Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Y56: Topological: magnetism and spin-dependent phenomenaFocus
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Sponsoring Units: GMAG Chair: Valeria Lauter, Oak Ridge National Lab Room: Room 304 |
Friday, March 10, 2023 8:00AM - 8:12AM |
Y56.00001: Disorder-driven control of magnetism and topology in FeGe Temuujin Bayaraa, Sinead M Griffin Magnetic spin textures are both fundamentally intriguing and relevant to novel information storage and processing units, such as the racetrack memory which harnesses electromagnetism in solids to link topological properties to electronic transport phenomena. Recent results from our collaborators found evidence of 3D chiral spin textures, such as helical spins and skyrmions with different chirality and topological charge, stabilized in amorphous Fe–Ge thin films [1]. Here, we look at the emergence of chiral spin textures in structurally disordered FeGe by means of first-principles calculations and ab-initio molecular dynamics simulations. We investigate how the introduction of atomic-scale disorder affects the electronic, magnetic, and topological properties of FeGe. |
Friday, March 10, 2023 8:12AM - 8:48AM |
Y56.00002: Gate-tunable anomalous Hall effect in a 3D topological insulator/2D magnet van der Waals heterostructure Invited Speaker: Vishakha Gupta Experimental demonstrations of strong and controllable interactions between topological insulators and magnets are essential for identifying suitable material platforms that can realize and control topological magneto-electric effects. Here, we demonstrate advantages of samples made by mechanical stacking of exfoliated van der Waals materials for controlling the topological surface state of a three-dimensional topological (TI) insulator via interaction with an adjacent magnet layer. We assemble bilayers with pristine interfaces using exfoliated flakes of the TI BiSbTeSe2 and the magnet Cr2Ge2Te6, thereby avoiding problems caused by interdiffusion, disorder and spatial inhomogeneities that can affect interfaces made by top-down deposition methods. The samples exhibit an anomalous Hall effect (AHE) with abrupt hysteretic switching. For the first time in samples composed of a TI and a separate ferromagnetic layer, we demonstrate that the amplitude of the AHE can be tuned via gate voltage with a strong peak near the Dirac point. This is the signature expected for the AHE due to Berry curvature associated with an exchange gap induced by interaction between the topological surface state and an out-of-plane-oriented magnet. Our results establish all-vdW exfoliated topological insulator-2D systems as an excellent material platform for manipulating topological surface states and pave the way for improved control of topological magneto-electric effects in TI/magnet heterostructures. |
Friday, March 10, 2023 8:48AM - 9:00AM |
Y56.00003: Examination of the magnetic exchange interactions in transition-metal thiophosphates Alexandria R Alcantara, Christopher A Lane, Roxanne M Tutchton, Jason T Haraldsen 2D magnetic semiconductors have become of late interest due to their magneto-optical effects in lowered dimensionality. More specifically, CrPS4 has gained renewed attention due to its well-known features as an A-type AFM configuration prompting analysis and stability studies in its layered forms for use in scalable technology such as spintronic and optoelectronic devices. This study uses density functional theory (DFT) to report transition-metal thiophosphates (TMPS4, TM = Cr, Mn, Fe) by taking the well-studied 2D van der Waals magnet CrPS4 as a benchmark using experimentally determined values to confirm the parameters necessary to study TMPS4 bulk compounds. Using model Hamiltonian calculations through exact diagonalization, we compare the DFT calculations and report on the magnetic and electronic ground state orders, Heisenberg exchange interactions, and phase diagrams between each TMPS4 bulk compound. |
Friday, March 10, 2023 9:00AM - 9:12AM |
Y56.00004: STM imaging of nanoscale conducting and insulating domains with enhanced Rashba Islands in YbB6 Aaron J Coe, Zhihuai Zhu, Yang He, Dae-Jeong Kim, Zachary Fisk, Jennifer E Hoffman Hexaborides possess a diverse set of exotic properties, ranging from superconductivity to magnetism to non-trivial topology. However, the lack of a natural cleavage plane, as well as the surface-dependent polarity, have obscured their study. YbB6 is a predicted topological insulator, with some experimental evidence for conducting surface states of yet-unproven origin. Using scanning tunneling microscopy (STM) on the cleaved surface of YbB6, we image several coexisting terminations with distinct atomic structures, separated by sharp boundaries. Our spectroscopic measurements show significant band-bending between the terminations, resulting in both conducting and fully-gapped regions, which rule out a topologically-protected surface state. Yet we observe van Hove singularities on two terminations, suggesting the presence of Rashba spin-split quantum well states. We demonstrate the creation of enhanced Rashba islands within nanoscale charging rings using the local gating effect of the STM tip. Our study rules out the possibility that YbB6 is a strong topological insulator, but suggests the utility of YbB6 for creating spin-polarized p-n junctions at the atomic scale. |
