Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q72: Antiferromagnetic Topological MaterialsFocus Recordings Available
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Sponsoring Units: DMP GMAG DCMP Chair: Madhab Neupane, University of Central Florida; Yuhang Li, University of California, Riverside Room: Hyatt Regency Hotel -Jackson Park D |
Wednesday, March 16, 2022 3:00PM - 3:36PM |
Q72.00001: Quantum point junction on the surface of an antiferromagnetic topological insulator Invited Speaker: Nicodemos Varnava Engineering and manipulation of unidirectional channels has been achieved in quantum Hall systems, leading to the construction of electron interferometers and giving rise to the field of electron quantum optics. However, these material systems require strong external magnetic fields and ultra low temperatures to be realized, which limits their applicability in microelectronic applications. In addition, mixing and interference of edge-state wave functions is achieved by bringing two channels in close proximity to enable tunneling. These so-called quantum point contacts are highly sensitive to their local environment and are hard to tune. In this work, we find that antiferromagnetic topological insulators offer a novel opportunity to realize robust and controllable quantum point junctions due to existence of two distinct types of gapless unidirectional channels, one from antiferromagnetic domain walls and the other from single-height steps. Their distinct geometric nature allows them to intersect robustly to form quantum point junctions, which then enables their control by magnetic and electrostatic local probes. Encouraged by the recent progress in material realization, the existence of stable and tunable junctions, the intrinsic magnetism, and the potential for higher-temperature performance we propose antiferromagnetic topological insulators as a new promising platform for electron quantum optics. |
Wednesday, March 16, 2022 3:36PM - 3:48PM |
Q72.00002: Topological Antiferromagnetic Spintronics: A case study of EuZnSb2 Niraj Aryal, Weiguo Yin Study of the interplay between band topology and magnetism is interesting and important for quantum spintronics applications. Last few years have witnessed a flurry of activities along this direction thanks to the successful prediction and discovery of several promising magnetic topological material candidates. However, in most of the strongly correlated magnetic topological systems discovered to date, especially the f-electron systems, the connection between the Dirac bands and magnetism is not obvious most of the times as the f-electrons lie far away from the Fermi level and do not contribute to the Dirac states. Here, we present a systematic study of a recently synthesized layered antiferromagnetic (AFM) square-net topological semimetal EuZnSb2 [1] and study its electronic structures and magnetic properties by employing the first-principles and effective Hamiltonian methods. We find that although the Dirac-like linear bands are present irrespective of the magnetic orderings, magnetism does play a subtle role in the topological classification and brings small but non-negligible changes in the gap size across the spectrum. Moreover, the broken symmetry introduced by the ordering of the magnetic moments is manifested in the bulk and surface electronic structures which in turn gives rise to distinct Berry curvature related transport properties. We discuss the experimental implications of our results and generalize our findings to other magnetic topological systems. [1] A. Wang et al., Phys. Rev. Research 2, 033462 (2020); 3, 029002 (2021). |
Wednesday, March 16, 2022 3:48PM - 4:00PM |
Q72.00003: Quantum sensing and imaging of a topological antiferromagnet Mn3Sn Gerald Q Yan, Senlei Li, Hanyi Li, Mengqi Huang, Yuxuan Xiao, Luke Wernert, Jeffrey A Brock, Eric E Fullerton, Hua Chen, Hailong Wang, Chunhui Rita Du Antiferromagnetic (AF) spintronics shows promise for next-generation computing technologies with improved density, stability, and energy efficiency in comparison with its ferromagnetic counterpart. The AF Weyl semimetal Mn3Sn possesses a topologically protected band structure, non-collinear magnetic order, and spontaneous time reversal symmetry breaking, enabling exceptionally large magneto-transport and magneto-thermal responses which may be exploited for a broad range of spintronics applications. Despite these potential benefits, direct access to the magnetic domains and magnetic spin behaviors in Mn3Sn remains a formidable challenge for the current state of the art. The major challenge results from the vanishingly small net magnetic moment of the Neél vector, which is difficult to access using existing magnetometry techniques. In this work, we use nitrogen-vacancy (NV) centers, optically active point defects in diamond, to image the local spin textures in polycrystalline Mn3Sn thin films on a sub-micron length scale. We also probe the underlying spin dynamics in Mn3Sn using NV relaxometry. Our results highlight the unique capabilities of NV centers as functional quantum sensors for investigating the magnetic properties of emergent topological antiferromagnets. |
Wednesday, March 16, 2022 4:00PM - 4:12PM |
