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 P43: Heavy Fermions and Kondo InteractionsLive
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Sponsoring Units: DCMP Chair: Kathrin Goetze, Univ of Warwick |
Wednesday, March 17, 2021 3:00PM - 3:12PM Live |
P43.00001: Luttinger count and spin fractionalization in SU(N) invariant Kondo Hamiltonians Tamaghna Hazra, Piers Coleman A characteristic feature of Kondo systems at low temperature is the change of the Fermi surface from a small volume accounting for the filling of the conduction electrons to a large volume that includes the density of the localised spins. This is understood as a fractionalization of the spin degrees of freedom into fermions which then enter the Fermi sea. A non-perturbative proof of the Luttinger count for the SU(2) Kondo lattice model was provided by Oshikawa [1]. We extend Oshikawa's theorem to SU(N) invariant Kondo Hamiltonians. By extending the theorem to arbitrary N, we are able to show that the mechanism of Fermi surface expansion seen in the large N mean-field theory is directly linked to the expansion of the Fermi surface in a spin-1/2 Kondo lattice. We also consider the validity of Luttinger's theorem in the U(1) spin liquid when exchange interactions between the localized spins are included. |
Wednesday, March 17, 2021 3:12PM - 3:24PM Live |
P43.00002: Critical destruction of the Kondo effect in a particle-hole asymmetric Bose-Fermi Anderson model Ananth Kandala, Haoyu Hu, Qimiao Si, Kevin Ingersent Bose-Fermi Kondo/Anderson models are effective Hamiltonians to describe the quantum criticality of strongly correlated metals, especially the beyond-Landau quantum criticality in heavy fermion metals [1]. We revisit the particle-hole asymmetric Bose-Fermi Anderson model with a power-law bosonic bath having a sub-ohmic exponent s < 1 and a power-law fermionic bath having a pseudogap exponent r > 0. Critical destruction of Kondo screening manifests in both the spin and charge channels. Earlier work on the Ising-anisotropic model with r < ½ [2] has identified three ranges of r and s in which the quantum critical behavior is bosonic, fermionic, or of mixed character. Here we present calculations for r > ½ using a quantum Monte Carlo method for both the spin-isotropic and Ising-anisotropic cases, and the numerical renormalization-group method for Ising anisotropy. We advance a consistent description of the quantum critical behavior differing from results recently obtained via an epsilon-expansion approach. Implications for the quantum criticality of Hubbard-like models are discussed. |
Wednesday, March 17, 2021 3:24PM - 3:36PM Live |
P43.00003: Theory of a Strange Metal at the Breakdown of a Heavy Fermi Liquid Erik Aldape, Taylor Cookmeyer, Aavishkar Patel, Ehud Altman We introduce an effective theory for quantum critical points in heavy fermion systems involving a change in carrier density without symmetry breaking. The new theory captures a strong coupling fixed point, leading to robust marginal Fermi liquid transport phenomenology, within a controlled large N limit. This is contrasted with the conventional so-called "slave boson" theory of the Kondo breakdown, where the large N limit describes a weak coupling fixed point and non-trivial transport behavior may only be obtained through uncontrolled 1/N corrections. We compute the weak field Hall coefficient within the effective model as the system is tuned across the transition. We find that between the two plateaus, reflecting the different carrier densities in the two Fermi liquid phases, the Hall coefficient can develop a peak in the critical crossover regime, consistent with recent experimental findings. In the regime of strong damping of emergent bosonic excitations, the critical point also displays a universal "Planckian" transport lifetime, up to weak logarithmic corrections. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P43.00004: The Anderson impurity model in a quasicrystal Angkun Wu, Sarang Gopalakrishnan, Jed Pixley, Kevin Ingersent We will discuss the low energy properties of a single magnetic impurity problem in an electronic quasicrystal. Specifically, the single impurity Anderson model is studied using both the numerical renormalization group (NRG) method and a self-consistent slave particle approach. To simulate large quasicrystal geometries, a hybrid approach is developed that uses the kernel polynomial method (KPM) to obtain the tight-binding coefficients of the Wilson chain without the need to compute the eigenstate spectrum of the host via exact diagonalization or to perform numerical integration. Using this KPM+NRG approach we compute the magnetic susceptibility and impurity spectral function from which we show the Kondo temperature develops a broad distribution in the quasicrystal limit with anomalous averages. The results are compared across quasicrystals in various dimensions. |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P43.00005: Doping the multiorbital Hund's coupled impurity: an exploration of non-Fermi liquid ground states Victor Drouin-Touchette, Elio Koenig, Yashar Komijani, Piers Coleman Motivated by the relevance of Hund’s coupling in Iron-based superconductors, we revisit the problem of a multiorbital Anderson impurity with Hund’s interaction. Using large-N and Schwinger boson techniques, we study the ground state and thermodynamic properties of this system in the mixed valence regime. The physics is characterized by the interplay of Hund’s coupling, which tends to form large moments by aligning the spins of the impurity, and the Kondo effect, which leads to the low-temperature screening of the moments. In the mixed-valence regime, previous NRG studies have found evidence that the system is in proximity to a non-Fermi liquid fixed point. We investigate whether such features survive in the large-N limit. We also explore the possibility that the interplay of the non-integer occupation of orbital sites with a significant Hund’s coupling can generate retarded on-site pairing correlations for the conduction electrons. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P43.00006: Interplay of CEF effects and RKKY interaction in Ce- and Yb-based heavy-fermion compounds Gertrud Zwicknagl, Vilen Zevin We calculate the influence of Crystalline Electric Field (CEF) effects on the indirect |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P43.00007: Theoretical study of odd-parity multipole orders in CeCoSi Megumi Yatsushiro, Satoru Hayami Noncentrosymmetric systems have been attracted due to their fascinating phenomena, e.g., magneto-electric effects. We here focus on the electronic-order-driven inversion symmetry breaking in a centrosymmetric system. In this situation, noncentrosymmetric physical phenomena can be controllable through the spontaneous phase transitions. Besides, the odd-parity multipoles like magnetic toroidal dipole can be activated as unconventional electronic order parameters. The centrosymmetric f-electron compound CeCoSi has been recognized as the odd-parity multipole hosting material in its antiferromagnetic and nonmagnetic phases [1-3], although their origin has not been clarified. In the present study, we have investigated potential odd-parity multipole orders in CeCoSi and its physical phenomena including magneto-current and current-distortion effects [4]. Furthermore, we propose how to detect odd-parity multipoles through NQR/NMR measurement. |
Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P43.00008: THz Spectroscopy of Mixed-Valence YbAl3 Thin Films David Barbalas, Shouvik Chatterjee, Kyle Shen, Darrell Schlom, Peter Armitage Due to interaction of local moment physics and mixed-valence behavior in Yb compounds, Yb heavy fermion compounds have not demonstrated the same range of phenomena seen in other f-orbital materials. Up to this point it has been difficult to measure the low energy electrodynamic response. However, high quality films of YbAl3 have been successfully grown and demonstrate significant changes in the electronic structure of the material mediated by the fluctuating valence. We have investigated the electrodynamic response of the optical conductivit and we discuss the results in the context of prevailing theories. From extended Drude analysis, we identify that YbAl3 scattering rate and effective mass display temperature dependence suggestive of a slow crossover. |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P43.00009: Shubnikov de Haas oscillation measurements on PrT2Cd20 (T = Ni, Pd) “cage” compounds Alexander Breindel, Sheng Ran, Fedor F Balakirev, John Singleton, Hisatomo Harima, M Brian Maple Our group discovered a variation of the RT2X20 (R is a rare earth element, T a transition metal) “1-2-20” compounds with X = Cd. These “cage” compounds contain atomic cages within which R and T ions are located. The localized f- electron states of the R ions hybridize with the ligand states of the surrounding cage ions and generate correlated electron behavior. Pr-based “1-2-20” compounds with a Pr3+ non-Kramers doublet ground state in the crystalline electric field have been reported to exhibit quadrupolar Kondo phenomena, multipolar ordering, heavy fermion behavior, etc. In order to study the Fermi surface of PrT2Cd20 (T = Ni, Pd) compounds, we measured Shubnikov de Haas oscillations using the Proximity Detector Oscillator method for H up to 60 T at T = 1.5 K on single crystals. |
Wednesday, March 17, 2021 4:48PM - 5:00PM Live |
P43.00010: Fractionalized Fermi liquid in square-lattice Kondo-Heisenberg model Yung-Yeh Chang, Chung-Hou Chung, Alexei Tsvelik The Kondo-Heisenberg model on a (un-frustrated ) square lattice is studied via a controlled large-N (Sp(2N)) approach to demonstrate on a general ground the existence of a peculiar metallic state socalled“fractionalized Fermi liquid (FL*)” with unbroken translational symmetry and a Fermi surface volume not controlled by the total electron density. Close to half-filling, we show that the nesting of Fermi surface favors the Kondo hybridization to form between conduction electrons and local resonant-valence-bond spin-liquid fermions, which stabilizes FL* state with well-defined quasi-particle and gapped spinon excitations. The system develops an ordered phase at ground state (charge density wave or pair density wave superconducting). Our result generalizes the FL* state previously proposed in Phys. Rev. Lett. 90, 216403 (2003), which is restricted to frustrated Kondo lattice systems. |
Wednesday, March 17, 2021 5:00PM - 5:12PM Live |
