potential applications in optical communication, biomedical diagnosis, polarization imaging, and circular dichroism spectroscopy. However, optical losses in plasmonic structures severely limit practical applications. Here, we present the design concept and experimental demonstration for highly efficient subwavelength-thick plasmonic chiral metamaterials with strong chirality. The proposed designs utilize plasmonic metasurfaces to control the phase and polarization of light and exploit anisotropic thin-film interference effects to enhance optical chirality while minimizing optical loss. Based on such design concepts, we demonstrated experimentally optical devices such as circular polarization filters with transmission efficiency up to 90% and extinction ratio >180, polarization converters with conversion efficiency up to 90%, as well as on-chip integrated microfilter arrays for full Stokes polarization detection with high accuracy over a broad wavelength range (3.5–5 μm). The proposed design concepts are applicable from near-infrared to Terahertz regions via structural engineering. 

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