Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session W63: Kondo PhysicsRecordings Available
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Sponsoring Units: DCMP Chair: Matthew Enjalran, Southern Conn State Univ Room: Hyatt Regency Hotel -Grant Park A |
Thursday, March 17, 2022 3:00PM - 3:12PM |
W63.00001: Fractionalization and Symmetry Breaking in Multichannel Kondo Lattices Yang Ge, Yashar Komijani Multichannel Kondo lattices describe the interaction between a lattice of local moments and multi-channel conduction bands and are used to model the rich physics that appears in heavy-fermion quantum materials. Previous studies indicate that the channel symmetry in these systems is spontaneously broken at low temperatures. Various patterns of channel-symmetry breaking can generate entanglement potentially useful for quantum information. Here, we use dynamical large-N method with a Schwinger boson representation of spins to go beyond both mean-field approximation and the independent-bath approximation mostly employed in previous works. This allows us to capture electronic dissipation and explore different regimes of screening in arbitrary lattices that reveal a spontaneous channel symmetry breaking under multichannel Kondo interaction. By going from one to infinite dimension we observe that channel asymmetry changes from being an irrelevant perturbation to a relevant one in the renormalization group sense. Additionally, in contrast to the perfectly screened 1D Kondo lattice, the over-screened Kondo case is gapless and the channel excitations are fractionalized into well-defined quasi-particle modes of fermionic holons. The full dispersion of low energy spinon and holon modes given by our numerics enables an effective theory and an analytical solution for the two-channel Kondo lattice in 1D to capture the physics in this critical phase. |
Thursday, March 17, 2022 3:12PM - 3:24PM |
W63.00002: Algebraic Hastatic Order in One-Dimensional Two-Channel Kondo Lattice Milan Kornjaca, Rebecca Flint We study the one-dimensional two-channel Kondo lattice model using density matrix renormalization group method. Extending the earlier work (Schauerte et. al., PRL 94:147201, 2005), we show that algebraic hastatic density wave order appears generically for strong coupling, leading to a rich phase diagram fundamentally different from the one-dimensional single-channel Kondo lattice. The hastatic phases are metallic away from quarter filling and we show that they correspond to different heavy Tomonaga-Luttinger liquids with Fermi surface wave-vectors unrelated to light or heavy wave-vectors in the single-channel Kondo case. Numerical results are compared with large-N mean-field predictions and an additional vectorial order parameter associated with hastatic order is detected which we ascribe to the unique spinorial nature of the order. |
Thursday, March 17, 2022 3:24PM - 3:36PM |
W63.00003: Multi-flavor topological Kondo effect Guangjie Li, Yuval Oreg, Jukka Vayrynen The topological Kondo model does not have a perturbative intermediate fixed point when the lead fermions are weakly interacting. We introduce a modified physically motivated Hamiltonian by adding Ν flavors to the topological Kondo model. We calculate the perturbative renormalization group equations and consider the large-Ν limit of the β functions. In the isotropic limit, we find an intermediate stable fixed point, which can be brought to weak coupling in the large-N limit. We investigate the effects of weak anisotropy and the stability of the strong coupling fixed point to complete the flow diagram for the coupling constants. We calculate the temperature- and voltage-dependence of the conductance matrix to obtain experimentally observable signatures of our results. |
Thursday, March 17, 2022 3:36PM - 3:48PM |
W63.00004: Charge-Spin-Flavor separation in quantum impurity problems Aleksandar Ljepoja, C. J Bolech, Nayana Shah The Kondo problem is an ideal example of spin-charge separation at all energies. In multichannel versions of the problem, an additional internal degree of freedom, sometimes called flavor, labels the different channels and (partially) gets decoupled as well. Following a critical revision of the procedures for bosonization and debosonization of quantum impurity models [1,2], we study the spin-flavor interplay in detail by comparing refermionized versions of the model done following different schemes. We find that non-equilibrium probes can be more sensitive to the spin-flavor interplay at the strong-coupling fixed point as compared to thermodynamic measurements. |
Thursday, March 17, 2022 3:48PM - 4:00PM |