P43.00011: Universality in the ferromagnetic strong coupling regime of the nonequilibrium Kondo model Adrian Culver, Natan Andrei We present a new method for calculating the time-dependent many-body wavefunction that follows a local quench. In the nonequilibrium Kondo model, we calculate the time-dependent wavefunction and the current-carrying nonequilibrium steady state that is the long time limit (with the system size taken to infinity first). We find a series expression for the steady state current; it agrees with standard leading order results in the usual weak antiferromagnetic regime. The series also allows the identification of a new universal regime of strong ferromagnetic coupling characterized by Kondo temperature TK(F) = D exp[ -(3π2/8)ρ|J| ] (J<0, ρ|J| →∞). In this regime, the differential conductance dI/dV reaches the unitarity limit 2e2/h asymptotically at large voltage or temperature [1]. |
Wednesday, March 17, 2021 5:12PM - 5:24PM Live |
P43.00012: Partial Kondo screening induced chiral d-wave superconductivity in a honeycomb lattice Hee Seung Kim, Hyeok-Jun Yang, SungBin Lee Kondo-Heisenberg model is one of the fascinating playground to study various phases, especially heavy (or fractionalized) Fermi liquid, Kondo singlet insulator, and superconductivity. We investigate the unconventional superconducting phases for the J1 -J2<span style="font-size:10.8333px"> </span>Kondo-Heisenberg model in a honeycomb lattice at a quarter filling. We analytically show that the d±id spinon pairing induces an electron pairing mediated by partial Kondo ordering, also resulting in the chiral superconductivity with non-trivial Chern number. Surprisingly, the inverse chirality on the electron sector is induced depending on the form of the Kondo order parameter. Finally, we propose the distinguished electric and thermal transport experiment signature of each phase. |
Wednesday, March 17, 2021 5:24PM - 5:36PM Live |
P43.00013: Possible multi-orbital ground state in CeCu2Si2 Andrea Marino, Andrea Amorese, Martin Sundermann, Kai Chen, zhiwei hu, Fadi Choukani, Philippe Ohresser, Javier Herrero-Martín, Stefano Agrestini, Chien-Te Chen, Hong-Ji Lin, Maurits Wim Haverkort, Silvia Seiro, Christoph Geibel, Frank Steglich, Liu Tjeng, Gertrud Zwicknagl, Andrea Severing The crystal-field ground state wave function of CeCu2Si2 has been investigated with linear polarized M-edge x-ray absorption spectroscopy from 250 mK to 250 K, thus covering the superconducting (Tc = 0.6 K), the Kondo (TK ≈ 20 K) as well as the Curie-Weiss regime. The comparison with full-multiplet calculations shows that the temperature dependence of the experimental linear dichroism is well explained with a Γ7(1) crystal-field ground state and the thermal population of excited states at around 30 meV. The crystal-field scheme does not change throughout the entire temperature range thus making the scenario of orbital switching unlikely. Spectroscopic evidence for the presence of the Ce 4f 0 configuration in the ground state is consistent with the possibility of a multi-orbital character of the ground state. We estimate from the Kondo temperature and crystal-field splitting energies that several percents of the higher lying Γ6 state and Γ7(2) crystal-field states are mixed into the primarily Γ7(1) ground state. This estimate is also supported by re-normalized band-structure calculations that use the experimentally determined crystal-field scheme. |
Wednesday, March 17, 2021 5:36PM - 5:48PM Live |
P43.00014: YbRh2Si2 nanodevices: fabrication and measurements Liyang Chen, dale lowder, Lukas Prochaska, Silke Buehler-Paschen, Douglas Natelson Below 70mK, YbRh2Si2, a heavy fermion compound, lies close to a magnetic field-tuned quantum critical point, between an antiferromagnetically ordered Fermi liquid phase and a paramagnetic Fermi liquid phase. This transition can be tuned via magnetic field along the c-axis. Although the zero field magnetic ordering temperature is very low, the non-Fermi liquid regime of quantum criticality persists over a broad temperature range. The understanding of electron transport and correlations in this non-Fermi liquid phase is comparatively unexplored. Here we present a process to fabricate YbRh2Si2 nanodevices using a SF6 dry etch, in which chromium hard masks are used to cover the designed pattern, and then removed by hydrochloric acid. The qualities of etched nanodevices are examined by measuring magnetoresistance and comparing with the unpatterned original film. We plan to study the electron correlations through measuring the shot noise in nanoscale constrictions, in both Fermi liquid and non-Fermi liquid regimes . We will also study the electronic phase coherence by measuring time dependent universal conductance fluctuations. |
Wednesday, March 17, 2021 5:48PM - 6:00PM Live |
P43.00015: Physical properties of Kondo lattice YbCuAs2 single crystal David Evans, Eundeok Mun YbCuAs2 compound crystallizes into a tetragonal ZrCuSi2-type structure. Magnetic susceptibility measurements for the YbCuAs2 polycrystalline sample showed an antiferromagnetic phase transition below 4 K. However, the neutron powder diffraction measurements of this sample didn’t show any additional Bragg peaks down to 1.5 K, indicating either there is no magnetic ordering down to 1.5 K or the ordered moment of Yb ions is smaller than the current experimental limit. We succeeded in growing single crystals of YbCuAs2 by high temperature ternary melt. Thermodynamic and transport properties were investigated by measuring the magnetization, electrical resistivity, and specific heat. In this talk, I will present thermodynamic and transport properties of Kondo lattice YbCuAs2 single crystal. |
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