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1. Charge Density Waves and Magnetism in Topological Semimetal Candidates GdSb x Te 2− x − δ

   https://doi.org/10.1002/qute.201900045  

   Lei, Shiming ; Duppel, Viola ; Lippmann, Judith M. ; Nuss, Jürgen ; Lotsch, Bettina V. ; Schoop, Leslie M. ( July 2019 , Advanced Quantum Technologies)

   Many topological semimetals are known to exhibit exceptional electronic properties, which are the fundamental basis for design of novel devices and further applications. Materials containing the structural motif of a square net are known to frequently be topological semimetals. In this work, the synthesis and structural characterization of the square‐net‐based magnetic topological semimetal candidates GdSb_xTe_2−x−δ(0,δindicating the vacancy level) are reported. The structural evolution of the series with Sb substitution is studied, finding a transition between a simple tetragonal square‐net structure to complex superstructure formations due to the presence of charge density waves. The structural modulations coincide with a significant modification of the magnetic order. This work thus establishes GdSb_xTe_2−x−δas a platform to study the interplay between crystal symmetry, band filling, charge density wave, and magnetism in a topological semimetal candidate.

    

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2. Compositional Control and Optimization of Molecular Beam Epitaxial Growth of (Sb 2 Te 3 ) 1–x (MnSb 2 Te 4 ) x Magnetic Topological Insulators

   https://doi.org/10.1021/acs.cgd.1c01453  

   Levy, Ido ; Forrester, Candice ; Deng, Haiming ; Roldan-Gutierrez, Manuel ; McCartney, Martha R. ; Smith, David J. ; Testelin, Christophe ; Krusin-Elbaum, Lia ; Tamargo, Maria C. ( May 2022 , Crystal Growth & Design)
3. Emerging role of local and extended range molecular structures on functionalities of topological phases of (Na 2 O) x (P 2 O 5 ) 100‐ x glasses using Raman scattering and modulated DSC

   https://doi.org/10.1111/ijag.15809  

   Mandal, Avik ; Gogi, Vamshi Kiran ; Mohanty, Chandi ; Chbeir, Ralph ; Boolchand, Punit ( July 2020 , International Journal of Applied Glass Science)

   Raman scattering is a powerful probe oflocal structure (LS)of glasses. In Sodium Phosphate Glasses (SPGs), we show that bothLScomposed of Qⁿspecies andExtended Range Structures (ERS)composed of Long Chains (LCs), Large Rings (LRs), and Small Rings (SRs) can be decoded by Raman scattering. The trimodal distribution of P‐O_terminalstretch modes of Q²species and P‐O_bridgingatx < 50% are manifestations of theseERS. These two pairs of triads of modes are uniquely identified with Q²units present in either LCs, or LRs, or SRs. The existence three phases of c‐NaPO₃composed of 3‐membered rings, 6‐membered rings, and infinitely long chains has facilitated the identification. The Intermediate Phase (IP) in SPGs extends in the 37.5 < x < 46.0% range, the Stressed‐rigid Phase in the 46.0% < x < 50%, and the Flexible Phase in the 18% < x < 37.5% range of soda. We show the IP consists predominantly of LCs (82%), with a minority of LRs (15%) and SRs (3%). The LR‐ and SR‐fractions increase measurably in the non‐IP phases. The structural finding is in harmony with the high configurational entropy of the IP glasses that leads aging to be qualitatively suppressed.

    

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4. Strain‐Driven Mixed‐Phase Domain Architectures and Topological Transitions in Pb 1− x Sr x TiO 3 Thin Films

   https://doi.org/10.1002/adma.202203469  

   Kavle, Pravin ; Zorn, Jacob A. ; Dasgupta, Arvind ; Wang, Bo ; Ramesh, Maya ; Chen, Long‐Qing ; Martin, Lane W. ( August 2022 , Advanced Materials)

   The potential for creating hierarchical domain structures, or mixtures of energetically degenerate phases with distinct patterns that can be modified continually, in ferroelectric thin films offers a pathway to control their mesoscale structure beyond lattice‐mismatch strain with a substrate. Here, it is demonstrated that varying the strontium content provides deterministic strain‐driven control of hierarchical domain structures in Pb_1−xSr_xTiO₃ solid‐solution thin films wherein two types,c/aanda₁/a₂, of nanodomains can coexist. Combining phase‐field simulations, epitaxial thin‐film growth, detailed structural, domain, and physical‐property characterization, it is observed that the system undergoes a gradual transformation (with increasing strontium content) from droplet‐likea₁/a₂ domains in ac/adomain matrix, to a connected‐labyrinth geometry ofc/adomains, to a disconnected labyrinth structure of the same, and, finally, to droplet‐likec/adomains in ana₁/a₂ domain matrix. A relationship between the different mixed‐phase modulation patterns and its topological nature is established. Annealing the connected‐labyrinth structure leads to domain coarsening forming distinctive regions of parallelc/aanda₁/a₂ domain stripes, offering additional design flexibility. Finally, it is found that the connected‐labyrinth domain patterns exhibit the highest dielectric permittivity.

    

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5. Emerging Weyl Semimetal States in Ternary TaP x As 1− x Alloys: Insights from Electronic and Topological Analysis

   https://doi.org/10.1002/qute.202300072  

   Nourizadeh, Samira Sadat ; Vaez, Aminollah ; Vashaee, Daryoosh ( May 2023 , Advanced Quantum Technologies)

   This study presents a thorough analysis of the electronic structures of the TaP_xAs_1−xseries of compounds, which are of significant interest due to their potential as topological materials. Using a combination of first principles and Wannier‐based tight‐binding methods, this study investigates both the bulk and surface electronic structures of the compounds for varying compositions (x = 0, 0.25, 0.50, 0.75, 1), with a focus on their topological properties. By using chirality analysis, (111) surface electronic structure analysis, and surface Fermi arcs analysis, it is established that the TaP_xAs_1−xcompounds exhibit topologically nontrivial behavior, characterized as Weyl semimetals (WSMs). The effect of spin–orbit coupling (SOC) on the topological properties of the compounds is further studied. In the absence of SOC, the compounds exhibit linearly dispersive fourfold degenerate points in the first Brillouin zone (FBZ) resembling Dirac semimetals. However, the introduction of SOC induces a phase transition to WSM states, with the number and position of Weyl points (WPs) varying depending on the composition of the alloy. For example, TaP has 12 WPs in the FBZ. The findings provide novel insights into the electronic properties of TaP_xAs_1−xcompounds and their potential implications for the development of topological materials for various technological applications.

    

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