Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E49: Strongly Correlated Topological MetalsInvited Live

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Sponsoring Units: DCMP Chair: Subir Sachdev, Harvard University 
Tuesday, March 16, 2021 8:00AM  8:36AM Live 
E49.00001: Extreme topological response in a nonmagnetic WeylKondo semimetal Invited Speaker: Silke BuehlerPaschen The interplay of topology and strong electron correlations is emerging as a new frontier in quantum science; it is expected to bring forth exotic phases and excitations [1], possibly through enhanced quantum fluctuations [2]. Heavy fermion systems provide an ideal setting to explore this new regime: The Kondo interaction implements extreme correlation strength and representatives with strong spinorbit coupling exist. We have recently discovered Weyl semimetal behavior in the noncentrosymmetric material Ce_{3}Bi_{4}Pd_{3} [3,4], a sister compound of the canonical Kondo insulator Ce_{3}Bi_{4}Pt_{3}, concurrently with the theoretical development of such a Kondodriven phase [5,6]. Ce_{3}Bi_{4}Pd_{3} has a Kondo temperature of 13 K [3] and remains paramagnetic down to at least 250 mK [4]. Our most striking observation is a giant spontaneous (zerofield) Hall effect, and an associated eveninfield Hall component, which provide direct evidence of Berry curvature singularities in close vicinity of the Fermi level [4]. These characteristics of Weyl physics develop only in the Kondo coherent state, and are thus manifestly correlation driven. The application of large magnetic fields leads to an annihilation of the Weyl nodes at a first critical field, and to the metallization of the system at a second one, featuring quantum criticality [7]. 
Tuesday, March 16, 2021 8:36AM  9:12AM Live 
E49.00002: WeylKondo Semimetal  How Strong Correlations Intersect with Electronic Topology Invited Speaker: Qimiao Si Strong correlations in metals are known to yield a rich variety of quantum phases. Whether and how they also drive electronic topology is of considerable current interest and, yet, a largely open question. A promising setting arises in heavy fermion systems, which may feature not only strong correlations but also a large spinorbit coupling. Recently, a WeylKondo semimetal phase has been concurrently discovered in theoretical [1] and experimental [2] studies. The theoretical work was carried out in a Kondo lattice model that is timereversal invariant but inversionsymmetry breaking. The nonsymmorphic spacegroup symmetry and strong correlations cooperate to produce Weyl nodal excitations with highly reduced velocity as well as to pin the resulting Weyl nodes to the Fermi energy. In this talk, I will present these theoretical developments, describe in some detail the interplay between the Kondo interaction and spacegroup symmetry [3] and, motivated by recent highfield experiments on Ce3Bi4Pd3 [4], the control of the Weyl nodes [5]. I will also touch upon the results on other Kondo lattice models, which are constructed based on spacegroup symmetry constraints. Finally, I will discuss the enrichment of our results for the strong correlation physics, in the form of a global phase diagram, of heavy fermion metals [6]. 
Tuesday, March 16, 2021 9:12AM  9:48AM Live 
E49.00003: Transport in the Magnetic Weyl Semimetal Y_{2}Ir_{2}O_{7} Invited Speaker: Arthur Ramirez Despite their name, the behavior of undoped Weyl Semimetals (WSMs) should be semiconductinglike, with resistivity exhibiting a negative temperature coefficient, dρ/dT < 0. Unlike semiconductors (either intrinsic or those exhibiting variable range hopping) however, the density of states in WSMs will exhibit power law behavior at points or lines in the Brillouin zone, which leads to inverse power law behavior in ρ(T). We show that an inverse quartic law, as predicted for charged impurity scattering, is consistent with existing data on the rareearth iridate pyrochlores, R_{2}Ir_{2}O_{7} as a limiting form. We also show that for R = Y, ρ ∝ T^{4} over four orders of magnitude in ρ, extending into a temperature range where k_{F}l << 1, suggesting behavior of a “bad” WSM. A picture of localization into deep potential wells with strong electron correlations is supported by thermopower data on the same samples. Transport and thermodynamic data will also be presented for different pyrochlore lattice systems of the general form Li_{2}M_{2}O_{7}, where M = Ir, Os, Ru, and Rh, for which power law behavior is also observed. 
Tuesday, March 16, 2021 9:48AM  10:24AM Live 
E49.00004: Spectroscopic studies of candidate topological Kondo insulators and Weyl semimetals Invited Speaker: Steffen Wirth SmB_{6} has been proposed a topological Kondo insulator with nontrivial surface states inside a bulk hybridization gap. Experimentally, hybridization between localized 4f and conduction band states at low T is well established [1]. Using STM, we performed local measurements on well identified, atomically flat, unreconstructed surfaces [2]. Spectroscopy down to 0.35 K revealed states around –6 mV and –2 mV within the hybridization gap, which are dominated by surface contributions [3]. Introducing magnetic impurities in samples (Sm_{1x}R_{x})B_{6} with R = Gd represses the surface states on a much larger length scale compared to nonmagnetic impurities R = Y [4]. The influence of Sm vacancies on the surface states as well as surface manipulation by focused ion beam (FIB) will also be discussed in detail. 
Tuesday, March 16, 2021 10:24AM  11:00AM Live 
E49.00005: From Trivial Kondo Insulator Ce_{3}Pt_{3}Bi_{4} to Topological Nodalline Semimetal Ce_{3}Pd_{3}Bi_{4} Invited Speaker: Chao Cao Using the density functional theory combined with dynamical meanfield theory, we have performed systematic study of the electronic structure and its band topology properties of Ce_{3}Pt_{3}Bi_{4} and Ce_{3}Pd_{3}Bi_{4}. At high temperatures (∼290 K), the electronic structures of both compounds resemble the opencore 4f density functional calculation results. For Ce_{3}Pt_{3}Bi_{4}, clear hybridization gap can be observed below 72 K, and its coherent momentumresolved spectral function below 18 K exhibits an topologically trivial indirect gap of ∼6 meV and resembles density functional band structure with itinerant 4f state. For Ce_{3}Pd_{3}Bi_{4}, no clear hybridization gap can be observed down to 4 K, and its momentumresolved spectral function resembles electrondoped opencore 4f density functional calculations. The band nodal points of Ce_{3}Pd_{3}Bi_{4} at 4 K are protected by the glidingmirror symmetry and form ringlike structure. Therefore, the Ce_{3}Pt_{3}Bi_{4} compound is topologically trivial Kondo insulator while the Ce_{3}Pd_{3}Bi_{4} compound is a topological nodalline semimetal. 
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