Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S46: Strong Electronic Correlations in Topological MaterialsLive

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Sponsoring Units: DCMP Chair: Thais Victa Trevisan, Ames Lab 
Thursday, March 18, 2021 11:30AM  11:42AM Live 
S46.00001: Fragile topology and flatband superconductivity in the strongcoupling regime Valerio Peri, Zhida Song, Andrei B Bernevig, Sebastian Huber Recent theoretical works unveiled that crystalline symmetries can stabilize topologically fragile Bloch bands that challenge our very notion of topology: one can trivialize these bands through the addition of trivial Bloch bands. Here, we show via auxiliaryfield Monte Carlo simulations how fragile topology enhances the superfluid weight and hence the superconducting critical temperature. This feature is particularly relevant in flatband systems where the conventional contribution to the superfluid weight vanishes and might explain the high transition temperature observed in magicangle twisted bilayer graphene. 
Thursday, March 18, 2021 11:42AM  11:54AM Live 
S46.00002: Electrostatic Interactions and Band Topology in Graphene Stacks Pierre Anthony Pantaleon Superconducting and insulating phases are wellestablished in twisted graphene bilayers, and they have also been reported in other arrangements of graphene layers. We investigate three such situations, (untwisted) bilayer graphene on hBN, two graphene bilayers twisted with respect to each other, and a single ABC stacked graphene trilayer on hBN. In all these cases, narrow bands emerge. The resulting high density of states enhances the role of interactions. We study the band topology effects and the longrange electronelectron interaction on these narrow bands. A self consistent electrostatic potential does not modify significantly the shape and width of the bands in the three cases considered here, in contrast to the effect that such a potential has in twisted bilayer graphene. 
Thursday, March 18, 2021 11:54AM  12:06PM Live 
S46.00003: Currentinduced reversal of anomalous Hall conductance in twisted bilayer graphene Ying Su, ShiZeng Lin Twisted bilayer graphene signatured by the flat band and strong electronic interaction at the magic angle has sparked great interests. One of the fascinating experimental observations in twisted bilayer graphene is the emergent quantum anomalous Hall effect at 3/4 filling and the sign of Hall conductance can be flipped by a dc current. The experiment implies a switching of the valley polarization and topology in twisted bilayer graphene. Here we present a theory on the currentinduced switching of valley polarization and topology. The presence of current in the bulk causes the redistribution of electron occupation in bands near the Fermi energy, which then deforms and shifts the band dispersion due to the Coulomb interaction. Above a critical current, the original occupied and empty bands can be swapped resulting in the switching of valley polarization and topology in twisted bilayer graphene. 
Thursday, March 18, 2021 12:06PM  12:18PM Live 
S46.00004: Exact and perturbative insulator states and excitations in twisted bilayer graphene Biao Lian, Zhida Song, Nicolas Regnault, Aditya Cowsik, Fang Xie, Dmitri K. Efetov, Ali Yazdani, Andrei B Bernevig We study the low energy states of the flatband projected Hamiltonian of magic angle twisted bilayer graphene with Coulomb interactions. By treating the nonchiral interaction and the kinetic energy as perturbations, we analytically derive the exact or perturbative strongly interacting (Chern) insulator ground states at all integer fillings \nu<4. We find the ground state has Chern number mod(\nu,2), and is intervalley coherent (valley polarized) at fillings \nu=0,1,2 (\nu=3). We further show that the insulators have analytically computable charge 0, +1,+2 excitations. We show that the Goldstone modes of the ground states are quadratic. Furthermore, from the charge 1 and 2 excitations, we prove the absence of Cooper pairing from the Coulomb interaction in the flat band limit, which suggests other superconductivity mechanisms. 
Thursday, March 18, 2021 12:18PM  12:30PM Live 
S46.00005: Interactioninduced topological phase transition and Majorana edge states in lowdimensional orbitalselective Mott insulators Jacek Herbrych, Maksymilian Sroda, Gonzalo Alvarez, Marcin Mierzejewski, Elbio Dagotto It is known that superconductivity induced on a topological insulator's surface can lead to exotic Majorana modes. In this context, ironbased high critical temperature superconductors are among the main candidates to host such exotic phenomenon. Moreover, it is commonly believed that the Coulomb interaction is vital for the magnetic and superconducting properties of these systems. This work bridges these two perspectives and shows that the Coulomb interaction can also drive a trivial superconductor with orbital degrees of freedom into the topological phase. Namely, we show that above some critical value of the Hubbard interaction, identified by the change in entropy behaviour, the system simultaneously develops spiral spin order, a highly unusual triplet amplitude in superconductivity, and, remarkably, Majorana fermions at the edges of the system. 
