Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session V27: Mixed Valence and Kondo Physics |
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Sponsoring Units: DCMP Chair: Priscilla Rosa, Los Alamos National Laboratory Room: 326 |
Thursday, March 17, 2016 2:30PM - 2:42PM |
V27.00001: The isostructural $\alpha-\gamma$ phase transition in Cerium: a DFT+DMFT study. Bernard Amadon, Thomas Applencourt, Alexis Gerossier, Jordan Bieder, Fabien Bruneval, Jules Denier \\ We present a study of the electronic structure and structural properties of the $\alpha-\gamma$ isostructural first order phase transition in cerium. Because of strong local electronic interactions due to 4f electrons, Density Functional Theory is not able to describe it. We thus use the combination of DFT and Dynamical Mean Field Theory, as implemented in ABINIT to understand and describe the transition:\\ Firstly, we use the constrained Random Phase Approximation to compute the effective interaction in cerium and discuss the validity of this approximation [1]. \\ Secondly, we use this interaction to clarify the orbital mechanism of the transition: we thus discuss the validity of different models [2]. \\ Thirdly, we compute the electronic free energy for the transition and discuss the role of entropy and spin orbit coupling [3,4]. \\ Finally, we put in perspective our results with respect to recent calculations. \\ [1] [1] B. Amadon, T. Applencourt, and F. Bruneval PRB 89, 125110 (2014) \\[2] [2] B. Amadon and A. Gerossier PRB 91, 161103(R) (2015)\\[3] [3] J. Bieder and B. Amadon PRB 89, 195132 (2014)\\[4] [4] B. Amadon, J. Denier and J. Bieder (unpublished) [Preview Abstract] |
Thursday, March 17, 2016 2:42PM - 2:54PM |
V27.00002: Simulation of the X-ray Emission Spectrum from Early Lanthanides Wei-ting Chiu, Chunjing Jia, Brian Moritz, Tom Devereaux, Magnus Lipp, Devon Mortensen, Gerald Seidler, Richard Scalettar For decades it has been known that certain Lanthanide metals, such as cerium and praseodymium, exhibit a volume collapse transition at a critical pressure. The volume change correlates with charge transfer from 4f orbitals to higher energy conduction bands due small differences in energy. To date, high pressure X-ray emission measurements have enabled the determination of the bare 4f moment of Lanthanide metals.\footnote{M. J. Lipp \textit{et al.}, PRL \textbf{109,} 195705(2012).} In particular at the $L_{\gamma_{1}}$ emission line, the intensity of a satellite peak captures the behavior of the 4f electrons across the volume collapse transition. Here we use exact diagonalization for an atomic model of the Lanthanides, including orbital site energies and core-, valence-, and conduction-band multiplet interactions to simulate the x-ray emission spectrum. The multiple interactions are derived from atomic structure calculations, augmented by effective 4f-to-conduction-band hybridization term. The Kondo screening effect from the conduction electrons at high pressure changes the 4f occupation, resulting in a change of the satellite peak intensity, which well reproduces the experimental findings in the early Lanthanide metals. [Preview Abstract] |
Thursday, March 17, 2016 2:54PM - 3:06PM |
V27.00003: Systematic investigation of structural, transport, magnetic and thermodynamic properties of hexagonal R$_2$Pt$_6$Al$_{15}$ (R = Y, La-Nd, Sm-Lu) series. Soham Manni, Q. Lin, S. L Bud'ko, P. C. Canfield We have synthesized single crystals of new hexagonal intermetallic series of compounds R$_2$Pt$_6$Al$_{15}$ with R = Y, La-Nd, Sm-Lu. Structural analysis have confirmed hexagonal $P6_3/mmc$ crystal structure with ordered R-site. Magnetic, transport and heat capacity measurements show that most of the members of the series order antiferromagnetically at low temperature with highest $T_N$ = 7.5 K for Gd$_2$Pt$_6$Al$_{15}$ and moments are along c-axis except Dy$_2$Pt$_6$Al$_{15}$ and Ho$_2$Pt$_6$Al$_{15}$. Ce$_2$Pt$_6$Al$_{15}$ does not order, but shows insulating behavior with a strong divergence in heat capacity divided by temperature ($C/T$). Mixed valence state of Eu$^{2+}$/Eu$^{3+}$ state has been observed in Eu$_2$Pt$_6$Al$_{15}$ with antiferromagnetic ordering below 3 K. Magnetic entropy and crystal electric field are analyzed for all the members from the magnetic contribution of heat capacity. This series of compounds serves a unique example of a rare earth series with only one rare earth (R) site having hexagonal point-symmetry. [Preview Abstract] |
Thursday, March 17, 2016 3:06PM - 3:18PM |
