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 B43: Dirac and Weyl Semimetal: Magnetism and OpticsFocus
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Sponsoring Units: DMP Chair: Chaowei Hu, University of Washington, Seattle Room: Room 317 |
Monday, March 6, 2023 11:30AM - 12:06PM |
B43.00001: Nonlinear optical detection of dual ferromagnetism and antiferromagnetism in a magnetic Weyl semimetal Co3Sn2S2 Invited Speaker: Youngjun Ahn Identification of the magnetic ground state lies at the heart of realizing a magnetic Weyl semimetal and understanding its electronic band topology. In the archetypical magnetic Weyl semimetal Co3Sn2S2, there remains multiple puzzles about its magnetic state, as well as its magnetic domains and domain walls. In this presentation, I will present a set of rotational anisotropy (RA) second harmonic generation (SHG) studies of this centrosymmetric magnetic Weyl semimetal Co3Sn2S2. I will first show the leading order contribution to SHG in this compound is electric quadrupole. Then, by exploring temperature dependence of RA SHG patterns, I will show the presence of two magnetic phase transitions, one being a transition to the ferromagnetic state at TC,1 = 175 K for the out-of-plane component of magnetic moments and the other to the antiferromagnetic state at TC,2 = 120 K for the in-plane component. I will further illustrate that the intensity/orientation of the RA SHG scales with even/odd powers of order parameters, from which I can extract the critical exponents of both order parameters independently and consistently. Finally, I will comment on our RA SHG results in comparison with reflection magnetic circular dichroism results that are acquired on the same samples at the same experimental apparatus. Our investigations not only pin down the nature of the magnetism in Co3Sn2S2, but also extends capabilities of nonlinear optics to explore topological material systems preserving spatial inversion symmetry. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B43.00002: Giant surface second harmonic generation from layered topological type-II Dirac semimetal PdTe2 Syed Mohammed Faizanuddin, Ching-Hang Chien, Yao-Jui Chan, Si-Tong Liu, Chia-Nung Kuo, Chin Shuan Lue, Yu-Chieh Wen PdTe2 belongs to the ATe2 family (A = Pd, Pt, Ni) of layered, centrosymmetric, type-II Dirac semimetals (DSMs). With broken inversion symmetry at the surface, it hosts non-trivial topological surface states leading to peculiar light-matter interactions that are excellent for future optoelectronic and spintronic applications. In this work, we studied the surface-specific nonlinear optical property of PdTe2 via rotational-anisotropic second harmonic generation (SHG). To our best knowledge, this is the first experimental study of the surface-specific nonlinear optical property of type-II DSMs. Our measurements verify that SHG originates from the surface of PdTe2 by following its C3v surface symmetry via the electric-dipole contribution. Moreover, fresh crystal surfaces prepared by in situ cleavage exhibit a profound time-dependent evolution of the surface SHG by following surface oxidation kinetics. Quantitatively, we characterized all independent non-zero complex second-order surface nonlinear optical susceptibilities, χ(2)S,ijk, in the steady state as well as the transient state right after cleavage. The results indicate a giant magnitude of the out-of-plane χ(2)S. Detailed discussions about the electronic origin for giant χ(2)S and mechanisms causing the transient evolution of SHG will be given in the talk. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B43.00003: Magneto-scanning near-field optical microscopy in Dirac materials Makoto Tsuneto, Michael Dapolito, Zengyi Du, Lukas Wehmeier, Zijian Zhou, Wenjun Zheng, King Ping Wong, Shu Ping Lau, Xinzhong Chen, Suheng Xu, Qiang Li, Dmitri N Basov, Mengkun Liu Recently, Dirac materials have been drawing much attention as their gapless linear dispersion around band crossings (Dirac points) host various novel phenomena such as quantum magnetoresistance, chiral magnetic effect, anomalous thermoelectric effect, and so on. Among them, it has shown that surface plasmon polaritons (SPPs) in Dirac materials owing to their high mobility is less Ohmic loss compared to conventional noble metals like Au, Ag, etc., paving the way for controlling phonons beyond diffraction limit. In PtTe2, one of the Dirac semimetals, SPPs have been reported in several experimental studies using scanning near-field optical microscopy (SNOM)1,2. In this talk, we’ll show the results of our newly developed magneto-SNOM (m-SNOM) to investigate field dependence of plasmonic patterns and the tunability of the plasmon wavelength via magnetic field will be discussed.
