Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 510)
Virtual (March 2022); Time Zone: Pacific Time
Session B37: New frontiers at the Intersection of strong correlations and topologyInvited

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Sponsoring Units: DCMP Chair: Silke BuehlerPaschen, Vienna University of Technology Room: Room 233 
Monday, March 6, 2023 11:30AM  12:06PM 
B37.00001: WeylKondo semimetals: From symmetrybased design to nonFermi liquid topology Invited Speaker: Haoyu Hu The interplay between interactions and topology in quantum materials is of extensive current interest. For metallic systems, whether and how electron correlations lead to topological states is an open and pressing problem. The notion of WeylKondo semimetal, introduced theoretically [1] and experimentally [2] concurrently, set the stage for progress. We have introduced a general framework, in which gapless topological states are driven by symmetry constraints on correlationinduced emergent excitations [3]. Along this direction, we have i) put forward a design principle to determine new WeylKondo semimetal phases and identify new correlated materials for their realization [4]; and ii) advanced the framework even when the Fermiliquid description breaks down, and put forward a nonFermi liquid topological semimetal phase [3] and a new topological semimetal quantum critical point [5]. Here, the multichannel Kondo effect or critical fluctuations of the local moments lead to both features of nonFermi liquid and characteristics of the nontrivial electronic topology [3,5]. Our work opens a new route to studying gapless topological phases in a broad range of strongly correlated materials. 
Monday, March 6, 2023 12:06PM  12:42PM 
B37.00002: Kondo Insulator YbB_{12}: Neutral Quasiparticles and Unconventional Charge Transport in Magnetic Fields of up to 75 T Invited Speaker: John Singleton YbB_{12} has attracted a great deal of attention over the past few years. At low temperatures it exhibits significant bulk fermionic contributions to both its heat capacity and thermal conductivity. In high magnetic fields, it shows both de Haasvan Alphen and Shubnikovde Haas oscillations suggestive of a threedimensional Fermi surface. Despite these ostensibly metallic properties, YbB_{12} is a Kondo insulator. Moreover, it behaves in a way that is at first sight counterintuitive: the higher its zerotemperature resistivity, the stronger the magnetic quantum oscillations. Having accumulated a large quantity of resistivity, Hall effect and magnetization data on YbB_{12} in magnetic fields of up to 75 T and temperatures down to 20 mK, a consistent picture is emerging of a Fermiliquidlike ensemble of electrically neutral quasiparticles that coexist with charge carriers that remain in a nonmetallic, or even “bad metallic” state. The neutral quasiparticles suffer successive Lifshitz transitions and undergo Landau quantization in applied magnetic fields; eventually they begin to die slowly after YbB_{12} passes through a KondoinsulatortoKondometal transition at around 45 T. The manner of their death and their other properties provide tight constraints for theories of neutral quasiparticles in mixedvalence systems. 
Monday, March 6, 2023 12:42PM  1:18PM 
B37.00003: Controlling electronic topology in WeylKondo semimetals Invited Speaker: Diego A Zocco The ability to control topological states at will holds great promise for its application in topological quantum devices. Heavy fermion compounds are well known for their excellent tunability, and provide an exceptional platform to explore the intersection of strong electronic correlations and electronic topology [1]. In this talk, I will focus on tuning experiments performed on heavy fermion semimetals in which Weyl nodes form in a setting of broken inversion and preserved timereversal symmetries. In Ce_{3}Bi_{4}Pd_{3}, which exemplifies the notion of WeylKondo semimetal (WKSM) [2,3], and in which a giant spontaneous Hall effect has been observed [4], we found that the application of relatively modest magnetic fields suppresses the topological signatures; we attribute this effect to the annihilation of Weyl nodes at a topological quantum phase transition [5]. CeRu_{4}Sn_{6} is another WKSM candidate material [6]. Interestingly, inelastic neutron scattering experiments revealed that the material is quantum critical without tuning [7]. I will present pressuretuning investigations of CeRu_{4}Sn_{6}, and discuss whether the WKSM state may nucleate out of quantum critical fluctuations [8]. 
Monday, March 6, 2023 1:18PM  1:54PM 
B37.00004: Spinpolarized imaging of strongly interacting fermions in the magnetic phases of Weyl candidate CeBi Invited Speaker: Yu Liu CeBi has a rich magnetic phase diagram and several predicted topological states that vary with magnetic phase. Here we focus on the ferrimagnetic and fullypolarized phases of CeBi, where our density functional theory (DFT) calculations predict several Weyl nodes near the Fermi level (E_{f}). We use spinpolarized scanning tunneling microscopy (SPSTM) and spectroscopy to image the surface magnetic order, and quasiparticle interference (QPI) imaging to quantify the band splitting of the ferrimagnetic and fully polarized phases with respect to the ground antiferromagnetic phase. In the ferrimagnetic phase, strong suppression of the surface spinpolarization at E_{f}, coincident with a Fano line shape in dI/dV, suggests the Bi p states partially Kondo screen the f magnetic moments, and this pf mixing causes strong Fermilevel band renormalization. The QPI measurements support p band flattening and ~100 meV splitting, suggesting a strongly interacting magnetic Weyl semimetal with robustly spaced Weyl nodes. In fully polarized CeBi, on the (001) surface we discover that the outer Bi 6p band splits by ~ 200 meV, which is large enough to overcome the hybridization gap and give rise to a magnetic Weyl state. Our SPSTM and QPI measurements in three magnetic phases of CeBi paint a consistent picture of a strongly interacting magnetic Weyl semimetal that can be driven between different topological phases with the external field. 
Monday, March 6, 2023 1:54PM  2:30PM 
B37.00005: Anomalous quasi particles in a kagome Weyl ferromagnet Invited Speaker: Y Soh It is widely thought that flatbands as well as Dirac and Weyl crossings can be supported in a kagomé layer. One model kagome system is Fe_{3}Sn_{2}, a ferromagnet with a high (~640 K) Curie temperature, which undergoes a first order spin reorientation around 120 K(1, 2). Our density functional theory (DFT) calculations predict Weyl nodes near the Fermi level E_{F} and electron pockets at the zone center(3). Magnetotransport of Fe_{3}Sn_{2} displays anomalous behaviour at temperatures below 80 K, where the spin reorientation is complete, such as tunability of the carrier density via magnetization(4) and a 3fold antisymmetric planar Hall effect(5). Until now, electron spectroscopy has not accounted for these interesting bulk properties: the angleresolved photoemission spectroscopy (ARPES) data published so far appear 6fold symmetric, with no sharp bands crossing E_{F}, and no studies showing obvious changes on cooling below 80 K. We report here on the use of microfocused ARPES to resolve quasiparticles near E_{F} sufficiently well to make contact with the anomalous bulk properties of Fe_{3}Sn_{2}._{ }With higher spatialresolving capability, we discover that Fe_{3}Sn_{2} has crystallographic twins for each of which ARPES is 3fold symmetric(6). Furthermore, the larger electron escape depth and higher energy resolution of laser ARPES combined with the ability to image a single domain, finally allow the observation of sharp quasiparticle bands crossing E_{F}. The sharpest band, appearing only below 80 K, cannot be reproduced by our DFT calculation suggesting that its origin is from strong correlations, a view reinforced by our additional finding that it and its neighbouring bands display marginal Fermi liquid behaviour. 
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