Q72.00004: Strain tuning of the anomalous topological Hall effect at room temperature in bulk Mn3Sn Johanna Palmstrom, Nakheon Sung, Priscila Rosa, Sean Thomas, Eric D Bauer, Scott A Crooker, Ross D McDonald The Weyl semimetal Mn3Sn is a noncollinear antiferromagnet with a large intrinsic room temperature |
Wednesday, March 16, 2022 4:12PM - 4:24PM |
Q72.00005: Influence of Mn substitution on the topological metal Zr2Te2P Oladehin Olatunde, Ryan Baumbach, Kaya Wei, Yan Xin, Keke Feng, Jorge R Galeano-Cabral The ternary tetradymite Zr2Te2P was recently shown to be a simple example of Dirac nodal arc metal [1, 2], with nontrivial bands both above and below the Fermi energy. This invites further studies to access these novel bands (e.g., by tuning the Fermi energy) and to introduce additional interactions (e.g., by inserting magnetic ions). Here we present results from efforts to chemically substitute Mn into Zr2Te2P, where X-ray diffraction and chemical analysis (EDS) measurements show that single crystals form in expected structure and the Mn is present in concentrations of a few percent. TEM measurements additionally show that the Mn is evenly distributed inside the crystals, and that an additional P/Mn layer appears in the structure. Magnetization measurements reveal Curie Weiss behavior that is consistent with the Mn ions being in the divalent state. Fits to the data also indicate a ferromagnetic spin exchange along the c-axis and antiferromagnetic exchange in the ab plane, that is likely mediated by the RKKY interaction. At low temperatures we find evidence for a bulk disordered spin-glass phase, which is evident in the magnetic susceptibility, heat capacity, and electrical resistivity. |
Wednesday, March 16, 2022 4:24PM - 4:36PM |
Q72.00006: Centrosymmetric Lattice with a Frustrated Triangular Lanthanide Nets: GdAuAl4Ge2and TbAuAl4Ge2 Keke Feng, Ian Andreas Leahy, Kaya Wei, W. Lucas Nelson, Olatunde Oladehin, Minhyea Lee, Ryan Baumbach Similar to the centrosymmetric skyrmion lattice magnet Gd2PdSi3[1], the compounds LnAuAl4Ge2 (Ln = lanthanide) feature equilateral triangles of Ln ions within well separated planes [2]. This suggests that nontrivial magnetic states might also emerge in this family of materials. Here we focus on the Ln=Gd and Tb examples, where magnetization, heat capacity, and electrical transport measurements reveal complex magnetic ordering at low temperatures. In particular, the Gd compound shows three distinct transitions at T1,Gd = 17.8 K, T2,Gd = 15.6 K, and T3,Gd = 13.8 K, and Tb compound shows two distinct transitions at T1,Tb = 13.5 K, T2,Tb = 9.7 K. This multiplicity of the ordered states reveals the presence of competing magnetic order parameters. Evidence for magnetic frustration is also seen in the form of strong magnetic fluctuations at temperatures well above the ordering temperatures. Finally, complex temperature-magnetic field phase diagrams are observed, with similarities to other metallic skyrmion host materials. We will present detailed electronic/magnetic phase diagrams for these compounds, compare them to other centrosymmetric skyrmion lattice compounds, and discuss prospects for uncovering similar behavior in the family of materials. |
Wednesday, March 16, 2022 4:36PM - 4:48PM |
Q72.00007: Antiferromagnetism and semimetallicity in EuSb2 Jörn Bannies, Mohamed Oudah, Meigan C Aronson Antiferromagnetic topological insulators (AFM TIs) have recently attracted a lot of interest because the breaking of time-reversal symmetry gaps the topological surface state, which gives rise to exotic effects like the quantum anomalous Hall effect. This makes AFM TIs promising candidates for spintronics applications. Antiferromagnetic semimetals are the gapless counterparts of AFM TIs, and in contrast have received less attention. Here, we demonstrate that EuSb2 is a member of this material class. Using high-quality single crystals, we investigate this state by means of transport, magnetization, and specific heat. Despite the antiferromagnetic order that develops below 26 K, a large magnetoresistance is found at low temperatures, indicative of a semimetal. The robustness of the semimetallicity against magnetic order relates EuSb2 to the analog non-magnetic semimetal CaSb2. Supported by DFT calculations, we attribute the semimetallicity to the distorted Sb square-nets in both diantimonides. This is an important step towards a more comprehensive exploration of AFM topological semimetals. |
Wednesday, March 16, 2022 4:48PM - 5:00PM |
Q72.00008: Observation of ultrastrong coupling with substrate and layer number dependent Raman modes in MnBi2Te4 Gaomin Li, Xiaohua Wu, Yue Zhao, Jun Yan, Mingyuan Huang The intrinsic magnetic topological insulator MnBi2Te4 has attracted significant interest recently as a promising platform for exploring exotic quantum phenomena. Here we report that when atomically thin MnBi2Te4 is deposited on a substrate such as silicon oxide or gold, there is a very strong mechanical coupling between the atomic layer and the supporting substrate. Considering that the layer number is a critical variant for the nontrivial phases in MnBi2Te4, we also investigate the layer dependence of lattice vibrations in MnBi2Te4. By measuring the circularly polarized Raman spectra of 1-11 layers MnBi2Te4, we observe that the interlayer breathing modes exhibit blueshift while the intralayer Raman modes show redshift for thinner samples. In addition, we also investigate the degradation in MnBi2Te4 thin layers by Raman spectroscopy, and find that low-energy Raman features are very sensitive to air exposure. Our work provides a convenient path to identify the layer number and sample quality of MnBi2Te4. |
