Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R22: Topological Hall Effect and Transport Phenomena in Chiral MagnetsFocus

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Sponsoring Units: GMAG DMP Chair: Shulei Zhang, Argonne Natl Lab Room: LACC 402A 
Thursday, March 8, 2018 8:00AM  8:12AM 
R22.00001: Theory of Transport in Skyrmion Systems: Topological Hall Effect Tim McCormick, James Rowland, Nandini Trivedi, Mohit Randeria Skyrmion materials have attracted substantial recent interest, particularly for the effect of magnetic textures on the motion of itinerant electrons. Measurements of the Hall resistivity have usually been analyzed using a sum of the regular Hall effect and the anomalous Hall effect, and interpreting the remaining signal as a topological Hall effect. The topological Hall resistivity is then described using a simple model where the realspace Berry curvature of itinerant electrons is described as a uniform magnetic field with magnitude proportional to skyrmion density. In this talk, we will present a theory of electronic transport in systems with spinorbit coupled itinerant electrons coupled to chiral magnetic textures, where we analyze Berry curvature effects in real and momentumspace in both the semiclassical and quantum regimes. 
Thursday, March 8, 2018 8:12AM  8:24AM 
R22.00002: Topological Hall effect in weak coupling regime Kazuki Nakazawa, Manuel Bibes, Hiroshi Kohno Topological Hall effect (THE) arises from the exchange coupling M of conduction electrons to the magnetization texture having a scalar spin chirality. It is understood in terms of the effective magnetic field, B_{eff}, due to Berry phase in the strong coupling regime. In this case, electrons adjust their spin to the local magnetization, and B_{eff} is determined by the “local” magnetic structure. However, in the weak coupling regime, electrons fail in such adjustment and B_{eff} will be determined by a “nonlocal” spin chirality. 
Thursday, March 8, 2018 8:24AM  8:36AM 
R22.00003: Unexpectedly Large Skyrmion Topological Hall Effect near Room Temperature in Mesoscopic FeGe Maxime Leroux, Matthew Stolt, Song Jin, Douglas Pete, Charles Reichhardt, Boris Maiorov Magnetic skyrmions are nanometer sized topological spin structures proposed as building blocks of future memory devices with high density and low power consumption. Skyrmions give rise to a Topological Hall Effect (THE) that could be used for detection in memory bits. Even though the stabilization temperature of skyrmions in FeGe is near room temperature, its THE was assumed to be below detection limits because of the larger skyrmion size. I will present the first observation of skyrmion THE near room temperature (276 K, 3 °C) in a mesoscopic lamella extracted from a FeGe crystal with a Focused Ion Beam. This THE has an unexpectedly large magnitude (+5 nΩ.cm), and it unambiguously coincides with the skyrmion lattice revealed by neutron scattering. Hall Effect measurements also point to a reentrant magnetic phase adjacent to the skyrmion phase. We explain the large THE as result of a large normal Hall constant, revealing a new route to enhance THE, a requirement for electrical detection of skyrmions. 
Thursday, March 8, 2018 8:36AM  8:48AM 
R22.00004: Topological Hall Effect in Ultrathin SrRuO_{3} film Byungmin Sohn, Bongju Kim, Youngjae Choi, Tae Won Noh, Changyoung Kim With extensive interests on novel oxidebased devices such as electronics and spintronics, the 4d transition metal compounds have been considered as promising candidates. Especially, SrRuO_{3} is wellknown for an itinerant ferromagnetic metal with a high Curie temperature , leading to anomalous Hall effect (AHE) below . Owing to the intense study on Hall effect in SrRuO_{3} thin films, the mechanism of Hall effect has been wellestablished. Here, we observed extraordinary Hall effect in highquality SrRuO_{3} ultrathin films grown by pulsed laser deposition (PLD), which cannot be explained in terms of simple AHE. We claim that this extraordinary Hall effect can be understood as topological Hall effect, which occurs due to emergent electromagnetic field (EEMF) derived from Skyrmion spin texture. Moreover, the Skyrmion phase is extremely stable with sustaining large external magnetic field range, about 1 Tesla. We suggest that the large spin orbit coupling of Ru ions and the inversion symmetry breaking produce DzyaloshinskiiMoriya (DM) interaction and consequently the Skyrmion phase is formed in ultrathin SrRuO_{3} film. 