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Monday, March 6, 2023 12:30PM - 12:42PM |
B43.00004: Magneto-optical responses of massive Dirac fermions derived from kagome magnet TbMn6Sn6 Kentaro Shoriki, Yoshihiro Okamura, Yusuke Nomura, Yukako Fujishiro, Aki Kitaori, Naoya Kanazawa, Ryotaro Arita, Yoshinori Tokura, Youtarou Takahashi Kagome-lattice magnets have been attracting increasing attention due to the emergence of massive Dirac fermions arising from the unique geometry of atomic lattice, potentially leading to realization of Chern insulator. The massive Dirac fermions are anticipated to show various electromagnetic phenomenon, such as the enhanced intrinsic anomalous Hall effect (AHE) and the quantized AHE, based on the Berry phase theory. The interband transition on massive Dirac bands, which is associated with the quantized AHE, is also expected to exhibit the universal magneto-optical resonance. However, the experimental observation of it is still challenging. In this study, we show magneto-optical responses originating from massive Dirac fermions in the kagome lattice magnet TbMn6Sn6. Infrared magneto-optical spectroscopy and first-principles calculations reveal a prominent resonance structure in the optical Hall conductivity. The observed spectra show quantitative agreements with the response function of massive Dirac fermions, establishing their general optical response. DC anomalous Hall conductivity arising from this Hall resonance exceeds 15 % of the quantized value e2/h per one kagome layer even at room temperature. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B43.00005: Scanning tunneling microscopy and spectroscopy studies of stanene on a Kagome antiferromagnet Zengle Huang, Zhiming Xu, Jiaqiang Yan, Brian C Sales, Yong Xu, Weida Wu The kagome antiferromagnet FeSn receives tremendous research attention due to the flat bands and Dirac fermions stemmed from the kagome lattice [1-3]. However, the spacing stanene layer, a single layer of tin atoms with honeycomb structure, has been neglected. It has been known to the community that stanene is an interesting 2-dimensional (2D) material proposed to be a large-gap quantum spin Hall insulator [4]. In this talk, we present the scanning tunneling microscopy/spectroscopy (STM/STS) studies of the stanene layer on the cleaved surface of FeSn. Combined with first-principle calculation and tight-binding modeling, our STM results suggest the surface stanene layer in FeSn is a highly tunable platform to explore 2D topological states of matter |
Monday, March 6, 2023 12:54PM - 1:06PM |
B43.00006: Correlating local chemistry with electronic structure in magnetic Weyl semimetal Co3Sn2S2 Sudheer Anand Sreedhar, Robert Prater, Vsevolod Ivanov, Antonio Rossi, Zihao Shen, Matthew C Staab, Ittai Sidilkover, Makoto Hashimoto, Donghui Lu, Giuseppina Conti, Slavomir Nemsak, Hadas Soifer, Sergey Y Savrasov, Valentin Taufour, Inna M Vishik Ultraviolet Angle-resolved photoemission spectroscopy (ARPES) is a surface sensitive technique, often probing only a few atomic layers below the surface, limited by the inelastic mean free path of the photoelectrons. Yet it remains a powerful and ubiquitous technique for direct visualization of electronic structure. This limitation often results in interesting interplay between local surface features and observed electronic structure. Importantly, topological quantum materials often have defining surface electronic structure which depends on the morphology of the exposed surface, necessitating simultaneous quantitative measurement of both the local surface chemistry and electronic structure. In this work we study the magnetic Weyl semimetal Co3Sn2S2 using ARPES and x-ray photoelectron spectroscopy (XPS) to establish how local surface chemistry, topological electronic structure, and strong electronic correlations interact with one another. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B43.00007: Current shunting effects in Cd3As2: a closer look at the topological-ferromagnet interface Nicholas A Blumenschein, Gregory Stephen, Karen E Grutter, Erick C Sadler, Jennifer E DeMell, Binghao Guo, Susanne Stemmer, Aubrey T Hanbicki, Adam L Friedman Topological materials, such as Cd3As2, are of great importance for next-generation computing systems where energy efficiency is paramount. For example, in spin-orbit torque magnetic random-access memory (SOT-MRAM), topological materials generate the spin-orbit torque necessary for magnetization switching of an adjacent magnetic layer. Current shunting at the ferromagnet-topological material interface can be detrimental for spin generation and overall SOT efficiency.1 Here, the current shunting effect is analyzed in permalloy- and gold-shunted Cd3As2 disk structures using angle-dependent magnetoresistance measurements. Shubnikov-de Haas oscillations and weak antilocalization effects are observed in the Cd3As2, and their presence is dampened upon incorporating a shunt onto the topological surface. Hakami-Larkin-Nagaoka and Tkachov-Hankiewicz models are used to evaluate the weak antilocalization.2,3 We confirm the effects of current shunting, and discuss its detriment to the efficiency of spin-based devices. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B43.00008: Anomalous Hall effect in an antiferromagnetic Weyl semimetal Yuxiang Gao, Shiming Lei, Yichen Zhang, Ming Yi, Emilia Morosan Large intrinsic anomalous Hall effect (AHE) has been considered evidence for Weyl nodes in magnetic Weyl semimetals. Compared to a normal ferromagnet, the AHE in Weyl semimetals originates from an effective field generated by the Weyl nodes, does not require a net magnetization, and should also persist in both the antiferromagnetic (AFM) and paramagnetic (PM) materials. So far, AHE has only been observed in a few AFM Weyl semimetals in magnetic field, including GdPtBi and Mn3Sn [1,2]. Two different AHE mechanisms have been proposed in these compounds [1,3], posing a general question: what are the AHE mechanisms for other AFM Weyl semimetals? |
Monday, March 6, 2023 1:30PM - 1:42PM |
B43.00009: Coupling of magnetism and Dirac fermions in YbMnX2 (X= Bi, Sb) Xiao Hu, Aashish Sapkota, Zhixiang Hu, Andrei T Savici, Alexander I Kolesnikov, John M Tranquada, Cedomir Petrovic, Igor A Zaliznyak Dirac and Weyl materials form a new class with unique properties. The interaction of Dirac fermions with other degrees of freedom leads to rich novel physics such as suppression of backscattering, impurity-induced resonant states and spin-polarized transport. The 112 ternary pnictogens A/RMnX2 (A= Ca, Sr; R= Yb, Eu; X= Bi, Sb) represent a particularly interesting family of Dirac materials, where the X layers hosting itinerant Dirac charge carriers are separated by strongly correlated, insulating antiferromagnetically ordered Mn-X layers. Both the inter-layer charge transport and the magnetic correlations between the Mn layers require that Dirac carriers are coupled to strongly-correlated Mn electrons. Hence, these materials provide an excellent opportunity to study the interaction of the conduction Dirac electrons with the local-moment magnetic Mn-X subsystem. We report inelastic neutron scattering measurements of magnetic excitations in YbMnBi2 and YbMnSb2. Our spin-wave analysis of the measured spectra allows to evaluate the intra- and inter-layer magnetic interaction and the spectral damping parameter, which are directly related to the coupling strength of Dirac fermions with local spin moments. Comparing our results with (Sr, Ca)MnBi2 where no indication of such coupling was found, allows to establish a general trend and helps to understand the strength and signatures of spin-Dirac fermion interaction in 112 Dirac materials. |
Monday, March 6, 2023 1:42PM - 1:54PM |
B43.00010: Direct observation of magnetic domains in rare-earth Weyl semimetal CeAlSi Bochao Xu, Jacob Franklin, Hung-Yu Yang, Fazel Tafti, Ilya Sochnikov Noncentrosymmetric Weyl semimetal CeAlSi exhibits ferromagnetic order below Tc ≈ 8.3K. Our early study shows that CeAlSi hosts a heterogenous state that consists of both stable and metastable ferromagnetic domains[1,2]. The exotic ferromagnetic states can be easily tuned using an external magnetic field due to the magnetoelastic effect and are closely related to the nontrivial electronic behaviors such as anomalous Hall effect and loop Hall effect[3]. In this work, we image the domain structure in CeAlSi with presence of an electric current in the sample. We show how the domains evolve with current and external field and discuss the coupling between the magnetic and the expected exotic electronic properties in CeAlSi. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B43.00011: Fragile flat-band surface state in ternary transition metal chalcogenides NbIrTe4 Jiabin Yu, Jiabin Yu, Giang Nguyen, Vanessa King, Mohamed Oudah, Hsiang-Hsi Kung, Meigan C Aronson, Andrea Damascelli, Lukas Muechler, Sarah Burke Ternary transition metal chalcogenides have been predicted to exhibit both topological Weyl semimetal properties in bulk crystals and quantum spin-hall insulating behavior in their monolayer form[1]. NbIrTe4 features an orthorhombic lattice structure (Td-phase) with broken inversion-symmetry similar to WTe2, with a topological band structure predicted to host 16 Weyl points in the Brillouin zone[2]. Here we present a recent scanning tunneling microscopy study of the surface electronic structure of NbIrTe4, together with ARPES measurements and DFT calculations. On one of the two inequivalent surfaces, we observe a prominent, narrow surface-state peak – with a FWHM around 10 mV – located about 8 meV below the Fermi level. This is in excellent agreement with our ARPES and DFT results, and corresponds to a flat band across the quasi-1D rows, as observed in previous ARPES experiments[3]. This sharp surface-state feature vanishes in tunnelling spectroscopy in areas where the top layer was shifted, disrupting the symmetry and polarization at the surface. [1] Liu, J., et al., Nano Lett. 2017, 17, 467
[2] Li, L. et al., Phys. Rev. B 2017, 96, 024106
[3] Ekahana, S. A. et al., Phys. Rev. B 2020 102, 085126
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Monday, March 6, 2023 2:06PM - 2:18PM |
B43.00012: Spin chirality induced large topological Hall effect in magnetic Weyl semimetallic Eu2Ir2O7 (111) epitaxial thin film MITHUN GHOSH Rare earth pyrochlore iridates RE2Ir2O7 are predicted to be magnetic Weyl semimetallic (WSM) materials in the presence of electron correlation (U) and spin-orbit coupling (l) . Here we have studied the magnetotransport properties of epitaxial Eu2Ir2O7 (111) thin film grown on YSZ by solid phase epitaxy technique. Low-temperature longitudinal resistivity (ρxx) data shows a power-law dependence on temperature, which signifies semimetallic charge transport. By varying the film thickness, the semimetallic charge transport is tuned to realize the predicted WSM phase. The Hall resistivity (ρxy) data exhibits an anomalous Hall effect (AHE), in the temperature range of 2–25 K. The intrinsic AHE is explained in terms momentum space Berry curvature of the Weyl nodes. In addition to the AHE an large topological Hall effect (THE) is observed in the temperature range of 2–5 K. Due to scalar spin chirality generated by the all-in-all-out (AIAO) non-coplanar spin structure of Ir4+ moments, the conduction electrons acquire a real-space Berry curvature and causes a large THE. Low-temperature (2–10 K) magnetoresistance (MR) data shows a non-hysteretic large negative MR, causes by reduction in scattering by the spin canting. For temperature of 15 K and above, MR shows hysteretic behavior up to the 90 K (metal-semimetal transition temperature). The hysteretic MR suggest magnetic field-induced domain imbalance of Ir4+ moments. |
Monday, March 6, 2023 2:18PM - 2:30PM |
B43.00013: Thermal chiral (gravitational) anomaly in antiferromagnetic topological Weyl semimetal NdAlSi Pardeep T Kumar, Mujeeb Ahmad, Md Shahin Alam, Xiaohan Yao, Fazel Tafti, Marcin Matusiak A chiral anomaly in condensed matter violates the chiral current conservation when an electric field (or thermal gradient) is applied parallel to a magnetic field. As a consequence, charge and energy pumping occurs between Weyl points of opposite chirality [1,2]. Here we report the emergence of such an effect in the antiferromagnetic Weyl semimetal NdAlSi, in which inversion as well as time-reversal symmetry are broken [3]. We observe that at low temperatures and in the high magnetic field, the electrical conductivity increases as a result of the chiral magnetic effect. Remarkably, the corresponding thermal conductivity also increases accordingly, providing experimental evidence for the thermal chiral (gravitational) anomaly in NdAlSi. Our results indicate that the chiral anomaly in Weyl semimetals significantly affects their properties on various levels.
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