V27.00004: \textbf{Epitaxial growth and }\textbf{\textit{in situ}}\textbf{ ARPES of ultrathin YbAl}$_{\mathrm{\mathbf{3}}}$\textbf{ thin films} Shouvik Chatterjee, Darrell Schlom, Kyle Shen YbAl$_{\mathrm{3}}$ is a well-known intermediate valence compound that shows emergence of Fermi liquid behavior below a coherence temperature of \textasciitilde 34K -- 40K. Transport, thermodynamic and photoemission measurements have established limitations of Single Impurity Anderson model in describing this material system, suggesting the importance of lattice effects. However, microscopic mechanisms underlying these properties are yet to be properly understood, one reason being that the direct experimental determination of its electronic band structure is still lacking. In this talk I will present our recent efforts in stabilizing thin films of YbAl$_{\mathrm{3}}$ and \textit{insitu} angle-resolved photoemission spectroscopy (ARPES) of these films. With the aid of an Al buffer layer crystalline, phase pure and fully oriented epitaxial thin films can be grown with sub-nm surface roughness. By using ARPES, we, for the first time have been able to map out its band structure and Fermi surface. Moreover, by growing ultra thin films we have been able to drive this material system towards its 2D limit. Evolution of its electronic structure with temperature and dimensionality will be discussed. [Preview Abstract] |
Thursday, March 17, 2016 3:18PM - 3:30PM |
V27.00005: Entanglement entropy near Kondo-destruction quantum critical points Tathagata Chowdhury, Christopher Wagner, Kevin Ingersent, Jedediah Pixley Entanglement entropy is a measure of quantum-mechanical entanglement across the boundary created by partitioning a system into two subsystems. We study this quantity in Kondo impurity models that feature Kondo-destruction quantum critical points (QCPs). Recent work [1] has shown that the entanglement entropy between a Kondo impurity of spin $S_\mathrm{imp}$ and its environment is pinned at its maximum possible value $S_e=\ln(2S_{\mathrm{imp}}+1)$ throughout the Kondo phase. In the Kondo-destroyed phase, where the impurity spin acquires a nonzero expectation value $M_\mathrm{loc}$, $S_e = \ln(2 S_{\mathrm{imp}}+1)- a(S_{\mathrm{imp}}) M^2_\mathrm{loc}$ irrespective of the properties of the host. Here, we report numerical renormalization-group results for Kondo models with a pseudogapped density of states under a different partition that separates the impurity and on-site conduction electrons from the rest of the system. Now, the entanglement entropy is affected by the nature of the environment beyond the information contained in $M_{\mathrm{loc}}$, but $S_e$ still contains a critical part that exhibits power-law behavior in the vicinity of the Kondo-destruction QCP. [1] J. H. Pixley \emph{et. al.}, Phys. Rev. B \textbf{91}, 245122 (2015). [Preview Abstract] |
Thursday, March 17, 2016 3:30PM - 3:42PM |
V27.00006: Entanglement across different cuts along the Wilson chain for the pseudogap Anderson model Christopher Wagner, Tathagata Chowdhury, Kevin Ingersent, Jedediah Pixley Entanglement entropy measures the quantum entanglement of a pure state across the boundary created by partitioning a system into two subsystems. The entanglement entropy between an Anderson impurity and a pseudogapped conduction band displays nonuniversal behavior near the Kondo-destruction quantum critical point (QCP), but in the ordered phase contains a critical component proportional to the square of the order parameter [1]. Here we report calculations of the entanglement entropy for other partitions of the system. Specifically, within the numerical renormalization group formulation of the problem, we consider partitions where one subsystem is composed of the impurity plus the first few sites in the Wilson-chain representation of the conduction band, sites that represent the electronic states spatially localized closest to the impurity. By calculating the reduced density matrix for the subsystem containing the impurity, we study the behavior of the entanglement entropy across the parameter space of the model, with particular focus on the vicinity of the Kondo-destruction QCP. [1] J. H. Pixley, T. Chowdhury, M. T. Miecnikowski, J. Stephens, C. Wagner, and K. Ingersent, Phys. Rev. B 91, 245122 (2015) [Preview Abstract] |
Thursday, March 17, 2016 3:42PM - 3:54PM |
V27.00007: Skyrmion defects of antiferromagnet and competing singlet orders of a Kondo-Heisenberg model on honeycomb lattice Chia-Chuan Liu, Pallab Goswami, Qimiao Si The competition between antiferromagnetism and proximate singlet orders is the common feature of many heavy fermion compounds. Depending on the context, the singlet order can be described by static Kondo singlets, unconventional superconductivity, site or bond centered charge orders, or more exotic density waves. This competition between singlet and triplet orders can give rise to exotic quantum critical points or even an intervening non-Fermi liquid phase. It is a fundamentally important but challenging problem to develop a general scheme for identifying the competing singlet orders from the antiferromagnetically ordered side and vice versa. We study this problem on a honeycomb lattice, and approach it starting from the Kondo-destroyed antiferromagnetic phase. We show how the topological defects of the antiferromagnetic order parameter can give rise to competing singlet orders in the presence of itinerant fermions. We identify translational symmetry breaking singlet orders and static Kondo singlets as gapped collective excitations inside the skyrmion core. Our results provide non-perturbative insight into the global phase diagram of heavy fermion compounds. [Preview Abstract] |
