Bulletin of the American Physical Society
2024 APS March Meeting
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session Z04: Flat Band in Topological SemimetalsFocus

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Sponsoring Units: DMP Chair: Chandra Shekhar, Max Planck Institute for Chemical Physics of Solids; Turan Birol, University of Minnesota Room: L100D 
Friday, March 8, 2024 11:30AM  11:42AM 
Z04.00001: Electronic structure in the Dirac nodalline semimetals TaNiTe_{5} and TaPtTe_{5} Maximilian Daschner, Friedrich M Grosche, Ivan Kokanović Among the nodalline semimetals (NLSMs), Dirac nodal lines (DNLs) that are robust against spinorbit coupling (SOC) have been increasingly shown to exist in three and twodimensional systems, but rarely occur in (quasi) onedimensional materials. The latter can be found in twodimensional systems with inplane anisotropy [1], since additional crystalline symmetries such as mirror or nonsymmorphic symmetries are required to protect a nodal line band crossings [2]. A family of exfoliatable, strong inplane anisotropic, nonmagnetic, ternary transition semimetal tellurides, Tabased TaMTe_{5} (M=Ni, Pd, Pt) [1,3,4], has recently been shown to host nodal lines with fourfold degeneracy. 
Friday, March 8, 2024 11:42AM  11:54AM 
Z04.00002: Second Harmonic Generation in Correlated Topological Semimetals Snehasish Nandy, JianXin Zhu Nonlinear responses have proved a powerful way to reveal, understand, and tune the wavefunction geometry and/or topology, driven by the recent discovery and engineering of quantum materials. On the other hand, the interplay between topology and electronic correlations may offer a rich avenue for discovering emergent quantum phenomena in condensed matter systems. In this work, we explore the role of electronic correlation on the nonlinear optical response, specifically, the second harmonic generation (SHG). We identify six distinct contributions (e.g., shift, injection, Berry curvature dipole) to the SHG within the quantum kinetic theory framework. Furthermore, we apply our analysis to the WeylHubbard system to explore the effect of electronelectron correlation on the various components of the SHG signal. Our study reveals the possible mechanisms for correlationdriven SHG enhancement, which have direct experimental consequences. 
Friday, March 8, 2024 11:54AM  12:30PM 
Z04.00003: Flat Bands and Correlated States in Frustrated Lattice Metals Invited Speaker: Joseph G Checkelsky The notion of an electronic flat band refers to a collectively degenerate set of quantum mechanical eigenstates in periodic solids. The vanishing kinetic energy of flat bands relative to the electronelectron interaction is expected to result in a variety of manybody quantum phases of matter. Here we present recent developments in realizing flat bands in transition elementbased frustrated lattice metals. We will present recent experiments in which a partial filling of a flat band is associated with correlated transport and thermodynamic responses. We will also comment on the potential role of band topology and prospects for using similar lattice and orbital engineering to realize new electronic phenomena. 
Friday, March 8, 2024 12:30PM  12:42PM 
Z04.00004: Tunable topological effects in Ga doped Mn_{3}Sn thin films M. Raju, Tomoya Higo, Daisuke NishioHamane, Collin L Broholm, Satoru Nakatsuji Mn_{3}X(X=Sn, Ga, Ge) antiferromagnetic (AFM) Weyl semimetals have attracted significant research due to their large Berry phase effects and potential for applications[1,2]. The temperature range for the antichiral magnetic phase with large topological effects varies for each of these materials, the highest temperature being the Neel temperature (T_{N}). Thin film forms of Mn_{3}Sn are routinely studied [3], however, in Mn_{3}Sn the antichiral magnetic phase has a limited temperature range (≈260420K). To fully exploit the device possibilities, ranging from AFM spintronics [13] to unconventional superconducting spintronics based on Mn_{3}X/superconductor structures [4], one needs to engineer these Mn_{3}X thin film systems maximizing the Berry phase effects over a wide temperature range. In this work we present sputtered Mn_{3}Sn_{1x}Ga_{x} thin films in which the antichiral magnetic phase of Mn_{3}Sn is systematically modified with Ga doping. Our detailed structural characterization of Mn_{3}Sn_{1x}Ga_{x} reveals a systematic linear variation of the lattice parameters between Mn_{3}Sn (for x=0) and Mn_{3}Ga (for x=1) satisfying Vegard’s law of a substitutional solid solution. Temperature dependent Hall effect and magnetization measurements confirm a giant enhancement of anomalous Hall conductivity over a wide temperature range (extending from »500K down to at least 10K), and a systematic enhancement of T_{N} (from ≈420K to ≈500K) with Ga addition. In conclusion, our work presents a route for engineering topological effects in Mn_{3}X systems. 
