Tian Shang

The rapid development of nanoscale integrated photonics demands core materials combining high transparency, high refractive index, and low optical loss. In this work, semi-transparent polycrystalline copper iodide (CuI) bulks were fabricated via the vertical Bridgman technique. Structural characterization reveals dense, large-grained microstructures. To reliably evaluate the material’s intrinsic optical parameters, spectroscopic ellipsometry was performed on a nanometer-thick companion CuI thin film, yielding a high refractive index (∼2.2) that ensures strong optical confinement when paired with common low-index claddings and strong subwavelength optical confinement. Critically, to assess the intrinsic optical transport properties before integrating into nanoscale optical waveguides, and exclude the influence of micro−nano fabrication complexities, a polycrystalline bulk waveguide configuration was utilized. Remarkably, despite the presence of grain boundaries, the material exhibits an attenuation as low as 20 dB/cm in the 900−1100 nm spectral range. This performance, achieved in a non-optimized polycrystalline state, decisively demonstrates the excellent intrinsic waveguiding potential of CuI. These findings establish CuI as a highly promising candidate for next-generation high-index-contrast photonic devices and provide a solid foundation for future CuI-based integrated optics.

It has been suggested that the anisotropic behavior of orbital transport can be distinct from that of the spin counterpart. On another front, the microscopic mechanisms underlying the anomalous Hall effect and the spin Hall effect are generally categorized into the intrinsic Berry curvature mechanism and the extrinsic mechanism induced by disorder scattering, each with distinct scaling relations. A similar analysis for orbital transport has rarely been performed. Here, we investigate both aspects of the orbital current generation in a light metal V. The orbital-to-spin conversion is achieved using a heavy metal Pt insertion layer or Ni as the ferromagnetic layer. Benefiting from the epitaxial growth of V with a low disorder strength, the orbital current generation is characterized by a large transverse conductivity and long diffusion length, consistent with the expectation for an intrinsic orbital Hall effect. Across all the heterostructures studied, we confirm the orbital current's isotropic nature, i.e., the orbital current generation is barely affected when the charge current is applied along different crystallographic directions, consistent with the high-symmetry crystal structure. Crucially, the intrinsic nature of the orbital current generation is demonstrated by the scaling analysis, showing a scattering-independent orbital Hall conductivity.

Altermagnetism has attracted considerable research interest as a new platform for spintronic functionalities without net magnetization. Extending altermagnetism to two dimensions is highly desirable for applications but remains challenging because the symmetries of most two-dimensional (2D) collinear magnetic materials preserve spin degeneracy, rendering experimentally verified intrinsic two-dimensional altermagnets elusive in bulk materials. Recent theoretical advances demonstrate a route to two-dimensional altermagnetism through surface-induced symmetry breaking in layered antiferromagnetic materials. Using angle-resolved photoemission spectroscopy and first-principles calculations, we directly resolve such intrinsic 2D altermagnetic electronic states on the surface of YbMn ₂ Ge ₂ that emerge despite the magnetically compensated bulk order. These surface states are guaranteed by the quantized Berry phase of the bulk states which enforces their emergence at the terminating surface. Beyond the realization of pure 2D altermagnetism, we further identify a symmetry-protected p-wave orbital angular momentum texture localized at the surface, revealing an orbital analogue of unconventional p-wave magnetic order. Moreover, the anomalous Hall effect is observed, which is unexpected in pristine YbMn ₂ Ge ₂ with combined time reversal and inversion symmetry. Our work experimentally establishes antiferromagnetic surfaces as a realizable versatile platform for realizing two-dimensional altermagnetism and uncovers a route toward spin–orbital quantum phenomena in magnetic materials.