Thursday, March 8, 2018 8:48AM  9:00AM 
R22.00005: Image Simulation of Magnetic Skyrmions on Oxygen Deficient EuO_{1x }with Spinpolarized Scanning Tunneling Microscopy Aaron Wang, TeYu Chien Magnetic skyrmions are topologically protected nanometersized nontrivial spin textures. Here we present the simulation images of magnetic skyrmions with spinpolarized scanning tunneling microscopy (SPSTM) on EuO_{1x}. With the observed topological hall effect (THE), magnetic skyrmion is suspected to exist in EuO_{1x}. Other evidences point to the oxygen vacancies are closely related to this THE related magnetic topological states. Among the various techniques of probing skyrmions, SPSTM is one with direct imaging and high spatial resolution, capable of visualizing nonordered skymions, in contrast to the skyrmion lattice probed by neutron scattering. SPSTM has ferromagnetic or antiferromagnetic materials on the tip apex. The tunneling current is determined by the angle between the spin orientations of the tip apex and the sample surface. Through simulations, it is concluded that the inplane (with unknown spin orientation) and outofplane spin polarized tip scanning over various types of skyrmion textures could identify the existence of the skyrmions in EuO_{1x}. Furthermore, with the known inplane spin orientation, specific type of skyrmion can be determined. 
Thursday, March 8, 2018 9:00AM  9:12AM 
R22.00006: Numerical study of the electronic state and transport properties in a chiral soliton lattice Shun Okumura, Yasuyuki Kato, Yukitoshi Motome Chiral magnets often show interesting properties associated with their peculiar spin structures. A typical example is a chiral soliton lattice (CSL), which was found in a monoaxial chiral magnets CrNb_{3}S_{6} [1] and Yb(Ni_{1x}Cu_{x})_{3}Al_{9} [2]. These compounds show a helical spin spiral at zero field, and turn into the CSL in a magnetic field perpendicular to the helical axis. To clarify the electronic and transport properties in the CSL, it is crucial to take into account itinerant electrons; nevertheless, most of the previous studies were focused on localized spin models. Here, we investigate a minimal itinerant electron model, a onedimensional Kondo lattice model with the DzyaloshinskiiMoriya interaction, by Monte Carlo simulation and variational calculations. We show that the system exhibits nonlinear negative magnetoresistance in the CSL, which is closely related to the soliton density [3]. We also find that the periodicity of CSL can be locked at commensurate values dictated by the Fermi wave number, which suggests the possibility of spontaneous formation of the CSL even at zero field. 
Thursday, March 8, 2018 9:12AM  9:24AM 
R22.00007: Electrical magnetochiral effect induced by chiral spin fluctuations in MnSi Tomoyuki Yokouchi, Naoya Kanazawa, Akiko Kikkawa, Daisuke Morikawa, Kiyou Shibata, Takahisa Arima, Yasujiro Taguchi, Fumitaka Kagawa, Yoshinori Tokura Chirality of matter can give rise to unique responses in optics, electricity and magnetism. One such example is electrical magnetochiral effect (eMChE), which is directional nonlinear magnetotransport in proportion to an innerproduct of B and j [1,2]. Electrical magnetochiral effect in magnetic materials has not been reported so far. 
Thursday, March 8, 2018 9:24AM  9:36AM 
R22.00008: Numerical investigations of itinerant electrons coupled to skyrmion lattice Yuanda Liao, ZiYang Meng, Xiaopeng Li We investigate the properties of fermions coupled to skyrmion lattice in frustrated spin system with Selflearning MonteCarlo (SLMC) and Kernel Polynomial Method (KPM). SLMC captures the lowenergy physics of the coupled system and provides global update of spin configurations, and KPM is an efficient algorithm to calculate spectral quantities and various correlation functions of the itinerant electrons. By means of such unbiased numerical tools, the novel spectral and transport properties of itinerant electrons in the presence of effective gauge field generated by the skyrmion lattice spin background, are revealed with high accuracy. 
Thursday, March 8, 2018 9:36AM  9:48AM 
R22.00009: Large Magnetothermopower in MnGe with topological spin texture Yukako Fujishiro, Naoya Kanazawa, Takahiro Shimojima, Asuka Nakamura, Kyoko Ishizaka, Takashi Koretsune, Ryotaro Arita, Atsushi Miyake, Hiroyuki Mitamura, Kazuto Akiba, Masashi Tokunaga, Shojiro Kimura, Satoshi Awaji, Shiogai Junichi, Atsushi Tsukazaki, Akiko Kikkawa, Yasujiro Taguchi, Yoshinori Tokura A topological spin texture—a threedimensional array of hedgehogs and antihedgehogs—shows up in a chiral magnet MnGe. Those hedgehogtype spin textures serve as “emergent” magnetic monopoles whose fluctuations critically affect charge transport phenomena. 
