Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session R19: Kondo Screening  Different Aspects 
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Sponsoring Units: DCMP Chair: Piers Coleman, Rutgers University Room: 321 

R19.00001: ABSTRACT WITHDRAWN 
Wednesday, March 20, 2013 2:42PM  2:54PM 
R19.00002: BerezinskiiKosterlitzThouless Transition in Heavy Fermion Superlattices JianHuang She, Alexander Balatsky We propose an explanation of the superconducting transitions discovered in the heavy fermion superlattices by Mizukami et al. (Nature Physics 7, 849 (2011)) in terms of BerezinskiiKosterlitzThouless transition. We observe that the effective mass mismatch between the heavy fermion superconductor and the normal metal regions provides an effective barrier that enables quasi 2D superconductivity in such systems. We show that the resistivity data, both with and without magnetic field, are consistent with BKT transition. Furthermore, we study the influence of a nearby magnetic quantum critical point on the vortex system, and find that the vortex core energy can be significantly reduced due to magnetic fluctuations. Further reduction of the gap with decreasing number of layers is understood as a result of pair breaking effect of Yb ions at the interface. Reference: JianHuang She, Alexander V. Balatsky, Phys. Rev. Lett. 109, 077002 (2012) [Preview Abstract] 
Wednesday, March 20, 2013 2:54PM  3:06PM 
R19.00003: Theory for ESR in the heavy fermion system $\beta$YbAlB$_4$ Aline Ramires, Piers Coleman We propose a theory to explain the unusual temperature dependence of the Electron Spin Resonance (ESR) lines of the critical heavy fermion superconductor $\beta$YbAlB$_{4}$. This system shows a conduction electron ESR signal at high temperatures, but at low temperatures its gfactor shifts to the felectron gfactor and it develops strong anisotropy. With our theory we are able to explain this dichotomy based on the fact that the lower crystal field configuration of the local moments in this system is a pure $\pm 5/2\rangle$. Because of its Ising nature these spins can not be directly probed by ESR, and the felectron features that appear at low temperatures can be explained by an emergent hybridization model. We can account for the origin of this signal and its main characteristics qualitatively, including gfactor shift and the hyperfine structure with the assumption that the scattering rate is unusually small. [Preview Abstract] 
Wednesday, March 20, 2013 3:06PM  3:18PM 
R19.00004: Effects of correlated hybridization in the singleimpurity Anderson model Valter L\'Ibero, Rodrigo Veiga The development of new materials often dependents on the theoretical foundations which study the microscopic matter, i.e., the way atoms interact and create distinct configurations. Among the interesting materials, those with partially filled $d$ or $f$ orbitals immersed in nonmagnetic metals have been described by the Anderson model, which takes into account Coulomb correlation ($U$) when a local level (energy $E_d$) is doubled occupied, and an electronic hybridization between local levels and conduction band states. In addition, here we include a correlated hybridization term, which depends on the locallevel occupation number involved. This term breaks particlehole symmetry (even when $U+2E_d=0$), enhances charge fluctuations on local levels and as a consequence strongly modifies the crossover between the Hamiltonian fixedpoints, even suppressing one or other. We exemplify these behaviors showing data obtained from the Numerical Renormalization Group (NRG) computation for the impurity temperaturedependent specific heat, entropy and magnetic susceptibility. The interleaving procedure is used to recover the continuum spectrum after the NRGlogarithmic discretization of the conduction band. [Preview Abstract] 
Wednesday, March 20, 2013 3:18PM  3:30PM 
R19.00005: Fridel sum rules for one and twochannel Kondo models and unitarity paradox via bosonizationrefermionization approach Maxim Kharitonov, Natan Andrei, Piers Coleman We calculate the singleparticle Green's functions and scattering amplitudes of the onechannel and channelanisotropic twochannel Kondo models at the Toulouse and EmeryKivelson lines, respectively, where exact solutions via the bosonizationrefermionization approach are admitted. We demonstrate that in this approach the Friedel sum rules  the relations between the trapped spin and ``flavor'' moments and the scattering phase shifts in the Fermiliquid regime  arise naturally and elucidate on their subtleties. We also recover the ``unitarity paradox'' [1,2]  the vanishing of the singleparticle scattering amplitude at the channelsymmetric point of the twochannel Kondo model  stemming from nonFermiliquid behavior. We discuss the implications of these results for the development of composite pairing in heavy fermion systems.\\[4pt] [1] A. W. W. Ludwig and I. Affleck, Phys. Rev. Lett. 67, 3160 (1991).\\[0pt] [2] J. M. Maldacena and A. W. W. Ludwig, Nucl. Phys. B. 506, 565 (1997). [Preview Abstract] 
Wednesday, March 20, 2013 3:30PM  3:42PM 
