Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B68: Magnetic Topological SemimetalsFocus Recordings Available
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Sponsoring Units: DMP Chair: Michihiro Hirata, Los Alamos National Lab Room: Hyatt Regency Hotel -Hyde Park B |
Monday, March 14, 2022 11:30AM - 12:06PM |
B68.00001: Tuning the interplay of magnetism and band topology in magnetic topological materials Invited Speaker: Ni Ni Magnetic topological material provides a great platform in discovering new topological states, such as the magnetic Weyl semimetal, axion insulators, Chern insulators, and the 3D quantum anomalous Hall (QAH) insulators. Since the interplay of magnetism and band topology determines their topological natures, understanding and manipulating the magnetism inside magnetic topological materials will be crucial[1,2]. In this talk, I will show that a continuous fine control of the magnetism in MnBi4Te7 topological insulator can be made by Sb doping. The first-principles calculations propose the band topology is modified and a type-I magnetic Weyl semimetal phase can be realized at intermediate dopings [3]. Furthermore, the magnetic state can be easily switched between antiferromagnetic and ferromagnetic by external pressure, resulting in one more knob to tune the magnetic topological state. Our study provides a rare tunable material platform to realize various topological states. |
Monday, March 14, 2022 12:06PM - 12:18PM |
B68.00002: Fermi Surface Evolution across the Weyl Nodes in MnBi2-xSbxTe4 Qianni Jiang, Johanna Palmstrom, John Singleton, Shalinee Chikara, David E Graf, Paul T Malinowski, Yue Shi, Aaron Wang, Zhong Lin, Chong Wang, Xiaodong Xu, Di Xiao, Jiun-Haw Chu A Weyl semimetal is a nontrivial topological phase whose energy bands cross at pairs of nodes with opposite chirality. A number of Weyl semimetals have been identified but typically possess multiple pairs of Weyl nodes and complicated Fermi pockets. Here, we report the quantum oscillation measurements of a Weyl semimetal candidate, MnBi2-xSbxTe4 in the Field-induced ferromagnetic (FM) phase. |
Monday, March 14, 2022 12:18PM - 12:30PM |
B68.00003: Topological Phases of MnA2X4 (A=Bi, Sb; X = Se, Te) under Magnetic Field Sugata Chowdhury, Kevin F Garrity, Francesca Tavazza The electronic topology and the associated topological protected states of MnBi2Te4 (MBT) and related materials bring excellent opportunities for developing next-generation devices. In this work, using density functional theory (DFT), we have studied the electronic properties and topological phases of the MBT family of intrinsic magnetic topological insulators in the presence of an external magnetic field. Our calculations reveal that the topological phase of bulk MnB2X4 (B = Sb, Bi; X=Se, Te) depends on the direction of the magnetic spins and the chemistry. Notably, the antiferromagnetic ground state of MnSb2Se4 is a trivial insulator, but in the presence of a strong external field, it becomes a nodal point or nodal line Weyl semimetal. Surprisingly, the antiferromagnetic ground state of MnSb2Te4 (MST) is a non-trivial insulator. MST is type-II Weyl semimetal when the applied magnetic field is in the z-direction, but becomes insulating with an inverted band gap when the external magnetic field is in-plane. Additionally, we have investigated the evolution of the topological phases of MBT as a fraction of Bi atoms are substituted with Sb. This work indicated how to manipulate the topological phase and electronics phase of the MBT family. All these stoichiometric magnetic materials are excellent candidates for spintronics devices. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B68.00004: Magnetism and Magneto-transport in the Kagome Antiferromagnet Weyl Metal Mn3Ge Gaurav Chaudhary, Olle Heinonen, Anton Burkov We perform classical Monte Carlo and stochastic Landau-Lifshitz-Gilbert simulations to study temperature dependent magnetism of Kagome antiferromagnet Weyl metal Mn3Ge and find that a long range chiral order sets in at a transition temperature well below the N{\'e}el temperature. Based on the crystalline symmetries, imposed by the chiral magnetic order, we argue for the presence of multiple iso-energetic Weyl nodes (nodes that are at same energy and with congruent Fermi surface around them) near chemical potential. Using the semi-classical Boltzmann equations, we show that the combined contribution to the net longitudinal magnetoconductance (LMC) and the planar Hall conductance (PHC) from tilted Weyl nodes can lead to signatures, qualitatively distinct from that of a single pair of Weyl nodes. In particular, we show that magnetic orders with different chiralities can give rise to different periods in LMC and PHC as a function of the in-plane magnetic field direction. This is ultimately related to differences in the symmetry-imposed constraints on the Weyl nodes. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B68.00005: A magnetic Weyl semimetallic phase in (111) oriented thin films of Eu2Ir2O7 Jak Chakhalian, Xiaoran Liu, Weida Wu, Daniel Haskel, John W Freeland, Philip J Ryan, Gilberto F Fabbris, Justin Wilson, Fangdi Wen, Lin Gu, Evguenia Karapetrova, Jong-Woo Kim, Mikhail S Kareev, Wenbo Ge, Shiang Fang, Jed Pixley The interplay between electronic interactions and strong spin-orbit coupling is expected to create a plethora of fascinating correlated topological states of quantum matter. Of particular interest are magnetic Weyl semimetals originally proposed in the pyrochlore iridates, which are only expected to reveal their topological nature in thin film form. To date, however, direct experimental demonstrations of these exotic phases remain elusive, due to the lack of usable single crystals and the insufficient quality of available films. Here, we report on the discovery of the long-sought magnetic Weyl semi-metallic phase in (111)-oriented Eu2Ir2O7 high-quality epitaxial thin films. The topological magnetic state shows an intrinsic anomalous Hall effect with colossal coercivity but vanishing net magnetization, which emerges below the onset of a peculiar magnetic phase with all-in-all-out antiferromagnetic ordering. The observed anomalous Hall conductivity arises from the non-zero Berry curvature emanated by Weyl node pairs near the Fermi level that act as sources and sinks of Berry flux, activated by broken cubic crystal symmetry at the top and bottom terminations of the thin film. In addition, we report on the oberavtion of chiral anomaly which is another landmark of Weyl fermions. |
Monday, March 14, 2022 12:54PM - 1:06PM |
B68.00006: Unique surface-state connection between Weyl and nodal ring fermions in ferromagnetic material Cs2MoCl6 Daisuke Hara Surface states connection for Weyl/Dirac/nodal line/ring semimetals have been widely studied, yet the one for systems with the coexistence of Weyl points and nodal line/ring lacks detailed research. We offer a ferromagnetic (FM) material as a candidate to study, and build k・p model for further analysis. In the case of topological materials with coexistence of Weyl nodes and nodal rings, the surface-state configuration and connection are unique yet have never been studied and discussed before. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B68.00007: Magnetic phase transitions and non-collinear spin structures in Weyl semimetal materials RAlSi (R=Ce, Nd, Sm) Xiaohan Yao, Hung-Yu Yang, Faranak Bahrami, Fazel Tafti Magnetic Weyl semimetals RAlSi (R = rare-earth) have a non-centrosymmetric crystal structure and a magnetic order, which makes them break both inversion symmetry and time-reversal symmetry. We focus on this material family and study their magnetic properties and spin structures using magnetic x-rays, susceptibility, neutron scattering, and heat capacity. Combining the experimental findings with first-principle DFT calculations, we find a gradual softening of the magnetic anisotropy from cerium to samarium compound. In parallel, the magnetic structures evolves from a commensurate in-plane order in CeAlSi, to an incommensurate out-of-plane order in NdAlSi, and a seemingly spiral order in SmAlSi. We will discuss the potential connection between these magnetic structures and the topological character of the band structure. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B68.00008: Logarithmic criticality in transverse thermoelectric conductivity of the ferromagnetic topological semimetal CoMnSb Hiroto Nakamura, Susumu Minami, Takahiro Tomita, Agustinus A Nugroho, Satoru Nakatsuji The transverse transport effect such as anomalous Hall and Nernst effect can be a good probe to indicate the topological texture in the band structure. Here, we report the results of our experimental studies on the magnetic, transport, and thermoelectric properties observed in our high-quality single crystal of the ferromagnetic metal CoMnSb. A sizable anomalous Hall conductivity σyx and transverse thermoelectric conductivity αyx are found experimentally and comparable in size to the values estimated from first-principles calculation. Our experiment further reveals that CoMnSb exhibits −T log T critical behavior in αyx(T), deviating from Fermi liquid behavior αyx ∼ T over a decade of temperature between 10 and 400 K, similar to ferromagnetic Weyl semimetal Co2MnGa and nodal-line semimetals Fe3X (X = Al, Ga). Our theoretical calculation for CoMnSb also predicts the −T log T behavior when the Fermi energy locates near the Weyl nodes in momentum space. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B68.00009: Raman scattering spectroscopy as a probe of magnetic Weyl semimetal. Natalia Drichko, Yuanyuan Xu, Predrag Nikolic, Satoru Nakatsuji, Takumi Ohtsuki, Yiming Qiu Experimental spectroscopic probe of electronic band structure close to the Fermi energy in order to prove an existence of Weyl nodes presents a challenge due to a need for high spectral resolution. Here we propose electronic Raman scattering (χ"(ω)) as a probe of Weyl nodes. In Weyl semimetal candidate Nd2Ir2O7 TRS breaking at TN=35 K is suggested to split a quadratic node into pairs of Weyl nodes. Experimentally, we observe an abrupt decrease of χ"(ω) below 20 meV at TN. Our calculations of Raman scattering response of Weyl semimetals suggest two components of scattering. In semimetals, electronic scattering by quasiparticles possessing finite life is proportional to the electronic DOS. In Weyl semimetals, an additional non-zero contribution of scattering specific to the Weyl nodes originates from Berry flux, which necessarily introduces a momentum shift, resulting in a χ"(ω)~ω2 frequency dependence. We discuss a correspondence of the low frequency χ"(ω) in Nd2Ir2O7 spectra to the theoretical predictions for Weyl semimetal. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B68.00010: Spin-polarized gap in the magnetic Weyl semimetal Co3Sn2S2 Jimin Zhao, Fei Sun, Tan Zhang, Changjiang Yi, Yanling Wu, Hui Zhao, Qing Wu, Youguo Shi, Hongming Weng, Jimin Zhao We report a unique type of gap in a magnetic Weyl semimetal Co3Sn2S2 where the electrons are spin polarized and preserve the spin-momentum locking feature of Weyl fermions. Such spin-polarized gaps are associated with the Weyl node annihilation, where a pair of Weyl nodes with opposite chirality touch each other at ∼210 meV above the Fermi energy. These are revealed by both time- and spin-resolved ultrafast spectroscopy experiments, combined with first-principles calculations. The spin-polarized gap opening is accompanied by a topological phase transition, and the gap magnitude exhibits an unconventional temperature dependence originated from the Weyl physics. Furthermore, we propose possible circularly polarized terahertz-midinfrared radiation from such a spin-polarized gap. Our results shed light on exploring the topological properties of excited states and endow application potentials for gapped materials based on chirality. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B68.00011: Anomalous electrical and thermal transport properties in the antiferromagnetic Weyl semimetals Mn$_3X$, $X$ = Sn, Ge. Takahiro Tomita, Muhammad Ikhlas, Susumu Minami, Taishi Chen, Mingxuan Fu, Shunichiro Kurosawa, Satoru Nakatsuji The large Berry-curvature-driven Anomalous Hall (ANE) and Nernst (ANE) effects of Mn3X (X= Sn, Ge) are theoretically examined and the calculated results agree well with the experiments as a function of the Fermi energy estimated by extra-Mn [Nature Commun. 12, 1-14 (2021), Nature Phys. 13, 1085-1090 (2017)]. These sizes of ANE (Syx = 0.6 ∼ 1.5 μV/K) are also large enough compared with the ordinary ferromagnets at the same net-magnetization. The anomalous Hall conductivity and the longitudinal conductivity are located within the intrinsic regime in the universal scaling relation between the longitudinal and Hall conductivity, indicating the topological origin in the electrical band structure. We also found that planer Hall effect accompanied by the positive longitudinal magneto-conductance in the magneto-transport measurements. The such phenomena are considered to be induced by the chiral anomaly corroborated with the magnetic Weyl semimetal due to the additional fact of the clear evidence of Weyl nodes, which is provided by angle-resolved photoemission spectroscopy (ARPES) and the corresponding theoretical band structure [Nature Mater.16, 1090-1095 (2017)]. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B68.00012: MnPO4: A Novel Candidate for Spintronics and Topological Applications SREEPARVATHY P C, Chia-Hsiu Hsu, Chanchal K Barman, Feng-Chuan Chuang, Aftab Alam Quantum materials, which host multiple quantum phenomena, attract the scientific world due to the fundamental and application point of view. We present a novel candidate MnPO4, recipient of requisite bulk and surface electronic structure properties for hosting two distinct quantum phenomena such as the non-trivial topological magnetic Weyl fermionic state and spin-gapeless semiconducting (SGS) nature, and hence MnPO4 turns to be a Composite quantum compound(CQC), which is very rare in condensed matter systems. A detailed investigation based on first principles density functional theory (DFT) reveals the SGS behaviour, where one spin channel shows the semiconducting nature and the other spin channel shows the zero band gap nature. Further, a drumhead like surface state originated from a nodal loop around Y high symmetry point in the Brillouin zone is identified. We have also traced the surface states emerged from the distinct Weyl nodes appeared in the presence of spin-orbit coupling. A large value of AHC of 1265 Ω-1 cm-1 is observed in our proposed compound at around -1.37 eV below the Fermi level. |
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