Friday, March 10, 2023 9:12AM - 9:24AM Author not Attending |
Y56.00005: Colossal magnetoresistance in antiferromagnetic EuZn2P2 Matthew S Cook, Clement Girod, Sean Thomas, Daniele S Alves, Joe D Thompson, Priscila Rosa Matthew S. Cook, Clément Girod, Sean M. Thomas, Daniele S. M. Alves, Joe Thompson and, Priscila F. S. Rosa |
Friday, March 10, 2023 9:24AM - 9:36AM |
Y56.00006: Changes in magnetic properties of a 2D magnet in proximity to a 3D topological insulator Rakshit Jain, Vishakha Gupta, Husain F Alnaser, Amit Vashist, Vikram V Deshpande, Taylor D Sparks, Daniel C Ralph Interactions between three-dimensional topological insulators (TIs) and magnetism can induce exotic |
Friday, March 10, 2023 9:36AM - 9:48AM |
Y56.00007: Electric field-control of anisotropic magnetoresistance in a 3D topological insulator/ferrimagnetic insulator system Junseok Oh, Joseph N Sklenar, Yingjie Zhang, M. Benjamin Jungfleisch, Youngseok Kim, Gregory MacDougall, Matthew J Gilbert, Axel Hoffmann, Nadya Mason Recent research studies of magnetic topological insulators (TIs) such as MnBi2Te4 have led to the discovery of interesting phases of matter including quantum anomalous Hall insulators (QAHIs) and axion insulators [1]. On the other hand, utilizing magnetic proximity effect on TIs has also succeeded in producing QAHI states [2], making proximity-coupling another viable way to induce magnetic ordering in topological surface states. We experimentally observed anisotropic magnetoresistance (AMR) in 3D TI/ferrimagnetic insulator devices, Bi2Se3 on yttrium iron garnet (YIG) thin films at temperatures below 10K. The results indicate that the AMR in the exfoliated Bi2Se3 on YIG is related to the out-of-plane magnetic order induced on the TI surface, which rotates with the application of the external magnetic field in different orientations [3]. We further investigate the AMR's dependence on an electric field applied via a top oxide layer. The results reveal how the energy gap is tuned with both magnetic and electric fields. |
Friday, March 10, 2023 9:48AM - 10:00AM |
Y56.00008: Pumping of Orbital Magnetization By Spin Precession in Topological Magnets Yafei Ren, Wenqin Chen, Chong Wang, Ting Cao, Di Xiao It has been demonstrated that topological states are useful for controlling the spin dynamics of magnets. In this work, the reciprocal process, i.e. the responses of topological phases to dynamically precessing spins, is investigated. The heterostructure of a Z2 topological insulator and an easy-plane ferromagnet is our initial focus. Studied are the effects of spin precession on topological and magnetic properties. We will discuss the distinctions between edge and bulk contributions. We then turn to an antiferromagnetic topological insulator with parity-time symmetry. The effects of symmetry breaking by spin dynamics are investigated. Specifically, we reveal the physical manifestation of the hidden Yang's monopole at the point of topological phase transition. Experimental signatures of the monopole will be discussed. These results will benefit the dynamical control of the magnetic topological systems on demand. |
Friday, March 10, 2023 10:00AM - 10:12AM |
Y56.00009: All-Electrical Spin Pumping in Topological Insulators Marc Vila Tusell, Joel E Moore Generating spin currents without magnetic or optical methods is important for an easy integration of spintronics in electronic devices. The use of spin-orbit coupling to create and control spins with electric fields has consequently become a major topic of research. However, most mechanisms to convert charge to spin (such as the spin Hall effect) rely on applying a bias voltage, which inevitably produces energy losses in gapless systems. Here, we predict that a time-dependent change of the chemical potential in the surface states of a topological insulator or other spin-orbit coupled systems generates a non-equilibrium AC spin current, under standard assumptions about the spin current in crystals. This driving can be achieved with e.g. an AC gate voltage without any charge current. The resulting spin polarization is locked with the current direction and the magnitude of the current increases linearly with the chemical potential, indicating that larger doping of the surface states is favorable. We discuss how this effect can be measured in an experiment, either by an AC inverse spin Hall effect or by measuring the time evolution of the spin density with optical probes. Finally, since the effect is not only limited to topological insulators but to any Rashba-like system, we also show similar results for a Rashba 2DEG. Our work opens the door to efficiently use topological surface states for spin current generation. |
Friday, March 10, 2023 10:12AM - 10:24AM |
Y56.00010: Nature of the Dirac point magnon gap in the van der Waals Ferromagnet CrSiTe3 Travis J Williams, Mark D Lumsden, Andy Christianson, Seunghwan Do, Jiaqiang Yan The quasi-two-dimensional, semiconducting ferromagnet CrSiTe3 is an attractive candidate for spintronics applications and as a candidate to host bosonic topological excitations. Its relatively accessible transition temperature, large magnetic moment and the ability to grow large, clean single crystals makes this an ideal material for study. In this work, we perform detailed neutron scattering measurements of the magnetic excitations near the K-point in the ordered phase to determine the nature of the magnon gap. We find that the existence and magnitude of the gap is highly dependent on the model Hamiltonian and the experimental conditions, and we refine the bounds for the size of the gap. |