R19.00006: Kondo destruction and superconducting correlations in the twoimpurity BoseFermi Anderson model Lili Deng, Kevin Ingersent, Jedediah Pixley, Qimiao Si The BoseFermi Kondo and Anderson models are among the simplest models for Kondo destruction, the phenomenon believed to underly the anomalous physics of certain heavyfermion materials near the border of magnetism. With the goal of probing superconductivity near the Kondodestruction local quantum critical point of the Kondo lattice, here we study the twoimpurity Anderson model supplemented both by an interimpurity exchange of either SU(2) or Ising symmetry and by a linear coupling between the impurity spins and a subOhmic bosonic bath. Using the continuoustime quantum Monte Carlo method and the numerical renormalization group, we elucidate the phase diagram arising from the interplay of Kondo physics, interimpurity exchange (ferromagnetic or antiferromagnetic), and bosonic decoherence, and demonstrate the existence of a Kondodestruction quantum critical point in the model. We investigate the properties near this quantum critical point, as well as the effect of a critical suppression of the Kondo effect on superconducting pairing correlations. [Preview Abstract] 
Wednesday, March 20, 2013 3:42PM  3:54PM 
R19.00007: Quasiparticle scattering spectroscopy (QPS) of Kondo lattice heavy fermions L.H. Greene, S.M. Narasiwodeyar, P. Banerjee, W.K. Park, E.D. Bauer, P.H. Tobash, R.E. Baumbach, F. Ronning, J.L. Sarrao, J.D. Thompson Pointcontact spectroscopy (PCS) is a powerful technique to study electronic properties via measurements of nonlinear currentvoltage characteristic across a ballistic junction. It has been frequently adopted to investigate novel and/or unconventional superconductors by detecting the energydependent Andreev scattering. PCS of nonsuperconducting materials has been much rarely reported. From our recent studies on heavy fermions [1], we have frequently observed strongly biasdependent and asymmetric conductance behaviors. Based on a Fano resonance model in a Kondo lattice [2], we attribute them to energydependent quasiparticle scattering off hybridized renormalized electronic states, dubbing it QPS. We will present our QPS results on several heavyfermion systems and discuss QPS as a novel technique to probe the bulk spectroscopic properties of the electronic structure. For instance, it reveals that the hybridization gap in URu$_{2}$Si$_{2}$ opens well above the hidden order transition [1].\\[4pt] [1] W. K. Park \textit{et al}., PRL \textbf{108}, 246403 (2012); \textit{ibid.,} \textbf{100}, 177001 (2008).\\[0pt] [2] M. Maltseva, M. Dzero, P. Coleman, PRL \textbf{103}, 206402 (2009). [Preview Abstract] 
Wednesday, March 20, 2013 3:54PM  4:06PM 
R19.00008: Quantum Phases of the ShastrySutherland Kondo Lattice Jedediah Pixley, Rong Yu, Qimiao Si Motivated by the discovery of the geometrically frustrated heavy fermion metal Yb2Pt2Pb[1], which has a quasi two dimensional ShastrySutherland lattice structure, we consider the HeisenbergKondo lattice model on a two dimensional ShastrySutherland geometry. Using a largeN method, we obtain the phase diagram and, in particular, the quantum transitions between a valence bond solid phase and a heavy Fermi liquid phase. Interestingly, we find intermediate states that break the C4 symmetry. We discuss the implications of our results for the experiments on Yb2Pt2Pb and related 221 materials [1], as well as the possible placement of these systems in a proposed global phase diagram for heavy fermion metals [2]. [1] M. S. Kim and~M. C. Aronson, arXiv:1202.0220 (2012). [2] Q. Si, Phys. Status Solidi B 247, 476484 (2010). [Preview Abstract] 
Wednesday, March 20, 2013 4:06PM  4:18PM 
R19.00009: Kondo hole route to incoherence in the periodic Anderson model Pramod Kumar, N.S. Vidhyadhiraja The interplay of disorder and interactions in strongly correlated electronic systems is a subject of perennial interest. In this work, we have investigated the effect of Kondohole type disorder on the dynamics and transport properties of heavy fermion systems. We employ the periodic Anderson model within the framework of coherent potential approximation and dynamical mean field theory. The crossover from lattice coherent behaviour to an incoherent singleimpurity behaviour is reflected in all aspects: a highly frequency ($\omega$)dependent hybridization becomes almost flat, the coherence peak in resistivity (per impurity) gives way to a Hammann form that saturates at low temperature ($T$); the Drude peak and the midinfrared peak in the optical conductivity vanish almost completely. The zero temperature resistivity can be captured in a closed form expression, and we show how the Nordheim's rule gets strongly modified in these systems. The thermopower exhibits a characteristic peak, which changes sign with increasing disorder, and its location is shown to correspond to the low energy scale of the system ($\omega_L$). In fact, the thermopower appears to be much more sensitive to disorder variations than the resistivity. A comparison to experiments yields quantitative agreement. [Preview Abstract] 