Recently, preliminary magnetic field-reentrant superconductivity manifested in high-temperature (Tc) Eu-doped infinite-layer (IL) nickelates, beyond analogous discoveries exclusively in low-Tc systems. This evokes intriguing fundamental issues about potential quantum-phase boundary and criticality between unconventional superconductivity and field-reentrant-one, which are inexplicable owing to formidable challenges in growing IL-nickelates towards later-series rare-earths. Herein, we open up chemical avenues to enable effective growth of (RE1-yRE'y)1-xEuxNiO2 (RE/RE': Pr, Nd, Sm, Gd, Dy), giving rise to discoveries of RE-4f-related quantum rivalries between high-Tc and reentrant superconductivity. Robust magnetic-field-reentrant superconductivity with uniaxial anisotropy is observed at superconducting-dome boundaries, stemming from Eu2+-4f7 associated competitions between magnetic-fluctuation promoted pairing and exchange-field interactions. Their quantum-criticality is further modulable via RE(RE’)-magnetism, which either reinforces reentrancy or elevates Tc (~40.1 K) with more robust critical-current-density (~266 kA/cm2 at 2 K) beyond Sr-/Ca-doped counterparts. Our synthetic route enables the establishment of an ideal platform via IL-nickelates for studying 4f-related unconventional superconductivity and quantum-criticality.

Excitons in semiconductors with negligible group velocity have been extensively investigated using optical methodologies. However, one significant characteristic of excitons for information transmission applications is their mobility, which poses a challenge in band-gapped systems. Meanwhile, three-dimensional dispersive excitons formed with electrons in a partially occupied conduction band are rare due to electron screening effect, excitonic instability, and the technical challenge of realizing them. Here, using angle-resolved photoemission spectroscopy and theoretical simulation, we observed dispersive excitonic bound states that are manifested as replica valence bands across a large portion of the three-dimensional Brillouin in the metallic material TbNiC2. Furthermore, our research indicates that the excitonic bound states are promoted by low density of states of free charges induced by electron-phonon coupling, and the resonance between topological surface and bulk states. Our findings provide a new thread to generate and stabilize three dimensional dispersive excitons in metals, which paves the way for the exploration of novel materials potentially suitable as metallic optoelectronic media which could conduct both electronic and excitonic signals simultaneously.

Current‐induced spin‐orbit torque (SOT) plays a crucial role in the next‐generation spin‐orbitronics. Enhancing its efficiency is both fundamentally and practically interesting and remains a challenge to date. Recently, orbital counterparts of spin effects that do not rely on the spin‐orbit coupling (SOC) have been found as an alternative mechanism to realize it. This work highlights the engineering of copper oxidation states for manipulating the orbital current and its torque in the ‐based heterostructures. The orbital hybridization and thus the orbital‐Rashba‐Edelstein effect at the /Cu interfaces are significantly enhanced by increasing the copper oxidation state, yielding a torque efficiency that is almost ten times larger than the conventional heavy metals. The /Cu interface, rather than the widely accepted CuO/Cu interface, is revealed to account for the enhanced SOT performance in the ‐based heterostructures. In addition, the torque efficiency can be alternatively switched between high and low thresholds through the redox reaction. The current results establish an exotic and robust strategy for engineering the orbital current and SOT for spin‐orbitronics, which applies to other weak‐SOC materials.

Current-induced spin-orbit torque (SOT) plays a crucial role in the next-generation spin-orbitronics. Enhancing its efficiency is both fundamentally and practically interesting and remains a challenge to date. Recently, orbital counterparts of spin effects that do not rely on the spin-orbit coupling (SOC) have been found as an alternative mechanism to realize it. This work highlights the engineering of copper oxidation states for manipulating the orbital current and its torque in the CuO$_x$-based heterostructures. The orbital hybridization and thus the orbital-Rashba-Edelstein effect at the CuO$_x$/Cu interfaces are significantly enhanced by increasing the copper oxidation state, yielding a torque efficiency that is almost ten times larger than the conventional heavy metals. The Cu$_4$O$_3$/Cu interface, rather than the widely accepted CuO/Cu interface, is revealed to account for the enhanced SOT performance in the CuO$_x$-based heterostructures. In addition, the torque efficiency can be alternatively switched between high and low thresholds through the redox reaction. The current results establish an exotic and robust strategy for engineering the orbital current and SOT for spin-orbitronics, which applies to other weak-SOC materials.