Friday, March 10, 2023 10:24AM - 10:36AM |
Y56.00011: Low-Power Optical Control of Two-Dimensional Magnets Ti Xie, Hasitha Suriya Arachchige, David G Mandrus, Cheng Gong A magnetic material, while dressed with different spin configurations, can host a variety of emergent phenomena such as chiral domain walls, skyrmions, and Majorana fermions. Traditional preparation of various spin textures in magnetic films by transforming an already established spin pattern demands intensive energy to cause spin flipping or domain wall motion. In contrast, engineering the phase transition kinetics potentially opens up new avenues to achieve desired spin configurations. The two-dimensional (2D) layered magnets, owing to the ultra-thinness, allow the magnetism control by various external stimuli, among which optical approaches promise non-destructive manipulation, both locally and globally. In this talk, I will introduce how we demonstrated a low-power optical control of 2D magnets. By perturbing the phase transition kinetics, we found that optically excited electrons are multiple orders of magnitudes more effective than electrostatically doped electrons in influencing magnetic domains. Our low-power optical operation paves the new avenue to efficiently engineer 2D spin textures for a plethora of emergent quantum phenomena. |
Friday, March 10, 2023 10:36AM - 10:48AM |
Y56.00012: Topological Magnon-Phonon Hybridization in 2D Antiferromagnets Shu Zhang Topological magnons, regarded as a promising candidate for efficient and stable transport channel, have been studied in various magnetic materials. Their topological structure can be even richer when taking into consideration other dynamic degrees of freedom in the system. We show that nontrivial topology can emerge in the hybridized excitations of magnons and phonons in a collinear antiferromagnet due to magnetoelastic coupling. Our theory has a general applicability to two-dimensional magnets, which is demonstrated by developing a continuum theory as the long-wavelength approximation to the tight-binding model. Here, the associated topological transport can be highly tunable as magnons are thermal excitations sensitive to magnetic field. In particular, the thermal Hall effect can exhibit sign switchings as we change the direction or the strength of the applied magnetic field, which may be of practical interest in spincaloritronic applications. We provide experimentally relevant predictions for the van der Waals antiferromagnet MnPS3 and bilayer FeCl2. |
Friday, March 10, 2023 10:48AM - 11:00AM |
Y56.00013: Concurrent Onset of Anomalous Hall Insulating state and Multifractal Wavefunction Structure in a Ferromagnetic Nodal Line Semimetal Ambikesh Gupta, Mathimalar Subramanian, Haim Beidenkopf, Nurit Avraham, Ady L Stern, Johannes Gooth, Claudia Felser, Stanislaw Galeski, Nitesh Kumar, Walter Schnelle, Felix von Oppen, Yotam Roet, Rafal Wawrzynczak Dirac nodes are prevalent in topological states of matter either in their boundary states, as in topological insulators, or in the bulk, as in topological semimetals. Gapping out those Dirac nodes gives rise to higher-order topological states of matter and exotic responses such as the anomalous quantum Hall effect and chiral anomaly. Here we demonstrate an alternative route for the realization of anomalous Hall insulators by gapping the nodal line band crossing in the ferromagnetic topological semimetal Fe3GeTe2 with disorder and electronic interactions. We find the simultaneous onset of diverse phenomenology below a common temperature scale of about 10K: a metal-to-insulator crossover in longitudinal resistivity; plateauing of the anomalous Hall conductivity; Formation of a sharp zero bias dip in local scanning tunneling spectroscopy; evolution of a multifractal structure of the surface electronic wavefunction. These concurrent observations suggest that when strong electronic interactions are present, the disorder can robustly promote the realization of topological responses rather than hamper their formation which commonly occurs in the non-interacting case. |
Friday, March 10, 2023 11:00AM - 11:12AM |
Y56.00014: Title: Temperature-dependent magneto-optical measurement of ferromagnetic kagome-lattice semimetal Co3Sn2S2 Arup Barua, Hengzhou Liu, Samuel Langelund Carrera, Deepak Sapkota, Zachary L Romestan, Soumya S Bhat, Varun Mapara, Dario A Arena, David G Mandrus, Aldo H Romero, Denis Karaiskaj Co3Sn2S2 is a Co-based shandite material with a ferromagnetic Curie temperature of around 175 K. The hexagonal lattice of the crystal forms a kagome network of Co atoms within the Co3Sn layer. The spin-up band crosses the Fermi level in the sample's band structure. We can create a ring structure by connecting the crossing points in 3D. This ring opens up more with spin-orbit interaction, resulting in a gap with anti-crossing lines. We studied temperature-dependent spin dynamics in ferromagnetic kagome-lattice semimetal Co3Sn2S2 via ultrafast time-resolved magneto-optic Kerr effect(TR-MOKE) up to 7T. |
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