Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Y43: MultiPolar, MultiChannel, and Semimetal Kondo systemsLive

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Sponsoring Units: DCMP Chair: Keshav Shrestha, West Texas State Univ 
Friday, March 19, 2021 11:30AM  11:42AM Live 
Y43.00001: Rise and Fall of NonFermi Liquid Fixed Points in Multipolar Kondo Problems Daniel Schultz, Adarsh S Patri, YongBaek Kim Recently it was shown that the multipolar Kondo problem, wherein a quantum impurity carrying higherrank multipolar moments interacts with conduction electrons, leads to novel nonFermi liquid states. Because of the multipolar character of the local moments, the form of the interaction with conduction electrons is strongly dependent on the orbitalsymmetry of the conduction electrons via crystalline symmetry constraints. This suggests that there may exist a variety of different nonFermi liquid states in generic multipolar Kondo problems depending on the character of conduction electrons. In this work, using renormalization group analysis, we investigate a model where the multipolar local moment is coupled to conduction electrons with two different orbitalsymmetry components. When each orbitalsymmetry component is present alone, nonFermi liquid states with exactly the same thermodynamic singularities appear. When both orbitalsymmetry components are allowed, however, a completely different nonFermi liquid state arises via the quantum fluctuations in the mixed scattering channels. This remarkable result suggests that the multipolar Kondo problem presents novel opportunities for the discovery of unexpected nonFermi liquid states. 
Friday, March 19, 2021 11:42AM  11:54AM Live 
Y43.00002: Critical theory of nonFermi liquid fixed point in multipolar Kondo problem Adarsh S Patri, YongBaek Kim The embedding of multipolar local moments in a metallic host offers a route to uncover novel spinorbital entangled quantum ground states. In this talk, we theoretically investigate the multipolar Kondo problem, where conduction electrons interact with localized higherrank multipolar moments (such as quadrupolar or octupolar moments). Using nonabelian bosonization, current algebra, and conformal field theory approaches, we demonstrate the appearance of a novel nonFermi liquid state, which is characterized by highly singular powerlaw behaviours in its physical properties. This work provides the foundation for the discovery of a variety of nonFermi liquid ground states in quantum materials through the introduction of multipolar moments in itinerant electron systems. 
Friday, March 19, 2021 11:54AM  12:06PM Live 
Y43.00003: NonFermi Liquid Phenomena and Novel Quantum Criticality in the Multipolar Kondo System PrV_{2}Al_{20} Mingxuan Fu, Akito Sakai, Naoki Sogabe, Masaki Tsujimoto, Yosuke Matsumoto, Satoru Nakatsuji One of the central mysteries of strongly correlated electronic systems is the origin of the nonFermi liquid (NFL) phase — a highly entangled quantum state that holds abiding fascination owing to its prime connections with unconventional superconductivity and quantum critically [1]. Metallic systems with strong hybridization between multipolar local moments and conduction electrons offer a fascinating stage for exploring the purely orbitaldriven NFL and quantum criticality. The heavyfermion superconductor PrV_{2}Al_{20 }is a model system of this kind, which features a nonmagnetic groundstate doublet, hosting both electric quadrupoles and magnetic octupoles [2,3]. Here, we present a comprehensive study of the NFL behavior in PrV_{2}Al_{20} single crystals using transport and thermodynamic measurements [3]. Our findings reveal that the multipolar Kondo effect plays a crucial role in shaping the NFL behavior in PrV_{2}Al_{20} and leads to fieldinduced quantum critical phenomena radically different from that observed in magnetic heavy fermion systems. 
Friday, March 19, 2021 12:06PM  12:18PM Live 
Y43.00004: Nonlinear Conductance for the Charge TwoChannel Kondo Model Luiz Guessi, Thomas Barthel, Luiz Nunes Oliveira, Harold U Baranger Motivated by a recent experiment [Z. Iftikhar et al, Nature 526, 233 (2015)], we report a timedependent DensityMatrix RenormalizationGroup computation of the lowtemperature nonequilibrium current across a microscopic metallic island coupled to two independent leads. At low T, the nearly complete freezing of the island degrees of freedom leaves only two degenerate states, whose charges differ by one electron. The dynamics of charge conduction through the island is modeled by an anisotropic twochannel Kondo Hamiltonian, in which the two impurityspin components represent the island states, a spin flip emulating the transfer of one electron to or from the leads. We have computed the current, following the application of a sudden bias eV, over time intervals substantially longer than the characteristic time \hbar/(eV), albeit short on the Kondo time scale. For symmetric couplings, plotted as a function of eV, the differential conductances show universal behavior. For asymmetric couplings, the differential conductances display the expected crossover from Fermiliquid to nonFermiliquid behavior as eV grows. 