Wednesday, March 16, 2022 5:00PM - 5:12PM |
Q72.00009: Magnetic domain walls in antiferromagnetic topological insulator heterostructures Niall B Devlin We explore the emergence of spin-polarized flat bands at head-to-head domain walls (DWs) in topological insulator heterostructures with in-plane magnetization and interlayer antiferromagnetic coupling. We show in the framework of quantum well physics that, by tuning the width of a DW, one can control the functional form of the bound states appearing across it. Furthermore, we demonstrate the effect that the parity of the number of layers in a multilayer sample has on the electronic dispersion. The alignment of the magnetization vectors on the top and bottom surfaces of odd-layer samples affords particle-hole symmetry, leading to the presence of linearly dispersing topologically nontrivial states around E=0. By contrast, the lack of particle-hole symmetry in even-layer samples results in a gapped system, with spin-polarized flat bands appearing on either side of a band gap, with a characteristic energy well within terahertz energy scales. Such a system is a versatile platform for the development of spintronic devices and proposes one use in reconfigurable magnetic memory. |
Wednesday, March 16, 2022 5:12PM - 5:24PM |
Q72.00010: Magnetic field tuning of the valley population in the Weyl phase of Nd2Ir2O7 Itzik Kapon, Willem Rischau, Bastien Michon, Kai Wang, Bing Xu, Qiu Yang, Satoru Nakatsuji, Dirk Van Der Marel Materials hosting Dirac valleys serve as promising candidates for novel electronic devices. Valley polarization, the population control of distinguishable valleys, is yet the most formidable challenge in this area. The frustrated magnet Nd2Ir2O7, where strong correlations together with spin-orbit coupling play a crucial role, is predicted to be a Weyl semimetal and to host topological pairs of bulk Dirac-like valleys. Here we use an external magnetic field to manipulate the localized rare earth 4f moments coupled to the 5d electronic bands. Low energy optical spectroscopy reveals that a field of only a few teslas suffices to create charge compensating pockets of holes and electrons in different regions of momentum space, thus introducing a valley population shift that can be tuned with the field. This demonstrates that rare earth elements can act as boosters of an external magnetic field, making these materials good candidates for ``valleytronics" devices. |
Wednesday, March 16, 2022 5:24PM - 5:36PM |
Q72.00011: Strain-induced magnetic planar Hall effect in antiferromagnetic Nd2Ir2O7 thin film Jeongkeun Song, Tae Won Noh In topological magnetic materials, external magnetic field, Hext, couples with intrinsic magnetic structures, leading to complex topological magnetic behavior such as anomlaous and quantized hall effect. While most of studies have been focuesed on ferromagnetic materials, the progress on antiferromagnetic (AFM) materials is just at the beginning. due to their robustness of external perturbation and vanishingly small magnetization. Recently, the torque-magnetometry study on AFM Eu2Ir2O7 suggests that applying Hext in-plane direction on Eu2Ir2O7 can produce nonlinear magnetization MꞱ, which is orthogonal to the Hext [1]. Theoretically, such MꞱ could originated from higher magnetic ordering, octuople [1]. However, the further epxereimental study of octupolar orthongonal magnetization, MꞱo, remains elusive. Here, we present the study of MꞱo in AFM fully-strained Nd2Ir2O7 thin film using various magneto-transport technique. Nd2Ir2O7 belongs to one of All-in-All-out (AIAO) antiferromagnetic pyrochlore irdate family. With the epitaxial strain, Nd2Ir2O7 becomes metallic and the AIAO ordering expereience spin canting. Such canted AIAO are knwon as the addition of three spin clusters (Dipole, A2-octupole and T1-octupole) [2]. The generation of two octuopolar ordering creates non-vanishing Berry curvature and induces anomalous Hall effect. Moreover, using in-plane rotational transport measurement, we found that the two octupoles can induce MꞱo and affect in-plane anomalous and planar Hall effect in Nd2Ir2O7 thin film. Our work highlights on the interplay of strain, topology, and magnetism in antiferromagnetic materials. |
Wednesday, March 16, 2022 5:36PM - 5:48PM |
Q72.00012: 2D Electron Gas Subject to Inhomogeneous Magnetic Fields: Current Oscillations, the Role of Spin and Non-Landau Quantization Dominik Sidler, Michael Ruggenthaler, Vasilis Rokaj, Angel Rubio We demonstrate numerical and analytical results for a 2D electron gas in an inhomogeneous magnetic field. The coexistence of solid state and atomistic properties is caused by field induced localisation effects. In contrast to the paradigmatic Landau setting for homogeneous magnetic fields, we will demonstrate that the Zeeman (Spin) interaction becomes a highly relevant contribution, which gives rise to non-trivial orbital and spin currents. Resulting modifications of the Landau level structure and emerging density fluctuations are investigated. |
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