Jinghua Teng

Geometric phases are fundamental to wave physics and underpin a broad range of optical phenomena. The most prominent example, the Pancharatnam–Berry (PB) phase, originates from polarization evolution during wave propagation. In contrast, geometric phases associated with optical resonances and cavities remain largely unexplored. Here, we uncover the relation between the generalized PB phase and the far-field polarization evolution in bound states in the continuum (BIC) cavities. We demonstrate the continuous homotopic evolution of vortex lasing modes through geometric-phase engineering of BIC resonances. To experimentally validate this concept, we realize metasurface lasers composed of titanium dioxide hole arrays integrated with CdSe/CdxZn1–xS core/shell colloidal quantum wells as the gain medium. Our results reveal a previously unexplored form of spin–orbit interaction in BIC cavities under oblique incidence and provide a versatile route for on-chip control of polarization and orbital angular momentum in nanolasers.

The concept of singular phases at the point of darkness has been extensively studied using various optical systems, such as metamaterials and thin-film cavities, mainly for refractive index sensing. However, these systems typically work at an oblique angle of incidence. Achieving a singular phase at normal incidence is vital for practical sensing and flat-optics applications, but it remains challenging. Here, we demonstrate the singular phase at normal incidence using a grating-coupled thin-film cavity that functions at optical wavelengths. By optimizing the structural parameters of the grating and thin-film cavity, we achieve zero reflection with an abrupt phase shift at the polarization-dependent resonance of the grating. In addition, we introduce a spectrally tunable singular phase at normal incidence by integrating a phase change material (PCM) into the cavity. Using a lossless PCM, such as Sb2S3, we achieve a phase singularity with continuous spectral tunability up to 203 nm by altering its phase from amorphous to crystalline, a key feature for phase engineering in flat optics.

After decades of research, symmetry breaking in high-temperature cuprate superconductors remains a key issue to resolve and is relevant to understanding their exotic quantum phases. In the prototypical cuprate superconductor, Bi₂Sr₂CaCu₂O_8+δ (Bi2212), the possible symmetry breaking has been mostly examined microscopically with scanning tunneling microscopy and photoemission spectroscopy. However, macroscopic evidence and the direct implications for electronic transport have remained elusive. Using superconductivity-enhanced nonreciprocal transport, we report macroscopic evidence of inversion symmetry breaking in Bi2212. While the inversion symmetry breaking is subtle, its effect on nonreciprocal transport is significantly enhanced by the vortex motion during the superconducting transition, leading to a robust manifestation of inversion symmetry breaking in macroscopic transport. Combining angle-resolved nonreciprocal transport and 3D tight-binding model calculations, we derive that the inversion symmetry breaking is due to subtle crystal distortions that give rise to both in-plane and out-of-plane polar axes. Our work not only establishes nonreciprocal transport as a sensitive macroscopic probe to provide electrical transport-based evidence of fine symmetry breaking in Bi2212, but also paves the way for novel device applications such as high-temperature superconducting diodes and superconducting spintronics.

UV light triggers halide-to-viologen PIET in crystals, forming long-lived radicals that reversibly enhance tunable solid-state emission; heating reverses the photoinduced state.

Barium strontium titanate (BST) thin films are distinguished for their ferroelectric behavior which makes them highly promising for optical and microwave applications, but there is a lack of studies in the important terahertz (THz) frequency range. In this work, we report the deposition of high‐quality BST films by physical vapor deposition at high temperatures and its application in tunable THz metadevices. The Ba _0.6 Sr _0.4 TiO ₃ film exhibits a full width at half maximum of 0.57° in high‐resolution X‐ray diffraction (HR‐XRD) spectroscopy, a real dielectric constant of 140 at 0.2 THz. By integrating interdigitated electrodes (IDEs) of varying periodicities, we systematically investigated their impact and identified a 100 µm electrode separation as the optimal electrode separation for maximizing THz response modulation. A metasurface using Ba _0.6 Sr _0.4 TiO ₃ thin film as the active material working in reflection mode has been designed using finite‐difference time‐domain (FDTD) simulation, and the fabricated metadevice experimentally demonstrated a remarkable resonance shifts of up to 5.5 GHz under applied voltage. These findings underscore the potential of BST for reconfigurable intelligent metasurfaces and future electrically tunable THz device applications.

A tunable thin film coating based on a phase change material was developed for adjustable directional control of thermal emission across a broad long-wave infrared spectral bandwidth.

Extreme light confinement down to the atomic scale has been theoretically predicted for ultrathin, Ta-based transition metal dichalcogenides (TMDs). In this work, we report the observation of highly confined plasmons in 2H-TaS₂ monolayers and bilayers via momentum-resolved electron energy loss spectroscopy (q-EELS), with a resolution of 0.0056 Å⁻¹. Momentum-dispersed two-dimensional (2D) plasmon resonances were found to exhibit a lateral confinement ratio up to 300 at large wave vectors of q = 0.15 Å⁻¹ and slow light behaviour with a group velocity ~10^-4c. Moreover, we observed a transition from 2D to 3D Coulomb interaction in the high-momentum regime, equivalent to light confinement volumes of 1-2 nm³. Remarkably, the resonant modes do not enter the electron-hole continuum, potentially enabling even further enhanced optical field confinements for this material at cryogenic temperatures.

Enhanced photoluminescence (PL) in transition metal dichalcogenides (TMDs) is critical for their application in optoelectronics. In this study, we report a 99 × PL enhancement in a superacid bis(trifluoromethane) sulfonimide (TFSI)-treated MoS_2(1-x)Se_2x alloy. The alloy's optical bandgap is tunable by changing its stoichiometry, allowing for PL enhancement at tailored positions. The PL enhancement is robust even at high excitation power, overcoming the limitation of exciton-exciton annihilation observed in MoS₂. Through molecular dynamics simulations and spectroscopic analysis, we demonstrate that the MoS_2(1-x)Se_2x monolayer inherently exhibits moderate strain, which shifts the van Hove singularity in the S-rich domain. Furthermore, density functional theory calculations reveal the absence of a pronounced van Hove feature in the alloy configuration. Our findings extend the range of materials amenable to superacid treatment and open new avenues for optoelectronic applications, particularly those requiring high excitation powers.