Friday, March 8, 2024 12:42PM  12:54PM 
Z04.00005: Revealing the anomalous Hall like behavior of Kagome ScV_{6}Sn_{6} Chandra Shekhar, Changjiang Yi, Avdhesh K Sharma, Sushmita Chandra, Premkumar Yanda, Subhajit Roychowdhury, Nitesh Kumar, Claudia Felser Compounds with Kagome lattice structure are known to exhibit nontrivial topology in electronic band structures, leading to several versatile quantum phenomena. One of them is the anomalous Hall like behavior in ScV_{6}Sn_{6}, a nonmagnetic charge density wave (CDW) compound. The measured value Hall conductivity is of the order of 10^{4} Ω^{1}cm^{1}, which is fully entangled with the CDW phase. With the help of external and internal pressures, we disentangled the anomalous Hall behavior from the CDW phase, where the CDW phase exhibited significant changes while the anomalous Hall behavior remained unchanged. 
Friday, March 8, 2024 12:54PM  1:30PM 
Z04.00006: Quantum phase transitions in 2D moiré Dirac materials Invited Speaker: Nikolaos Parthenios Moire materials provide a new opportunity for the investigation of quantum phase transitions in twodimensional Dirac systems due to unprecedented experimental control. In particular, the relative interaction can be tuned via a twist angle so that it is possible to overcome the critical interaction strength needed to induce a quantum phase transition for Dirac fermions. We study possible patterns for spontaneous symmetry breaking in a Dirac fermion model motivated by twisted bilayer graphene at charge neutrality. These include the spontaneous generation of a gap, but also of a splitting in energy or wave vector of the Dirac points. We employ a renormalisation group treatment and discuss quantum critical behavior for different numbers of fermion flavours such as spin or valley. 
Friday, March 8, 2024 1:30PM  1:42PM 
Z04.00007: Unraveling the mesoscale surface and electronic structure in Co3Sn2S2 Sudheer Anand Sreedhar, Robert Prater, Zihao Shen, Giuseppina Conti, Slavomir Nemsak, Aaron Bostwick, Christopher Jozwiak, Eli Rotenberg, Makoto Hashimoto, Donghui Lu, Valentin Taufour, Sergey Y Savrasov, Inna M Vishik Co3Sn2S2 is a Magnetic Weyl Semimetal with multiple mesoscale cleave terminations for its crystal. These terminations have been observed to alter the topological surface states that connect the Weyl points. As a surface senstitive probe, photoemissionbased methods are uniquely suited to studying electronic, chemical and atomic structure on the same mesoscales. Using microfocused synchrotron photoemission, we identify signatures of different surface terminations in angleresolved photemission, xray photoemission and photoelectron diffraction spectroscopies. This multitechnique approach for connecting surfacve atomic and electronicstructure is broadly applicable to any material with characteristic surface electronic structure that depends on variable surface chemistry. 
Friday, March 8, 2024 1:42PM  1:54PM 
Z04.00008: Terahertz spectroscopy of the Dirac semimetal SrIrO_{3} Robert J Vukelich, Theodore R Walker, Shabnam Forutan, Mohan Giri, Tanzila Tasnim, Gaurab Rimal, Ryan B Comes, David J Hilton We use terahertz time domain spectroscopy on molecular beam epitaxially grown SrIrO_{3} on a GdScO_{3} substrate to study the terahertz conductivity from 6.5 K to 290 K. SrIrO_{3} is of interest because the band structure has a lifted Diraclike cone at the U point in DFT calculations and ARPES data, with an estimated gap calculated to be 5 meV (1.2 THz) when grown on a lattice matched substrate. Lattice matching of SrIrO_{3} can be achieved by growth on a GdScO_{3} substrate, where the strain due to lattice mismatch is negligible. Using terahertz time domain spectroscopy allows us to directly measure the band gap at the U point.. In addition, we use near infrared pumpTHz probe was used to study relaxation times of the lattice and electrons from 6.5 K to 50 K and use the twotemperature to model our results. 