W63.00005: The Anderson impurity problem in a uniform fractal host Angkun Wu, Daniel Bauernfeind, Xiaodong Cao, Andrew J Millis, Sarang Gopalakrishnan, Kevin Ingersent, Jed Pixley We report our solution of the Anderson model for a magnetic impurity weakly hybridizing with host electrons whose density of states (DOS) is described by a symmetric uniform Cantor set. This fractal DOS naturally lends itself to a logarithmic binning of the band energy. Discretized in this way, the original problem can be mapped onto Anderson Hamiltonian on a Wilson tight-binding chain with exponentially decaying nearest-neighbor hoppings. The resulting problem is entirely equivalent to one arising in the numerical renormalization-group (NRG) treatment of the Anderson model with a smooth (non-fractal) band diverging in a power-law fashion at the Fermi energy, in which the system will always flow toward a strong-coupling regime and the impurity makes negative contributions to the magnetic susceptibility and the entropy. Decreasing the width of the logarithmic energy bins in a series of steps to approach the original continuum limit of the problem resolves more structures in the fractal and manifests periodicity in scaled hoppings on the Wilson chain. Full NRG calculations confirm that all members of this series of discretizations describe the same asymptotic divergence of the DOS, described by a power connected to the fractal dimension of the uniform Cantor set. |
Thursday, March 17, 2022 4:00PM - 4:12PM |
W63.00006: The Anderson impurity problem in a multifractal host Angkun Wu, Daniel Bauernfeind, Xiaodong Cao, Andrew J Millis, Sarang Gopalakrishnan, Kevin Ingersent, Jed Pixley We present results of a numerical study of the single-impurity Anderson problem in a one-dimensional quasicrystal described by the Aubry-Andre (AA) model. The AA model exhibits an Anderson localization transition at a critical value of the incommensurate potential strength. At the critical point, the impurity hybridizes with the electrons through the local density of states (LDOS) based on the fractal spectrum (a non-uniform Cantor set) and multifractal wavefunctions. The complexity of the resulting Anderson impurity problem can be attributed to the multi-scaling from the multifractal LDOS over different ranges of energy and temperature. For these systems lacking translation symmetry, we combine the kernel polynomial method (KPM) with the numerical renormalization group (NRG) to efficiently obtain the parameters of the tight-binding Wilson chain without the need for any integration. We benchmark this KPM+NRG approach against the density matrix renormalization group in their regime of mutual applicability. We present and interpret low-temperature thermodynamic properties. |
Thursday, March 17, 2022 4:12PM - 4:24PM |
W63.00007: Charge-Kondo circuits as quantum simulators Andrew K Mitchell, David Goldhaber-Gordon, Winston Pouse, Frederic Pierre Quantum nanoelectronic circuits, comprising charge-Kondo quantum dot components, offer a uniquely versatile and exquisitely controllable route to analog quantum simulation of complex models. In this work, we study the simplest one- and two-site systems, comparing experiment and theory to validate the models realized by such circuits. |
Thursday, March 17, 2022 4:24PM - 4:36PM Withdrawn |
W63.00008: Automatic generation of Hamiltonians describing spins in a bath from a wide range of interacting systems Benedikt M Schoenauer We describe an automated algebraic Schrieffer-Wolff approach that yields a description of complex systems, in which the interactions between spin-like orbitals and designated bath-orbitals no longer involve any particle transfer, such that a representation of the spin-like orbitals by means of simple spin degrees of freedom becomes feasible. |
Thursday, March 17, 2022 4:36PM - 4:48PM |
W63.00009: Non-Trivial Fixed Points and Truncated SU(4) Kondo Models in a Quasi-Quartet Multipolar Quantum Impurity Problem Daniel J Schultz, Adarsh S Patri, Yong Baek Kim The multipolar Kondo problem has seen recent theoretical and experimental interest due to proposals of novel non-Fermi liquid states and the availability of a variety of material platforms. The multipolar nature of local moments, in conjunction with constraining crystal field symmetries, leads to numerous possible interactions and resulting non-Fermi liquid ground states. In this work, inspired by recent experiments on the tetragonal material YbRu2Ge2, which has been shown to exhibit a local moment with a quasi-fourfold degenerate ground state, we consider the Kondo effect for such a quasi-quartet multipolar impurity. In the tetragonal crystal field environment, the local moment supports dipolar, quadrupolar, and octupolar moments. Using renormalization group analysis, we uncover a number of quantum ground states characterized by non-trivial fixed points. It is shown that these fixed points are described by truncated SU(4) Kondo models, where only some of the SU(4) generators (representing the impurity degrees of freedom) are coupled to conduction electrons. Such novel non-trivial fixed points are unique to the quasi-quartet multipolar impurity. |
Thursday, March 17, 2022 4:48PM - 5:00PM |
