Bulletin of the American Physical Society
2024 APS March Meeting
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session B03: Charge Density Wave and Phonons in Topological MaterialsFocus

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Sponsoring Units: DMP Chair: Min Gu Kang, Cornell University Room: L100C 
Monday, March 4, 2024 11:30AM  12:06PM 
B03.00001: Progress in Understanding the Charge Density Wave in ScV_{6}Sn_{6} Invited Speaker: David Mandrus Kagome metals are exciting flat band systems that often combine nontrivial topology with correlated electron physics. For example, the HfFe_{6}Ge_{6} (166) family of materials has been intensively investigated for their intertwined magnetism and topology. Recently, a charge density wave (CDW) was discovered in the 166 compound ScV_{6}Sn_{6} [1]. This prompted an intense investigation of this sytem over the past months. In this talk, I will review our current understanding of the CDW in ScV_{6}Sn_{6} and will also discuss similarities and differences between ScV_{6}Sn_{6} and 135 materials such as CsV_{3}Sb_{5}. 
Monday, March 4, 2024 12:06PM  12:18PM 
B03.00002: Visualizing electronic nematicity tunable by magnetic field in epitaxial Kagome magnet FeSn films Basu D Oli, Huimin Zhang, Qiang Zou, Lian Li Kagome lattice, a twodimensional hexagonal network of cornersharing triangles, hosts a plethora of quantum states arising from the interplay of topology, spinorbit coupling, and electron correlations. In this work, we report symmetrybreaking electronic orders tunable by an applied magnetic field in a model Kagome magnet FeSn consisting of alternating stacks of twodimensional Fe_{3}Sn Kagome and Sn_{2} honeycomb layers. On the Fe_{3}Sn layer terminated FeSn thin films epitaxially grown on SrTiO_{3}(111) substrates by MBE, we observed trimerization of the Kagome lattice using scanning tunneling microscopy/spectroscopy, breaking its sixfold rotational symmetry while preserving the translational symmetry. Such a trimerized Kagome lattice shows an energydependent contrast reversal in dI/dV maps, which is significantly enhanced by bound states induced by Sn vacancy defects. This trimerized Kagome lattice also exhibits stripe modulations that are energydependent and tunable by an applied inplane magnetic field, indicating symmetrybreaking nematicity from the entangled magnetic and charge degrees of freedom in antiferromagnet FeSn [Nat Commun 14, 6167 (2023)]. 
Monday, March 4, 2024 12:18PM  12:30PM 
B03.00003: Tuning of electron pairing by uniaxial strain in kagome lattices Miguel A Mojarro, Sergio E Ulloa Unique topological and correlated phases arise in kagome lattices associated with Dirac fermions and flat dispersions in the energy spectrum [1]. In this work, we study the interplay of attractive electron interactions and topological states in strained kagome lattices via a Hubbard Hamiltonian. It has been shown that the system is driven into a charge density wave state beyond a critical attractive interaction U_{c} in a meanfield approximation [2]. We study the tunability of U_{c} employing uniaxial strains and doping levels and find interesting different phases as these physical parameters change. As uniaxial strain breaks the C_{3 }symmetry of the lattice, we see the onset of a charge density wave ground state even for weak attractive interaction. In the presence of spinorbit interaction, the system changes from a quantum spin Hall state to a charge density wave at U_{c} for 1/3 and 2/3 filling, signaling topological phase transitions. We study the stability of these results beyond the meanfield with Density Matrix Renormalization Group calculations. This work illustrates how electronic correlations and singleparticle topological structures compete to create fascinating correlated phases in kagome systems. 
Monday, March 4, 2024 12:30PM  12:42PM 
B03.00004: Exploring structural selfdual twisted kagome metamaterials Pegah Azizi, Siddhartha Sarkar, Kai Sun, Stefano Gonella Fragile topological states of matter are known to lack the protective features usually associated with topology, resulting in relatively weak manifestations. The strength of these states is often influenced by the system's symmetry and boundaries, making them challenging to observe across various symmetries in phononics. These states are generally limited to specific symmetry classes and are not widely studied in the context of phononic media. However, in this study, we present a theoretical prediction of the emergence of fragile topological bands in a twisted kagome lattice in the selfdual configuration. We assume that the hinges are elastic, finitethickness ligaments that can store bending energy. The interplay between the edge modes in the bandgaps that bound the fragile topological states leads to the emergence of localized nontrivial corner modes at certain corners of a finite domain. This property qualifies the lattice as a secondorder topological insulator. To validate our findings, we conducted a series of experiments on a physical prototype using 3D Scanning Laser Doppler Vibrometry. Our results corroborate the theoretical predictions of the emergence of fragile topological states in this specific system, highlighting the potential of these states to manifest in unconventional configurations. 