Wednesday, March 20, 2013 4:18PM  4:30PM 
R19.00010: BoseFermi Kondo model with a local transverse field and its implications for the global phase diagram of heavy fermions Emilian Nica, Qimiao Si, Kevin Ingersent Recent studies of the global phase diagram of quantum critical heavy fermion metals [1] have motivated us to consider the interplay between the quantum fluctuations within the localmoment system and those associated with the Kondo interaction. Towards this goal, we studied a BoseFermi Kondo model with Ising anisotropy in the presence of a local transverse field. Using the numerical renormalization group method for coexisting fermionic and bosonic baths [2], we found that tuning the transverse field gives rise to a continuous phase transition between a local moment phase and a Kondo screened phase. We determine the critical fixed point structure by studying the transitions accessed by varying the transverse field for different initial values of the coupling to the dissipative boson bath. Finally, we discuss the implications of these results for the global phase diagram of the Kondo lattice.\\[4pt] [1] Q. Si and F. Steglich, Science 329, 1161 (2010).\\[0pt] [2] M. T. Glossop and K. Ingersent, Phys. Rev. B 75, 104410 (2007) [Preview Abstract] 
Wednesday, March 20, 2013 4:30PM  4:42PM 
R19.00011: Kondo Metal and Ferrimagnetic Insulator on the Triangular Kagome Lattice YaoHua Chen, HongShuai Tao, DaoXin Yao, WuMing Liu We obtain the rich phase diagrams in the Hubbard model on the triangular kagome lattice as a function of interaction, temperature and asymmetry, by combining the cellular dynamical meanfield theory with the continuous time quantum Monte Carlo method. The phase diagrams show the asymmetry separates the critical points in Mott transition of two sublattices on the triangular kagome lattice and produces two novel phases called plaquette insulator with a clearly visible gap and a gapless Kondo metal. When the Coulomb interaction is stronger than the critical value $U_c$, a short range paramagnetic insulating state emerges before the ferrimagnetic order is formed independent of asymmetry. Furthermore, we discuss how to measure these phases in future experiments. [Preview Abstract] 
Wednesday, March 20, 2013 4:42PM  4:54PM 
R19.00012: Doniach Diagram in Disordered Electrons System Hyunyong Lee, Stefan Kettemann We have derived the quantum phase diagram of disordered electron systems with magnetic impurities. The competition between RKKY interaction, $J_{RKKY}$, and Kondo effect gives rise to a rich quantum phase diagram, or Doniach diagram. We present numerical results for disordered 2D electron systems which show that both Kondo temperature, $T_K$ and $J_{RKKY}$ are widely distributed and quantum critical point is extended to a critical region. We find a sharp cutoff in the distribution of their ratio, $J_{RKKY}/T_K$, and from that critical density of magnetic impurity below which Kondo always wins. We find that the spin coupled phase grows at the expense of Kondo phase as increasing disorder.The spin coupled phase shows a succession of 3 phases: 1. a Griffiths phase with anomalous power laws determined by distribution of $J_{RKKY}$, 2. spin glass phase, 3. long range magnetic ordered phase. We report the results on graphene where we find that spin coupled phase is more stable against Kondo screening, but is more easily destroyed by disorder into a paramagnetic phase [1].\\[4pt] [1] H. Lee, S. Kettemann, arXiv:1211.1734(2012) [Preview Abstract] 
Wednesday, March 20, 2013 4:54PM  5:06PM 
R19.00013: Transport properties of a two impurity system: a theoretical approach. Ignacio J. Hamad, Laercio Costa Ribeiro, George Martins, Enrique V. Anda Double magneticimpurity systems have attracted great attention due to their rich physics and possible technological applications. A system of two interacting Co atoms has been studied in a recent STM experiments (Nature Physics {\bf 7}, 901 (2011)). The precise control of the interimpurity distance made it possible to explore in detail the transport properties of the system as a function of the impurities' interaction with each other. We explain, for all the parameter range studied, the physics observed in the experiments using a microscopic model, based on the two impurity Anderson model, including a twopath geometry for charge transport. The manybody system is treated in the finiteU Slave Boson Mean Field Approximation. Other results obtained using the Logarithmic Discretization Embedded Cluster Approximation are also discussed. We physically characterize the system and show that, as in the experiments, the features observed in the transport properties depend on the presence of two impurities but also on the existence of two conducting channels for electron transport. In particular, we obtain a splitting in the differential conductance, compatible with the one observed in the experiments, as a result of the superposition of the manybody Kondo states of each impurity. [Preview Abstract] 
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