Friday, March 8, 2024 1:54PM  2:06PM 
Z04.00009: Terahertz sensing based on layered topological semimetal Tairan Xi, Haotian Jiang, Yuchen Gu, Yulu Mao, Yangchen He, Daniel Rhodes, Daniel W Van Der Weide, Ying Wang, Jun Xiao The emergent atomically thin layered materials enable the unique control of new phases of matter for highperformance electronics and optoelectronics. One remarkable example is the recent discovered nonlinear Hall effect (NLHE) in topological semimetals, which is mediated by their diverging quantum geometrical properties [13]. It dictates a nontrivial secondorder transverse current can be induced by an oscillating electric field, greatly enhanced by large Berry curvature dipoles at the band edges. This effect serves as a measure of the topological attributes inherent in quantum materials. 
Friday, March 8, 2024 2:06PM  2:18PM 
Z04.00010: Highly mobile electrondriven transport in Dirac semimetallic oxide BiRe_{2}O_{6} Premakumar Yanda, Jorge CardenasGamboa, Inigo Robredo, Horst Borrmann, Maia Vergniory, Chandra Shekhar, Claudia Felser 5d transition metal oxides provide a fertile playground to explore new phenomena resulting from the interplay between topology, spinorbit, and electronelectron correlations. To date, however, limited studies of topological properties exist due to the difficulty in synthesizing single crystals of these oxides. Here, I will present magnetotransport and quantum oscillations study on highquality single crystals of Dirac semimetallic oxide BiRe_{2}O_{6}. It crystallizes in a monoclinic structure with space group C2/c (SG#15) and is a Pauli paramagnetic. Intriguingly, it exhibits large positive magnetoresistance of 110^{3} % at 2 K. Unlike other topological semimetals that show large MR, it evidences high electron carrier density and mobility of 0.510^{22} cm^{−3} and 110^{3} cm^{2} V^{1} s^{1}, respectively. Moreover, analysis of de Haas–van Alphen oscillation measurements and band structure calculations reveals the Fermi surface comprising of multiple pockets with small effective masses. Our findings may trigger to study of novel phenomena of correlated Dirac electrons in topological materials based on oxides. 
Friday, March 8, 2024 2:18PM  2:30PM 
Z04.00011: Sb_{1−x}As_{x} and Bi_{1−x}As_{x} alloys as Topological Weyl semimetals Muhammad Zubair, Shoaib Khalid, Dai Q Ho, Anderson Janotti Weyl semimetal (WSM) phase in antimony arsenic Sb_{1x}As_{x} alloys and bismuth arsenic Bi_{1x}As_{x} alloys are investigated using density functional theory, varying atomic composition, and structure arrangements. We find WSM states in all As concentrations in SbAs alloys, and for three As concentrations (x=0.5, 0.67, and x=0.83) in BiAs alloys with specific inversion symmetry broken. The Weyl points are located very close to the Fermi level in all compositions, facilitating their observation in experiments and suggesting that they could be characterized by analyzing surface and bulk transport properties. The presence of Fermi arcs also verifies the Weyl semimetal phase in SbAs and BiAs alloys. There is a total of 12 Weyl points located in the Brillouin zone for each composition. The chirality of these points shows that 6 Weyl points are the source and 6 Weyl points are the sink of Berry curvature. Our calculations also show that the surface bands reside within the bulk band gap. Our results illustrate the importance of composition and structure arrangement for determining the Weyl semimetal phase in the Sb_{1x}As_{x} and Bi_{1x}As_{x} alloys. 
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