Friday, March 19, 2021 12:18PM  12:30PM Live 
Y43.00005: Floquet engineering multichannel Kondo lattices Victor Quito, Rebecca Flint Floquet engineering consists of coupling a system to a periodic potential, typically light, leading to transient phases rare or even impossible to find in equilibrium. We show that the Kondo lattice can be Floquettuned to generate multichannel Kondo physics even when the equilibrium case has a single channel. By changing the driving protocol, we can tune to two and threechannel multicritical points. These emergent channels are differentiated by symmetry, and their strength can be controlled by light polarization, frequency, and amplitude. We first demonstrate our findings in a toy model on the square lattice. Then, we explore a realistic model for J = 5/2 Ce ions in a tetragonal environment, which presents unique features arising from spinorbit coupling. Unpolarized light, constructed by polarization averaging [V. L. Quito and R. Flint, arXiv:2003.04272], can be particularly useful for designing multichannel Kondo lattices that present Floquetinduced Kondo models not found in equilibrium. The multichannel Kondo lattice can give rise to composite pair superconductivity, and we discuss how the nature of the superconductivity can be tuned, with application to the 115 materials. 
Friday, March 19, 2021 12:30PM  12:42PM Live 
Y43.00006: Mobile Majorana zeromodes in twochannel Kondo lattices Milan Kornjaca, Victor Quito, Rebecca Flint Nonabelian anyons are highly desired for topological quantum computation purposes, with Majorana fermions a promising possibility, particularly localized zero modes with nontrivial mutual statistics. Yet realizing Majorana zero modes in matter is a challenge, with proposals in fractional quantum hall states, chiral superconductors and spin liquids, but no clear successes. Heavy fermion materials have long been known to host Majoranas at twochannel Kondo impurities, however, these impurities are difficult to manipulate, and moreover occur in metals, where Majoranas at different impurities can communicate and lose their topological nature. Here, we show that topological defects in a lattice of these twochannel Kondo impurities can also host Majoranas, but can be engineered to avoid the above difficulties, providing the novel possibility of nontrivial, stable and manipulable Majorana zero modes in a twochannel Kondo insulator. We examine this effect in a simple square octagon model at quarter filling with an antiferrohastatic order that opens up a hybridization gap at the quadratic band touching point and show that skyrmionic defects in this state host Majorana zero modes. 
Friday, March 19, 2021 12:42PM  12:54PM Live 
Y43.00007: High harmonic generation in WeylKondo semimetals Sarah Grefe, Rohit P Prasankumar, Qimiao Si, JianXin Zhu When highintensity light interacts with solid state materials, nonlinear processes generate higherorder harmonics of the incident light. In the presence of strong correlations, high harmonic generation (HHG) characterizes manybody properties such as coherent excitations & charge dynamics, whereas in topological matter, nontrivial Berry curvature contributes to second harmonic generation (SHG) through interband transitions. In light of the discovery of strongcorrelationdriven topology in both experimental^{13} & theoretical^{46} studies of a WeylKondo semimetal (WKSM), we study the HHG of the WKSM. Using a Peierlssubstituted noncentrosymmetric periodic Anderson model including spin orbit coupling, we elucidate the effect of strong correlations on the SHG order and its intensity. 
Friday, March 19, 2021 12:54PM  1:06PM Live 
Y43.00008: Quantum Criticality and Sequential Destruction of SpinOrbitalcoupled Kondo Effect* Silke Paschen, ChiaChuan Liu, Ang Cai, Rong Yu, Emilian Nica, Qimiao Si Quantum critical points (QCPs) and the beyondLandau physics of Kondo destruction [1,2] are being studied in systems with multipolar degrees of freedom. The compound Ce_{3}Pd_{20}Si_{6 }shows evidence for two consecutive Fermi surface collapsing QCPs as it is tuned from a paramagnetic to an antiferroquadrupolar and then to an antiferromagnetic state [3]. A theory was advanced [3] for a sequential destruction of spinorbitalcoupled Kondo effect in an SU(4) BoseFermi Kondo model, an effective model for a multipolar Kondo lattice. Here we report an analytical renormalization group calculation of the model with Ising anisotropy. We show that a generic trajectory in the parameter space contains two QCPs associated with the destruction of the orbital and spin Kondo effects, respectively. Our work establishes a firm theoretical ground for the notion of sequential Kondo destruction. Implications for metallic quantum criticality in general are discussed. 
Friday, March 19, 2021 1:06PM  1:18PM Live 
Y43.00009: Quantum Criticality of Kondo Lattice Model: A Renormalization Group Study via Quantum nonLinear Sigma Model* Yiming Wang, ChiaChuan Liu, Qimiao Si Quantum criticality has been an active research topic in condensed matter physics, with major efforts being devoted to the heavy fermion metals [1]. From a theoretical perspective, the interplay between different kinds of degrees of freedom makes it challenging to develop a unified framework to study the quantum criticality. Here we approach the problem from the magnetically ordered side, and represent the Kondo lattice model using a quantum nonlinear sigma model with an additional coupling to itinerant fermions. By treating the renormalization of the bosonic and fermionic degrees of freedom on an equal footing, we analyze the effect of the Kondo coupling on the quantum criticality. Our results shed new light on the global phase diagram of the heavy fermion systems [2] and, especially, the behavior of frustrated Kondo lattice [3,4]. 