Thursday, March 8, 2018 9:48AM  10:00AM 
R22.00010: Topological Hall effect in spinorbit coupling TI thin film Jianxiao Zhang, ChaoXing Liu In this report, we examined the coexistence of SOCinduced intrinsic anomalous Hall effect and skyrmioninduced topological Hall effect in a TI thin film. Numerical Green's function transport calculation suggests the possibility of a reversed sign of transverse voltage due to the competence of these mechanisms. 
Thursday, March 8, 2018 10:00AM  10:12AM 
R22.00011: Skyrmion electrical detection with the use of threedimensional topological insulator / magnetic bilayers Dimitrios Andrikopoulos, Bart Soree In this work, we numerically investigate the effect of the magnetic skyrmion texture on the transport properties of the topological insulator surface state. It is shown that both Bloch and Nèel skyrmion textures interacting via proximityinduced exchange coupling with the surface state electrons, induce additional scattering on top of a homogeneous background ferromagnetic texture which can modify the conductance of the system. The change in conductance depends on the skyrmion size, the dimensions of the magnetic system and the exchange interaction strength. For the Nèel skyrmion, the result of the interaction strongly depends on the skyrmion number N_{sk} and the skyrmion helicity h. For both skyrmion types, significant change of the resistance can be achieved, which can be in the order of kΩ. 
Thursday, March 8, 2018 10:12AM  10:24AM 
R22.00012: Anomalous transverse response in Mn_{3}X (X=Sn, Ge) Zengwei Zhu, Xiaokang Li, Liangcai Xu, Linchao Ding, Jinhua Wang, Mingsong Shen, Xiufang Lu, Kamran Behnia In ferromagnets, there is an Anomalous Hall Effect (AHE) due to spontaneous magnetization. Recently, in a family of nonlinear antiferromagnets, Mn_{3}X (X=Sn, Ge), an unexpectedly large AHE has been detected and attributed to a nonvanishing Berry [13]. We present, a study of electric, thermoelectric and thermal transport in Mn_{3}X (X=Sn, Ge). The three anomalous transverse conductivities (Hall, Nernst, and RighiLeduc) were quantified. The thermal and electrical Hall conductivities respect the WiedemannFranz law over the whole temperature range of study in Mn_{3}Sn [4]. We also carried out a study of angledependent AHE shedding additional light to the origin of anomalous transverse flow and their link to the locus of the Weyl nodes. 
Thursday, March 8, 2018 10:24AM  10:36AM 
R22.00013: Magnon Hall effect in kagome antiferromagnets with DzyaloshinskiiMoriya interactions Pontus Laurell, Gregory Fiete We theoretically study magnetic properties of kagome antiferromagnets with both in and outofplane DzyaloshinskiiMoriya interactions, such as the iron jarosites and the recently introduced spin1/2 compound Nd_{3}Sb_{3}Mg_{2}O_{14}. At low temperatures these systems order in a 120 degree spin configuration canted out of plane, resulting in a noncoplanar order with finite scalar spin chirality. We derive an expression for the canting angle in the presence of applied magnetic fields. We also study the spin wave properties as a function of canting, generically finding topological magnon bands at nonzero canting. Finally we calculate the resulting thermal Hall conductivity, and show how it can be controlled using magnetic fields. 
Thursday, March 8, 2018 10:36AM  10:48AM 
R22.00014: Magnonmediated analog to the Edelstein effect in an antiferromagnet Bo Li, Alexander Mook, Alexey Kovalev In metallic and semiconducting materials, the Edelstein effect produces a nonzero average nonequilibrium spatially homogeneous spin polarization by applied external electric field due to the imbalance of spin relaxation time of system with spin degeneracy lift by spinorbital coupling (SOC). For magnons, the DzyaloshiniskiiMoriya interaction (DMI) can play similar role to the SOC in a semiconductor and it can result in a nonequilibrium spatially homogeneous spin polarization in collinear and noncollinear insulating antiferromagnets under a temperature gradient. Using the linear response theory, we theoretically predict that by applying a temperature gradient to insulating antiferromagnet with spin nonconserving Hamiltonian, one can produce homogeneous spin accumulation mediated by magnons. We applied our theory to honeycomb, kagome, and pyrochlore collinear and noncollinear antiferromagnets. This prediction can be applied as a new way to generate spin currents in antiferromagnetic spintronic devices. 
Thursday, March 8, 2018 10:48AM  11:00AM 
R22.00015: Photonic orbital angular momentum transfer and magnetic skyrmion rotation Wenrui Yang, Huanhuan Yang, Yunshan Cao, Peng Yan Magnetic skyrmions are chiral quasiparticles that show promise for future spintronic applications such as 
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