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Recently twisted bilayer graphene (t-BLG) has emerged as a strongly correlated physical platform. Besides the apparent significance of band flatness, band topology may be another critical element in t-BLG and yet receives much less attention. Here we report the compelling evidence for nontrivial noninteracting Moiré band topology in t-BLG through a systematic nonlocal transport study and a -theory examination. The nontrivial topology manifests itself as two pronounced nonlocal responses in the electron and hole superlattice gaps. We show that the nonlocal responses are robust to the twist angle and edge termination, exhibiting a universal scaling law. We elucidate that, although Berry curvature is symmetry-trivialized, two nontrivial invariants characterize the Moiré Dirac bands, validating the topological origin of the observed nonlocal responses. Our findings not only provide a new perspective for understanding the strongly correlated t-BLG but also suggest a potential strategy to achieve topological metamaterials from trivial vdW materials.
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http://dx.doi.org/10.1021/acs.nanolett.0c02131 | DOI Listing |
High-efficiency fiber-to-chip couplers are essential for high-performance optical interconnects. In this Letter, we experimentally demonstrate two inverse-designed silicon-on-insulator (SOI) couplers tailored for single-mode fibers (SMFs) in the C and O telecommunication bands. The O-band coupler represents the first, to the best of our knowledge, experimental demonstration of a topology-optimized coupler for this band while maintaining a minimum feature size of 120 nm.
View Article and Find Full Text PDFFront Chem
February 2025
School of Mathematics, Jilin University, Changchun, China.
The investigation of two-dimensional materials exhibiting half-metallicity and topological features has become a rapidly growing area of interest, driven by their immense potential in nanoscale spintronics and quantum electronics. In this work, we present a comprehensive study of a two-dimensional PrClS monolayer, revealing its remarkable electronic and mechanical properties. Under its ferromagnetic ground state, the PrClS monolayer is shown to exhibit half-metallic behavior with 100% spin polarization originating from the spin-up channel.
View Article and Find Full Text PDFNature
March 2025
Department of Physics and Guangdong Basic Research Center of Excellence for Quantum Science, Southern University of Science and Technology, Shenzhen, China.
Magnonic systems provide a fertile playground for bosonic topology, for example, Dirac and Weyl magnons, leading to a variety of exotic phenomena such as charge-free topologically protected boundary modes, the magnon thermal Hall effect and the magnon spin Nernst effect. However, their understanding has been hindered by the absence of fundamental symmetry descriptions of magnetic geometries and spin Hamiltonians primarily governed by isotropic Heisenberg interactions. The ensuing magnon dispersions enable gapless magnon band nodes that go beyond the scenario of representation theory of the magnetic space groups, thus referred to as unconventional magnons.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
March 2025
State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan, 250100, China.
The contradictory relationship between band gaps and the second-harmonic generation (SHG) response constitutes a formidable challenge in the rational design of infrared nonlinear optical (IR NLO) crystals. In oxide-based crystals, the incorporation of strongly distorted octahedra containing d° cations as central elements are a common approach to enhance SHG responses, while inadvertently leading to a significant decrease in band gaps due to the unfavorable energy level splitting. In this study, an innovative "4d/5s electron band-inversion" strategy is introduced to enhance SHG response while preserving a wide band gap within the octahedron-symmetry-protected langasite structure.
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March 2025
Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA.
Inducing superconducting correlations in chiral edge states is predicted to generate topologically protected zero energy modes with exotic quantum statistics. Experimental efforts so far have focused on engineering interfaces between superconducting materials-typically amorphous metals-and semiconducting quantum Hall or quantum anomalous Hall systems. However, the strong interfacial disorder inherent in this approach can prevent the formation of isolated topological modes.
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