Friday, March 19, 2021 1:18PM  1:30PM Live 
Y43.00010: Strange metal state in a paramagnetic heavyfermion Kondo lattice: Dynamical largeN fermionic multichannel approach Jiangfan Wang, YungYeh Chang, ChungHou Chung The mechanism of strange metal (SM) with unconventional charge transport near magnetic phase transitions has become an outstanding open problem in correlated electron systems. Recently, an exotic quantum critical SM phase was observed in paramagnetic frustrated heavyfermion materials near Kondo breakdown (KB). We establish a controlled theoretical framework to this issue via a dynamical largeN fermionic multichannel ap proach to the twodimensional KondoHeisenberg lattice model, where KB transition separates a heavyFermi liquid from fermionic spinliquid state. With Kondo fluctuations being fully considered, we find a distinct SM behavior with quasilinearintemperature scattering rate associated with KB. When particlehole symmetry is present, signatures of a critical spinliquid SM phase as T → 0 are revealed with ω/T scaling extended to a wide range. We attribute these features to the interplay of critical bosonic charge (Kondo) fluctuations and gapless fermionic spinons. The implications of our results for the experiments are discussed. Please refer to arXiv :2005.03427. 
Friday, March 19, 2021 1:30PM  1:42PM Live 
Y43.00011: New variational method for quantum impurity problems Samuel Boutin, Bela Bauer Quantum impurity models  systems of a few strongly interacting degrees of freedom coupled to a large bath of noninteracting fermions  constitute an important class of problems in condensed matter physics. Despite the small number of interacting modes involved, this class of problems can exhibit rich manybody physics phenomena. Motivated by recent formal results, showing that a coherent superposition of nonorthogonal fermionic Gaussian states is an efficient approximation to the ground states to quantum impurities [Bravyi and Gosset, Comm. Math. Phys., 356 451 (2017)], we present a new practical approach for performing variational calculations for quantum impurity problems. The method uses an approximate projection of imaginarytime equations of motion that decouples the dynamics of each Gaussian state forming the ansatz. As a first application of the method, we calculate properties of the screening cloud of an Anderson impurity and the impurity contribution to the entanglement entropy. We also benchmark our approach using density matrix renormalization group (DMRG) calculations. Finally, we present ongoing work on the study of the ground state of the overscreened multichannel Kondo model, a problem difficult to tackle using conventional numerical tools. 
Friday, March 19, 2021 1:42PM  1:54PM Live 
Y43.00012: Kondodriven topological semimetals in two and three dimensions Chandan Setty, Haoyu Hu, Sarah Grefe, Silke Paschen, Jennifer Cano, Qimiao Si In strongly correlated settings, how space group symmetry influences electronic 
Friday, March 19, 2021 1:54PM  2:06PM Live 
Y43.00013: WeylKondo semimetal: Topological quantum phase transition by a Zeeman coupling Sarah Grefe, HsinHua Lai, Silke BuehlerPaschen, Qimiao Si Recently a WeylKondo semimetal (WKSM) has been concurrently discovered in theoretical^{1,2} and experimental^{3,4} studies. In the solutions to the Anderson lattice model with a nonsymmorphic, noncentrosymmetric crystalline lattice, in the presence of spinorbit coupling, the Kondo effect cooperates with the spacegroup symmetry to drive the Weyl nodes and pin them at the Fermi energy. Intriguingly, recent experiments have uncovered how the magnetic field quenches the WKSM.^{5} Here, we studied the Anderson lattice model with a broken time reversal symmetry, via a Zeeman coupling.^{6} Tuning the Zeeman coupling controls the position and number of Weyl nodes and leads to the eventual annihilation of the nodes before the Kondo energy scale vanishes. Our results provide a microscopic understanding of the highfield experiments on the WKSM. 
Friday, March 19, 2021 2:06PM  2:18PM Live 
Y43.00014: Bosonization and Refermionization of Multichannel Kondo Hamiltonians Aleksandar Ljepoja, Nayana Shah, Carlos J Bolech Multichannel Kondo Hamiltonians are of interest in a wide variety of problems and have been studied using a range of techniques. Here we are interested in employing bosonization methods for these Hamiltonians. Building on the recently developed consistent framework [1,2], and using old and new guidelines for bosonizationdebosonization procedure for theories with boundary degrees of freedom, we gain new insights about the refermionization of these Hamiltonians. We analyze and evaluate these using Greenfunction based calculations, both in and out of equilibrium. 
Friday, March 19, 2021 2:18PM  2:30PM Live 
Y43.00015: Strong correlation effects on the nonlinear response in WeylKondo semimetals Akira Kofuji, Yoshihiro Michishita, Robert Peters Recently it has become clear that a nonlinear Hall effect(NLH) can emerge even in a timereversal symmetric system, which is closely connected with the topological nature of the material, namely the “Berry curvature dipole”[1]. This characteristic makes the NLH an alternative to studying the topology of the material, even when it is difficult to determine the band structure directly, e.g., in strongly correlated topological materials. 
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