Monday, March 4, 2024 12:42PM  1:18PM 
B03.00005: Tuning the electronphonon coupling in MX_{2} system Invited Speaker: Xiaohan Yao Whereas electronphonon scattering relaxes the electron’s momentum in metals, a perpetual exchange of momentum between phonons and electrons may conserve total momentum and lead to a coupled electronphonon liquid. In a previous study, we presented evidence of such an electronphonon liquid in NbGe_{2} [1], which could be a platform for observing electron hydrodynamics. Here we provide evidence on tuning the strength of electronphonon coupling by replacing Ge with Si and Nb with Ta. We combine de Haasvan Alphen (dHvA), electron transport, Raman scattering, and firstprinciples calculations in this MX_{2} topological semimetal family where M=Nb, Ta and X=Ge, Si [2]. Tuning electronphonon coupling increases the transport mobilities from nearly balanced to an order magnitude larger than quantum mobilities, with crystal structure or topology unchanged, and small differences in electron Fermi surface. Simultaneously, Raman scattering and firstprinciples calculations demonstrate a dominant phonondrag effect only in MGe2 compounds. Our study suggests phonondrag as a mechanism for achieving electronphonon hydrodynamics. 
Monday, March 4, 2024 1:18PM  1:30PM 
B03.00006: High field magnetotransport measurements of the Weyl semimetal and charge density wave compound TaTe_{4} Diego F Silvera Vega, Paula GiraldoGallo, Edwin HerreraVasco, Shalinee Chikara, Julián Rojas Castillo, José A Galvis The study of the coupling between topological states of matter and correlated states such as superconductivity or density waves in quantum materials has been an active field of research in experimental condensed matter physics in recent years. In this sense, TaTe_{4}, a representative of the family of transition metal tetrachalcogenides, appears as a perfect standpoint to study this kind of interplay, since it is a long knowncharge density wave system and a predicted Weyl semimetal. Here we present a detailed study of the electronic band structure of this compound, through a combination of high field magnetotransport measurements and density functional theory calculations. We provide evidence for the presence of Fermi surface sections not previously reported and analyze their connection with the predicted topological states for this compound. 
Monday, March 4, 2024 1:30PM  1:42PM 
B03.00007: InPlane Anisotropy in the Layered Topological Insulator Ta_{2}Ni_{3}Te_{5} Investigated via TEM and Polarized Raman Spectroscopy Kamal Harrison, Dylan A Jeff, Jonathan DeStefano, Olivia Peek, Akihiro Kushima, JiunHaw Chu, Humberto R Gutierrez, Saiful I Khondaker Ta_{2}M_{3}Te_{5}, (M = Pd, Ni) has emerged as a platform to study 2D topological insulators, which have unusual properties such as gapless surface states and spinmomentum locking. In particular, Ta_{2}Ni_{3}Te_{5} has been shown to host superconductivity under pressure and is predicted to host secondorder topology. In this work, we use TEM and polarized Raman spectroscopy (PRS) to study the anisotropic properties of exfoliated fewlayer Ta_{2}Ni_{3}Te_{5}. Electron diffraction and TEM imaging were used to probe the structural anisotropic response of the material. Angleresolved PRS was used to investigate the vibrational modes of the material, including their angular dependence, symmetries, and excitation energy dependence. 
Monday, March 4, 2024 1:42PM  1:54PM 
B03.00008: Identifying Raman modes in fewlayer WS_{2} using Polarized Raman Spectroscopy Sabin Gautam, Sabin Gautam, Sougata Mardanya, Joseph McBride, John Ackerman, Brian M Leonard, Sugata Chowdhury, Jifa Tian The anisotropic properties of lowsymmetry 2D materials hold significant promise for nextgeneration electronics and optoelectronics. 2MWS_{2}, as a newly discovered topological superconductor, has attracted substantial interest in recent years. Yet, a comprehensive study of its anisotropic features and the corresponding Raman modes remains to be conducted. In this work, we delve into the Raman modes and their corresponding polarization dependence in 2MWS_{2} thin layers using Raman spectroscopy. Preliminary findings suggest that the intensity of Raman spectra for 2MWS_{2} layers amplifies inversely with sample thickness. Furthermore, a detailed analysis of the polarizationdependent Raman spectra, using two distinct laser excitations, allowed us to identify specific Raman modes, encompassing both A_{g} and B_{g}, in fewlayer 2MWS_{2}. A notable observation is that the different Raman modes demonstrate a clear anisotropic dependence on the laser wavelengths. This study deepens our insight into the anisotropic properties of 2MWS_{2} and highlights the pivotal role of laser wavelength in discerning its crystallographic orientation through Raman spectroscopy. 