W63.00010: Nonlinear response induced by Ferromagnetism in a Noncentrosymmetric Kondo Lattice system Koki Shinada, Robert Peters Recently, nonlinear response has been actively studied in noncetrosymmeric systems. Previous studies has focused on noninteracting systems and showed a second order conductivity reflects on the inversion breaking structures or topological nature. On the other hand, strongly correlated system is also interesting platform. S. Dzsaber et.al. [1] have experimentally observed a giant nonlinear Hall response in a Kondo system Ce3Bi4Pd3. This hugeness of the nonlinear conductivity is explained theoretically by the renormalization effect [2]. |
Thursday, March 17, 2022 5:00PM - 5:12PM |
W63.00011: Interplay of Majorana and Kondo physics in a spin-charge entangled double quantum dot Ireneusz Weymann, Piotr Majek The signatures of Majorana zero-energy mode leaking into a spin-charge entangled double quantum dot |
Thursday, March 17, 2022 5:12PM - 5:24PM |
W63.00012: Dynamics of a Moving Kondo Impurity in the Spin Chain Runze Chi, Tao Xiang, Mingpu Qin, Haijun Liao The problem of a single impurity interacting with a bath has been considered in various systems. Here we consider the single hole limit of a one-dimensional two-band model, which is relevant to the physics of cuprates. Combining Galilean transformation and density matrix renormalization group (DMRG) method, we obtain not only the ground state properties but also the low-energy dispersion. It is shown that, with an increasing Kondo coupling JK, the total momentum of the ground state has a crossover from 0 to π/2, which corresponds to the t-J physics in the large JK limit. Simultaneously, the spin of the hole will be screened with antiferromagnetic coupling JK. This method can be easily applied to other single-impurity problems in one dimension and ladder systems, which opens the door to study the dynamics of a single particle coupled to a bath. |
Thursday, March 17, 2022 5:24PM - 5:36PM |
W63.00013: Revisiting a Classic Kondo-System: Co/Cu(111) Felix Friedrich, Robin Boshuis, Artem Odobesko, Matthias Bode Single cobalt atoms on the (111) surfaces of noble metals were long time considered prototypical systems of the Kondo effect in STM experiments [1]. Spectroscopic measurements on these atoms reveal a Fano-like dip around the Fermi-level, which was explained by two interfering tunneling paths of electrons, one directly into the surface and the second one into a Kondo resonance. However, Bouaziz et al. [2] recently proposed that the observed feature actually originates from spin-flip excitations of the Co atom spin induced by the tunneling electrons. Further, interaction between these spin-flip excitations and conduction electrons was predicted to lead to the formation of a new quasiparticle, called spinaron. |
Thursday, March 17, 2022 5:36PM - 5:48PM |
W63.00014: Extracting fractional entropy of exotic quasiparticles from conductance measurements Cheolhee Han, Andrew K Mitchell, Zubair Iftikhar, Yaakov Kleeorin, Anne Anthore, Frédéric Pierre, Yigal Meir, Eran Sela Fractional entropy is a signature of nonlocal degrees of freedom, such as Majorana zero modes or more exotic non-Abelian anyons. However, in the mesoscopic quantum systems hosting these states direct entropy measurements remain highly challenging. One promising approach utilizes Maxwell relations to extract entropy changes from charge measurements. In this talk, applying this approach to a metallic quantum dot system, we propose a feasible way to detect the fractional entropy in the two- and three-channel Kondo effects, corresponding to Majorana and Fibonacci zero modes, respectively, by measuring the charge occupation of the dot. Furthermore, we analyze the relation between the charge occupation and the conductance, which is already measured. The entropy extracted from the experimental data strongly supports the feasility of the proposed experiment. Our protocol provides a general route towards a direct extraction of entropy from charge measurements in mesoscopic systems. |
Thursday, March 17, 2022 5:48PM - 6:00PM |
W63.00015: Universal entanglement of the multi-channel Kondo effects Donghoon Kim, Jeongmin Shim, H.-S. Sim An essential concept of the impurity problem is the quantum coherent screening of the impurity. In this work, we develop a method to compute the entanglement negativity between the impurity and its environment in spin-1/2 impurity problems, based on the boundary conformal field theory. We apply our method to the multichannel Kondo model, a strongly correlated system in which conduction electrons of multiple channels compete to screen one impurity, to unveil quantum coherence inside the Kondo screening length. We show that the entanglement has the maximal value independent of the number of the screening channels at zero temperature. At low temperature, we show that the entanglement exhibits a power-law thermal decay with a fractional number exponent, and it is attributed to the boundary conformal primary field representing the impurity. These results are confirmed by the numerical renormalization group. We quantify the spatial distribution of the Kondo screening cloud through the entanglement. Using the quantification, we suggest how to detect the multichannel Kondo cloud in a quantum dot device. |
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