Thursday, March 17, 2016 3:54PM - 4:06PM |
V27.00008: Charge density wave instability in the periodic Anderson model with electron-phonon interaction Enzhi Li, Peng Zhang, Ka-Ming Tam, Shuxiang Yang, Juana Moreno, Mark Jarrell We study the periodic Anderson model with the conduction electrons coupled to phonons. It has been shown by using the dynamical mean field theory that the model contains two phases, the Kondo singlet phase for strong hybridization and the local moment phase for weak hybridization. In the hybridization-temperature plane, these two phases are separated by a first order phase transition line which terminates at a second order phase transition point. We calculated the susceptibilities for various possible orderings for the model. We found that the charge density wave ordering is robust at low temperature and for weak hybridization. The second order critical point is screened out by the formation of CDW. It is probable that the two phases should be Kondo singlet phase and CDW phase. [Preview Abstract] |
Thursday, March 17, 2016 4:06PM - 4:18PM |
V27.00009: The entanglement structure of the Kondo singlet in energy space Chun Yang, Adrian Feiguin We unveil the entanglement structure of the Kondo singlet in energy space by studying the contribution of each individual free electron eigenstate. This is a problem of two spins coupled to a bath, where the bath is formed by the remaining conduction electrons. Being a mixed state, we resort to the ''concurrence'' as a good measure of entanglement. Using the density matrix renormalization group and analytical variational calculations with the Yoshida wave-function, and slave bosons, we find a distinct transition between weak and strong coupling regimes characterized by very different entanglement distributions. We discuss implications to the theory of the Kondo cloud. [Preview Abstract] |
Thursday, March 17, 2016 4:18PM - 4:30PM |
V27.00010: Kondo phase shift at the zero-bias anomaly of quantum point contacts Boris Brun, Frederico Martins, Sébastien Faniel, Benoit Hackens, Antonella Cavanna, Christian Ulysse, Albdelkarim Ouerghi, Ulf Gennser, Dominique Mailly, Pascal Simon, Serge Huant, Vincent Bayot, Marc Sanquer, Hermann Sellier The Kondo effect is the many-body screening of a local spin by a cloud of electrons at very low temperature. It has been proposed as an explanation of the zero-bias anomaly in quantum point contacts where interactions drive a spontaneous charge localization. However, the Kondo origin of this anomaly remains under debate, and additional experimental evidence is necessary. Here we report on the first phase-sensitive measurement of the zero-bias anomaly in quantum point contacts using a scanning gate microscope to create an electronic interferometer. We observe an abrupt shift of the interference fringes by half a period in the bias range of the zero-bias anomaly, a behavior which cannot be reproduced by single-particle models. We instead relate it to the phase shift experienced by electrons scattering off a Kondo system. Our experiment therefore provides new evidence of this many-body effect in quantum point contacts. [Preview Abstract] |
Thursday, March 17, 2016 4:30PM - 4:42PM |
V27.00011: Full counting statistics for current through each channel of orbital degenerate Anderson impurity with exchange interactions Rui Sakano, Akira Oguri, Yunori Nisikawa We study non-equilibrium currents, current fluctuations and cross-correlations of the currents through Kondo-correlated quantum dots at low applied bias-voltages, using full counting statistics. To elucidate impact of dot-site interaction to these current properties in crossover between noninteracting and some Kondo states, renormalized perturbation theory or local Fermi liquid theory are employed. The exact form of the cumulant generating function up to third order of bias-voltage is derived in term of renormalized parameters. Specifically, crossover behavior of the Fano factor (ratio between noise and current) and current crosscorrelations for two-fold orbital case is discussed with using computed renormalized parameters by numerical renormalization group. [Preview Abstract] |
Thursday, March 17, 2016 4:42PM - 4:54PM |
V27.00012: Voltage quench dynamics of a Kondo system Andrey Antipov, Qiaoyuan Dong, Emanuel Gull We examine the dynamics of a correlated quantum dot in the mixed valence regime. We perform numerically exact calculations of the current after a quantum quench from equilibrium by rapidly applying a bias voltage in a wide range of initial temperatures. The current exhibits short equilibration times and saturates upon the decrease of temperature at all times, indicating Kondo behavior both in the transient regime and in steady state. The time-dependent current saturation temperature connects the equilibrium Kondo temperature to a substantially increased value at voltages outside of linear response. These signatures are directly observable by experiments in the time-domain. [Preview Abstract] |