Thursday, March 18, 2021 12:30PM  12:42PM Live 
S46.00006: Topologically protected, correlated end spin formation in carbon nanotubes Gergely Zarand, Catalin Pascu Moca, Balazs Dora, Örs Legeza, Wataru Izumida For most chiralities, semiconducting carbon nanotubes display topologically protected end states of multiple degeneracies. In the presence of interactions, these midgap states act as naturally formed quantum dots, halffilled for generic, neutral nanotubes. We demonstrate using density matrix renormalization group based quantum chemistry tools that the presence of Coulomb interactions induces the formation of massive end spins [C.P. Moca et al, Phys. Rev. Lett. 125, 056401 (2020)]. In the limit of infinite nanotube radius, these end spins transform into ferromagnetic graphene nanoribbon edge states. The interaction between the two ends is sensitive to the length of the nanotube, its dielectric constant, as well as the size of the spins: for S=1/2 end spins their interaction is antiferromagnetic, while for S>1/2 it changes from antiferromagnetic to ferromagnetic with increasing nanotube length. Controlling the exchange interaction by changing the dielectric constant of the environment provides a possible platform for twospin quantum manipulations. 
Thursday, March 18, 2021 12:42PM  12:54PM Live 
S46.00007: Strong correlation effect in DFTbased topological characterization of WeylKondo semimetals Jamin Kidd, Ruiqi Zhang, Jianwei Sun It is commonly accepted that density functional theory (DFT) inaccurately describes materials for which the strong correlation effect (SCE), characterized by a strong interelectronic Hubbard U, is prominent. This is typically the case for d and felectron systems. However, recent advances in DFT development at the metaGGA (metageneralized gradient approximation) level have demonstrated significantly improved descriptions of the electronic and magnetic properties of highT_{C} cuprate superconductors without explicitly involving U.^{1} Naturally, one asks whether such improvements are present for other types of correlated materials and other material properties. In this work, we use DFT to study the electronic and topological properties of the recently proposed WeylKondo semimetal (WKSM) Ce_{3}Pd_{3}Bi_{4}.^{2} We model the system with and without valence felectrons to identify the role that the SCE plays when determining bulk band topology. Additionally, we consider different density functionals and discuss the remaining obstacles in achieving accurate firstprinciples characterization of interacting topological materials. 
Thursday, March 18, 2021 12:54PM  1:06PM Live 
S46.00008: STM study of many body zeroenergy resonance in kagome Weyl antiferromagnet Mn_{3}Sn Songtian Sonia Zhang, Jiaxin Yin, Muhammad Ikhlas, Nana Shumiya, Guoqing Chang, Rui Wang, Stepan Tsirkin, Titus Neupert, Satoru Nakatsuji, Zahid Hasan We use scanning tunneling microscopy to elucidate the atomically resolved electronic structure in the strongly correlated kagome Weyl antiferromagnet Mn_{3}Sn. In stark contrast to its broad singleparticle electronic structure, we observe a pronounced resonance with a Fano line shape at the Fermi level resembling the manybody Kondo resonance. We find that this resonance does not arise from the step edges or atomic impurities but the intrinsic kagome lattice. Moreover, the resonance is robust against the perturbation of a vector magnetic field, but broadens substantially with increasing temperature, signaling strongly interacting physics. We show that this resonance can be understood as the result of geometrical frustration and strong correlation based on the kagome lattice Hubbard model. Our results point to the emergent manybody resonance behavior in a topological kagome magnet. 
Thursday, March 18, 2021 1:06PM  1:18PM Not Participating 
S46.00009: Colossal anomalous Nernst effect in a correlated noncentrosymmetric kagome ferromagnet Tomoya Asaba, Vsevolod Ivanov, Sean Thomas, Sergey Savrasov, Joe Thompson, Eric D Bauer, Filip Ronning Analogous to the Hall effect, the Nernst effect is the generation of a transverse voltage due 
Thursday, March 18, 2021 1:18PM  1:30PM Live 
S46.00010: Towards a Topological Quantum Chemistry description of strongly correlated systems: the case of the Hubbard diamond chain Mikel Iraola Iñurrieta, Niclas Heinsdorf, Dominik Lessnich, Thomas Mertz, Apoorv Tiwari, Francesco Ferrari, Stephen Winter, Mark Fischer, Frank Pollmann, Titus Neupert, Roser Valenti, Maia Garcia Vergniory The recently introduced Topological Quantum Chemistry (TQC) formalism provides a description of the universal global properties of all possible atomic limit band structures in all groups, in real and momentum space. Using TQC, an algorithm interfaced with ab initio codes was developed, which allowed for highthroughput calculations on material databases identifying thousands of materials displaying topological properties at the Fermi level. However, it is an open question to which extent this formalism can be generalized to correlated systems that can exhibit symmetry protected topological phases which are not adiabatically connected to any band insulator. We address this question by considering the Hubbard diamond chain and apply TQC, together with the concept of topological Hamiltonian and Cluster Perturbation Theory, to study the different topological phases that this system exhibits and the phase transitions between them. We will compare our results with more sophisticated numerical methods. 
