More Like this

1. Spin structure and dynamics of the topological semimetal Co3Sn2-xInxS2

   https://doi.org/10.1038/s41535-022-00523-w  

   Neubauer, Kelly J. ; Ye, Feng ; Shi, Yue ; Malinowski, Paul ; Gao, Bin ; Taddei, Keith M. ; Bourges, Philippe ; Ivanov, Alexandre ; Chu, Jiun-Haw ; Dai, Pengcheng ( December 2022 , npj Quantum Materials)

   The anomalous Hall effect (AHE), typically observed in ferromagnetic (FM) metals with broken time-reversal symmetry, depends on electronic and magnetic properties. In Co₃Sn_2-xIn_xS₂, a giant AHE has been attributed to Berry curvature associated with the FM Weyl semimetal phase, yet recent studies report complicated magnetism. We use neutron scattering to determine the spin dynamics and structures as a function ofxand provide a microscopic understanding of the AHE and magnetism interplay. Spin gap and stiffness indicate a contribution from Weyl fermions consistent with the AHE. The magnetic structure evolves fromc-axis ferromagnetism at$$x = 0$$$x=0$to a canted antiferromagnetic (AFM) structure with reducedc-axis moment and in-plane AFM order at$$x = 0.12$$$x=0.12$and further reducedc-axis FM moment at$$x = 0.3$$$x=0.3$. Since noncollinear spins can induce non-zero Berry curvature in real space acting as a fictitious magnetic field, our results revealed another AHE contribution, establishing the impact of magnetism on transport.

    

   more » « less
2. Exchange biased anomalous Hall effect driven by frustration in a magnetic kagome lattice

   https://doi.org/10.1038/s41467-020-14326-9  

   Lachman, Ella ; Murphy, Ryan A. ; Maksimovic, Nikola ; Kealhofer, Robert ; Haley, Shannon ; McDonald, Ross D. ; Long, Jeffrey R. ; Analytis, James G. ( January 2020 , Nature Communications)

   Co$$_{3}$$${}_3$Sn$$_{2}$$${}_2$S$$_{2}$$${}_2$is a ferromagnetic Weyl semimetal that has been the subject of intense scientific interest due to its large anomalous Hall effect. We show that the coupling of this material’s topological properties to its magnetic texture leads to a strongly exchange biased anomalous Hall effect. We argue that this is likely caused by the coexistence of ferromagnetism and geometric frustration intrinsic to the kagome network of magnetic ions, giving rise to spin-glass behavior and an exchange bias.

    

   more » « less
3. Giant field-like torque by the out-of-plane magnetic spin Hall effect in a topological antiferromagnet

   https://doi.org/10.1038/s41467-021-26453-y  

   Kondou, Kouta ; Chen, Hua ; Tomita, Takahiro ; Ikhlas, Muhammad ; Higo, Tomoya ; MacDonald, Allan H. ; Nakatsuji, Satoru ; Otani, YoshiChika ( November 2021 , Nature Communications)

   Spin-orbit torques (SOT) enable efficient electrical control of the magnetic state of ferromagnets, ferrimagnets and antiferromagnets. However, the conventional SOT has severe limitation that only in-plane spins accumulate near the surface, whether interpreted as a spin Hall effect (SHE) or as an Edelstein effect. Such a SOT is not suitable for controlling perpendicular magnetization, which would be more beneficial for realizing low-power-consumption memory devices. Here we report the observation of a giant magnetic-field-like SOT in a topological antiferromagnet Mn₃Sn, whose direction and size can be tuned by changing the order parameter direction of the antiferromagnet. To understand the magnetic SHE (MSHE)- and the conventional SHE-induced SOTs on an equal footing, we formulate them as interface spin-electric-field responses and analyzed using a macroscopic symmetry analysis and a complementary microscopic quantum kinetic theory. In this framework, the large out-of-plane spin accumulation due to the MSHE has an inter-band origin and is likely to be caused by the large momentum-dependent spin splitting in Mn₃Sn. Our work demonstrates the unique potential of antiferromagnetic Weyl semimetals in overcoming the limitations of conventional SOTs and in realizing low-power spintronics devices with new functionalities.

    

   more » « less
4. Anomalous Landau quantization in intrinsic magnetic topological insulators

   https://doi.org/10.1038/s41467-023-40383-x  

   Chong, Su Kong ; Lei, Chao ; Lee, Seng Huat ; Jaroszynski, Jan ; Mao, Zhiqiang ; MacDonald, Allan H. ; Wang, Kang L. ( August 2023 , Nature Communications)

   The intrinsic magnetic topological insulator, Mn(Bi_1−xSb_x)₂Te₄, has been identified as a Weyl semimetal with a single pair of Weyl nodes in its spin-aligned strong-field configuration. A direct consequence of the Weyl state is the layer dependent Chern number,$$C$$$C$. Previous reports in MnBi₂Te₄thin films have shown higher$$C$$$C$states either by increasing the film thickness or controlling the chemical potential. A clear picture of the higher Chern states is still lacking as data interpretation is further complicated by the emergence of surface-band Landau levels under magnetic fields. Here, we report a tunable layer-dependent$$C$$$C$ = 1 state with Sb substitution by performing a detailed analysis of the quantization states in Mn(Bi_1−xSb_x)₂Te₄dual-gated devices—consistent with calculations of the bulk Weyl point separation in the doped thin films. The observed Hall quantization plateaus for our thicker Mn(Bi_1−xSb_x)₂Te₄films under strong magnetic fields can be interpreted by a theory of surface and bulk spin-polarised Landau level spectra in thin film magnetic topological insulators.

    

   more » « less
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.

    

   more » « less