Thursday, March 17, 2016 4:54PM - 5:06PM |
V27.00013: NMR spin relaxation rates in the Heisenberg bilayer Tiago Mendes, Nicholas Curro, Richard Scalettar, Thereza Paiva, Raimundo R. dos Santos One of the striking features of heavy fermions is the fact that in the vicinity of a quantum phase transition these systems exhibit the breakdown of Fermi-liquid behavior and superconductivity. Nuclear magnetic resonance (NMR) expirements play an important role in the study of these phenomena. Measurements of NMR spin relaxation rates and Knight shift, for instance, can be used to probe the electronic spin susceptibility of these systems. Here we studied the NMR response of the Heisenberg bilayer model. In this model, it is well known that the increase of the interplane coupling between the planes, $J_{perp}$, supresses the antiferromagnetic order at a quantum critical point (QCP). We use stochastic series expansion (SSE) and the maximum-entropy analytic continuation method to calculate the NMR spin lattice relaxation rate $1/T_1$ and the spin echo decay $1/T_{2G}$ as function of $J_{perp}$. The spin echo decay, $T_{2G}$ increases for small $J_{perp}$, due to the increase of the order parameter, and then vanishes abruptly in the QCP. The effects of $J_{perp}$ dilution disorder in the QCP and the relaxation rates are also discussed. This research was supported by the NNSA grant number DE-NA 0002908, and Ci\^encia sem fronteiras program/CNPQ. [Preview Abstract] |
Thursday, March 17, 2016 5:06PM - 5:18PM |
V27.00014: 4f metals (compounds) under High Pressure (and Temperature): f-electron Correlation Physics Magnus Lipp, Zsolt Jenei, Hyunchae Cynn, William Evans The physics of 4f-electron correlation governs the behavior of the most interesting group in the periodic table, the rare-earth elements. Arguably the most celebrated example is cerium with its iso-structural (fcc) volume collapse (VC) from the $\gamma $- to the $\alpha $-phase ending in a critical point. Close to the VC cerium is even auxetic since its Poisson's ratio becomes negative. Radiography tells us that both phases continue on into the melt, possibly separated by a first order transition. The presence of the f-electron can be interrogated via X-ray emission spectroscopy of the satellite intensity of the L$\gamma $ radiation. Across the VC it experiences a step-like drop which could be interpreted as a discontinuous decrease of the \textit{4f}-moment or occupancy. The theoretical models (Hubbard-Mott or Kondo) explain these phenomena with the behavior of the f-electrons themselves or their spin but the contribution of the lattice-phonons also plays an important part. However, its share in the entropy change across the VC decreases with temperature. This work was performed under the auspices of the US DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The X-ray studies were performed at HPCAT (Sector 16), APS/ANL. HPCAT is supported by CIW, CDAC, UNLV and LLNL through funding from~DOE-NNSA, DOE-BES and NSF. APS is supported by DOE-BES, under Contract No. DE-AC02-06CH11357. [Preview Abstract] |
Thursday, March 17, 2016 5:18PM - 5:30PM |
V27.00015: Multi-pole orders and Kondo screening: Implications for quantum phase transitions in multipolar heavy-fermion systems Hsin-Hua Lai, Emilian Nica, Qimiao Si Motivated by the properties of the heavy-fermion Ce3Pd20Si6 compound [1] which exhibits both antiferro-magnetic (AFM) and antiferro-quadrupolar (AFQ) orders, we study a simplified quantum non-linear sigma model for spin-1 systems [2], with generalized multi-pole Kondo couplings to conduction electrons [3]. We first consider the case when an SU(3) symmetry relates the spin and quadrupolar channels. We then analyze the effect of breaking the SU(3) symmetry, so that the interaction parameters in the spin and quadrupolar sectors are no longer equivalent, and different stages of Kondo screenings are allowed. A renormalization group analysis [4] is used to analyze the interplay between the Kondo effect and the AFM/AFQ orders. Our work paves the way for understanding the global phase diagram in settings beyond the prototypical spin-½ cases. We also discuss similar considerations in the non-Kramers systems such as the heavy fermion compound PrV2Al20 [5]. [1]Custers et al, Nat.Mater. 11, 189 (2012). [2]A. Smerald et. al., Phys. Rev. B 88, 184430 (2013);Phys. Rev. B 91, 174402 (2015). [3]O. Parcollet et. al,, Phys. Rev. Lett. 79, 4665 (1997);Phys. Rev. B 58, 3794 (1998) [4]Yamamoto S.J. and Q. Si, Phys. Rev. B 81, 205106 (2010). [5]Y. Shimura et. al., Phys. Rev. B 91, 241102(R) (2015) [Preview Abstract] |
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