Thursday, March 18, 2021 1:30PM  1:42PM Live 
S46.00011: Symmetry protected invariants for the singleparticle Green’s function of interacting topological insulators Dominik Lessnich, Stephen Winter, Roser Valenti The formalisms of topological quantum chemistry (TQC) [Bradlyn et al., Nature 547, 298 (2017)] and symmetry indicators [Po et al., Nature Communications 8, 50 (2017)] can be used to identify nontrivial topology protected by spatial symmetries in noninteracting lattice systems in all 230 space groups. 
Thursday, March 18, 2021 1:42PM  1:54PM 
S46.00012: CoulombEngineered Topology Malte Roesner, Jose Lado The interplay of topology and interactions is at the heart of current condensed matter research. In particular, intensive efforts are being directed towards engineering artificial systems displaying topological excitations. Most of these efforts focus on singleparticle properties neglecting possible engineering routes via the modifications to the fundamental manybody interactions. Here [1] we propose a simple platform in which topologically nontrivial manybody states emerge solely from dielectricallyengineered Coulomb interactions in an otherwise topologically trivial singleparticle band structure. We demonstrate how our proposal can be realized in onedimensional systems, such as quantumdot chains, by exploiting Coulomb engineering, which has recently been applied to a variety of twodimensional materials. Our results put forward Coulomb engineering as a powerful tool to create topological states of matter, with potential applications in a variety of solidstate platforms. 
Thursday, March 18, 2021 1:54PM  2:06PM Live 
S46.00013: Dynamics properties of topological Kondo insultators Marvin Lenk, Johann Kroha Topological Kondo insulators (TKIs) are a new class of topological insulators, emerging through the interplay of strong correlations and spinorbit coupling. In TKIs, the bulk is a narrow band insulator due to the appearance of a localized Kondo resonance near the Fermi level and its hybridization with the conduction band. Additionally, the strong spinorbit coupling of the localized moments generates a nonlocal hybridization between the local moments and the conduction band, which results in a topologically nontrivial band structure and gapless surface states. In the past, TKIs have been described predominantly by slaveboson meanfield (SBMF) calculations. Such static methods are unable to capture finite lifetime effects of the heavy Kondo quasiparticles. It is therefore not possible to investigate physics at the boundaries, like the dynamical emergence of topological edge states, where SBMF calculations become uncontrolled. We design a spinorbit 
Thursday, March 18, 2021 2:06PM  2:18PM 
S46.00014: Time reversal and lattice symmetry breaking in Nd2Ir2O7 observed by Raman scattering. Yuanyuan Xu, Jeremie Teyssier, Takumi Ohtsuki, Satoru Nakatsuji, Dirk Van Der Marel, Natalia Drichko Abstract body: Nd2Ir2O7 is a semimetal compound, in which a competition between spinorbit coupling and electronic correlations may lead to exotic physics. In particular, a Weyl semimetal state was suggested for this material. Using polarized Raman scattering to study this material, we can distinguish between magnetic excitations and transitions over the electronic gap in the insulating regime below 30 K. We follow the evolution of these features on. This allows us to identify two temperature regimes, between 30 and approximately 15 K where we observe an electronic gap and developing of magnetic order related to iridium spins, and the lower temperature regime where we observe evidence of broken symmetry of the lattice. 
Thursday, March 18, 2021 2:18PM  2:30PM Live 
S46.00015: Topological semimetallic and thermoelectric properties of layered AMSb materials Dinesh Yadav, Gopi Kaphle, Durga Paudyal Present study is focused on the novel semimetallic quantum properties by substituting the 3delements on Msites of AMSb (A=Cs, Rb; M=Zn, Cd). Znbased parent materials are semiconductors, while Cdbased are semimetallic under the influence of spinorbit coupling. By analyzing the band structure, we discover interesting features such as Weyl semimetal, Dirac topology, and halfmetallicity. Using the Boltzmann transport theory, we studied thermoelectric properties of antimonybased nonmagnetic CsZnSb and RbZnSb compounds and found a very good figure of merit (ZT) of 1.05 and 0.90 at 1100 K, respectively. On the other hand, CsCdSb and RbCdSb showed lower ZT values. These layered compounds show high Seebeck coefficients and low thermal conductivities, confirming their potential for high thermoelectric performance. Thus, these materials are promising candidates for semimetallic and thermoelectric phenomena, which are useful for spintronic devices, quantum computing, and highefficiency electronic devices. 
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