Monday, March 4, 2024 1:54PM  2:06PM 
B03.00009: Witnessing topological spin textures in GdRu_{2}Ge_{2} centrosymmetric magnet Dasuni Rathnaweera, Thao T Tran, Michal J Winiarski Magnetic skyrmions are topologically protected spin swirls that are appreciated as a source of emergent electromagnetism. Their topological property and stable particle nature ensure skyrmion is a suitable candidate for lowpower spinbased technologies. Particularly in centrosymmetric systems, magnetic skyrmions are mainly driven by longrange RudermanKittelKasuyaYosida (RKKY) exchange interactions assisted by geometrically frustrated lattice frameworks. One such goldmine for skyrmions in centrosymmetric systems is the Gd square lattice. GdRu_{2}Si_{2} has recently been shown to host skyrmion lattice around T < 20 K and 2 T ≤ μ_{0}H ≤ 2.5 T.^{1} Herein, we studied GdRu_{2}Ge_{2} in order gain a deeper understanding of how increased spinorbit coupling in the Ge analog influences the formation of skyrmions. Results from magnetoentropic mapping, topological Hall effect, and heat capacity measurements suggest the formation of skyrmions. We performed density functional theory calculations on both GdRu_{2}Ge_{2} and GdRu_{2}Si_{2} to connect and contrast the relationships between the spinpolarized band structures of these materials and their skyrmion evolution. In this presentation, we will share the knowledge gained from this research from both experimental and theoretical perspectives. 
Monday, March 4, 2024 2:06PM  2:18PM 
B03.00010: Observation of domain wall in chiral antiferromagnet Mn_{3}Sn realized perpendicular magnetization Moeta Tsukamoto, Zhewen Xu, Tomoya Higo, Kouta Kondou, Kento Sasaki, Mihiro Asakura, Shoya Sakamoto, Pietro Gambardella, Shinji Miwa, Yoshichika Otani, Satoru Nakatsuji, Christian L Degen, Kensuke Kobayashi Magnetic domain wall in chiral antiferromagnet is an important factor in developing fast magnetic memory. The fast speed of the domain wall driven by the current guarantees the perpendicular magnetic memory to move fast, but the domain wall structure, the physics background, has yet to be revealed. Here, we observed the domain wall between perpendicular magnetization of cluster magnetic octupole in Mn_{3}Sn. Magnetic domains with over hundreds nm scale are observed using nanoscale scanning diamond magnetometry. Reconstructed magnetization is the most consistent with perpendicular polarization in all axes, including the tilted. The domain wall dominated by exchange interaction, not grain boundary, tells us the physical properties and the domain wall chirality. The magnetization axis in the domain wall rotates in the Kagome plane, which suggests that the magnetic octupole is preserved in the domain wall. The estimated domain wall width is much shorter than that of the bulk crystal. Detailed observation of the domain wall powerfully assists in developing materials and devices. Simultaneous revealing of the physical background contributes to understanding the nontrivial domain and spin structure. 
Monday, March 4, 2024 2:18PM  2:30PM 
B03.00011: Local structure and magnetic order in Magnetic Weyl semimetal Mn_{3}Sn TsungHan Yang, Yuanpeng Zhang, Vaclav Petricek, Xiaoping Wang, Jiaqiang Yan, Qiang Zhang Mn_{3}Sn, a noteworthy kagomelattice magnetic Weyl semimetal, has recently drawn considerable attention due to its intriguing properties. Even at room temperature, Mn_{3}Sn exhibits a large anomalous Hall effect, and the presence of magnetic Weyl fermions has been verified by angleresolved photoemission spectroscopy (ARPES) and magnetoresistance measurements. In this talk, I will present a comprehensive analysis of crystal structure, magnetic order, and atomic/magnetic pair distribution function analysis using Xray diffraction and neutron total scattering. Single crystal xray diffraction confirmed the hexagonal Mg_{3}Cdtype average structure at 293 K. The material undergoes a magnetic transition at T_{N1} ≈ 420 K to a 120° antiferromagnetic order (k=0) and forms an incommensurate helical magnetic order below T_{N2} ≈ 280 K with two propagation vectors, (0,0,0.0877) and (0,0,0.1049). These two propagation vectors exhibit opposite temperature dependence upon cooling, merging to one k vector and separating at lower temperatures. We further observed changes in the pair distribution function patterns associated with the commensurateincommensurate magnetic transition. This work uncovers the structural and magnetic correlations in local and average length scales and sheds light on understanding the spinlattice coupling in Mn_{3}Sn. 
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