Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C20: Heavy Fermions and Interacting felectron Materials 
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Sponsoring Units: DCMP Chair: Rico Schoenemann, National High Magnetic Field Laboratory: Florida State University Room: 280 
Monday, March 13, 2017 2:30PM  2:42PM 
C20.00001: Direct measurement of the localized  itinerant transition, hybridization and spin density waves transition of 5f electrons. ShiYong Tan, DongHua Xie, XinChun Lai In heavyfermion compounds, f electrons show both itinerant and localized behavior depending on the external conditions, and the hybridization between localized f electrons and itinerant conduction bands gives rise to their exotic properties like heavyfermions, magnetic orders and unconventional superconductivity. Duo to the risk of handling radioactive actinide materials, the direct experimental evidence of the band structure evolution across the localized to itinerant and magnetic transition for 5f electrons is lacking. Here, by using angleresolved photoelectron spectroscopy, we revealed the dual nature (localized vs itinerant) and the development of two kinds of heavy quasiparticles bands of 5f electrons in antiferromagnetic USb2. Partially opened energy gaps were observed on one quasiparticle 5f band cross the AFM transition around 203K, indicating that the magnetic orders in USb2 are of spin density waves (SDW) type similar to Cr. The localized 5f electrons and itinerant conduction bands hybridize to form another heavy quasiparticles band at around 120K, and then open hybridization gaps at even lower temperature. Our results provide direct spectral demonstration of the localized itinerant transition, hybridization and SDW transition of 5f electrons for uraniumbased materials. [Preview Abstract] 
Monday, March 13, 2017 2:42PM  2:54PM 
C20.00002: Emergent magnetic anisotropy in cubic CeIn$_3$ Filip Ronning, Philip Moll, Toni Helm, Neil Harrison, Ross McDonald, Laurel Winter, Fedor Balakirev, Eric Bauer, Bertram Batlogg, Shangshun Zhang, Cristian Batista Metals containing cerium exhibit a diverse range of fascinating phenomena including heavy fermion behavior, quantum criticality, and novel states of matter such as unconventional superconductivity. Because spinorbit coupling and crystal field energy scales are large relative to the energy scales of the associated phenomena it is generally believed to be safe to assume that the interactions between the felectrons are spherically symmetric in spin space. By using magnetic fields with strengths comparable to the crystal field energy scale we illustrate the breakdown of the spherical approximation in the prototypical cubic heavy fermion material CeIn$_3$, which also displays unconventional superconductivity near a quantum critical point under applied pressure. Above 40 T, the HT phase diagram develops a surprising anisotropy. This work illustrates that magnetic fields can tune the effective hybridization and exchange interactions potentially leading to new exotic field tuned effects in fbased materials. [Preview Abstract] 
(Author Not Attending)

C20.00003: Pressuredriven 4 f localizeditinerant crossover in heavyfermion compound CeIn3: A firstprinciples manybody perspective Haiyan Lu, Li Huang The localizeditinerant nature of Ce4$f$ valence electrons in heavy fermion compound CeIn$_{3}$ under pressure is studied thoroughly by means of the combination of density functional theory and singlesite dynamical meanfield theory. The detailed evolutions of electronic structures of CeIn$_{3}$, including total and partial density of states, momentumresolved spectral functions, and valence state histograms are calculated in a wide pressure range where the corresponding $V/V_0 \in [0.6,1.0]$ (here $V_0$ is the experimental crystal volume) at $T \cong 116$ K. Upon increasing pressure, two strong peaks associated with the Ce$4f$ states emerge near the Fermi level, and the $c$$f$ hybridization and valence state fluctuation are enhanced remarkably. Moreover, the kinetic and potential energies rise, while the occupancy, total angular momentum, and lowenergy scattering rate of the Ce$4f$ electrons decline with respect to pressure. All the physical observables considered here exhibit prominent kinks or fluctuations in $V/V_0 \in [0.80,0.90]$, which are probably the desired fingerprints for the Ce4$f$ localizeditinerant crossover. [Preview Abstract] 
Monday, March 13, 2017 3:06PM  3:18PM 
C20.00004: Spin reorientation in heavy fermion system $\alpha YbAl_{1x} Fe_{x} B_{4} $ Shan Wu, C. Broholm, K. Kuga, Shintaro Suzuki, S. Nakatsuji, M. Mourigal, M. Stone, Wei Tian, Y. Qiu, Jose RodriguezRivera Non centrosymmetric $\alpha YbAlB_{4} $ has a heavy Fermi liquid ground state and shares many characteristics with centrosymmetric $\beta YbAlB_{4} $. Both isomorphs display intermediate valence, associated with a fluctuation scale of $T_{0} =$ 200 K and a Kondo lattice scale of $T^{\ast }=$ 8 K[1]. Unlike $\beta YbAlB_{4} $, $\alpha YbAlB_{4} $ is at the boundary of a transition from a Fermi liquid metallic state to an antiferromagnetic (AFM) insulating state, driven by Fe substitution of Al [2]. Magnetization and specific heat measurements reveal two different antiferromagnetic phases with $T_{N} =$ 9 K and $T_{N} =$ 2 K for Fe concentration above and below x$=$0.07. We report single crystal neutron scattering experiments on Fe doped YbAlB$_{4}$ with x$=$0.035 and x$=$0.125. While the ordering wave vector is identical,$\vec{{k}}=(1,0,0)$, the spin orientation switches from $c$ to $a$ with increasing Fe concentration. This suggests different anisotropic hybridization between 4f and conduction electrons that we confirmed by determining the crystal field levels. [1] M. Okawa et al., PRL 104, 247201 (2010) [2] K. Kuga, S. Nakatsuji PRB 86, 224413 (2012) [Preview Abstract] 
Monday, March 13, 2017 3:18PM  3:30PM 
C20.00005: The heavy fermion compound YbCu4Cd. Eundeok Mun, Hyuna Park We reinvestigate the physical properties of YbCu$_{\mathrm{4}}$Cd single crystals. It has been shown that both YbCu$_{\mathrm{4}}$Ag and YbCu$_{\mathrm{4}}$Cd compounds have nearly the same Kondo temperature \textasciitilde 200 K. The magnetic susceptibility of YbCu$_{\mathrm{4}}$Ag shows a peak structure around 40 K, whereas a paramagnetism appears in YbCu$_{\mathrm{4}}$Cd. To elucidate the discrepancies in low temperature magnetic susceptibility data, single crystals of YbCu$_{\mathrm{4}}$Cd were grown by using Cd richer compositions. We show that the magnetic susceptibility of YbCu$_{\mathrm{4}}$Cd is sensitive to the growth conditions. The thermodynamic and transport properties of YbCu$_{\mathrm{4}}$Cd have been reinvestigated by means of magnetic susceptibility, magnetization, electrical resistivity, Hall effect, and specific heat measurements. [Preview Abstract] 
Monday, March 13, 2017 3:30PM  3:42PM 
C20.00006: Effects of a magnetic field on the fragile antiferromagnetism of the heavyfermion YbBiPt B. G. Ueland, A. Kreyssig, J. W. Lynn, L. W. Harriger, K. Prok\v{e}s, E. D. Mun, S. Sauerbrei, S. M. Saunders, S. L. Bud'ko, R. J. McQueeney, P. C. Canfield, A. I. Goldman YbBiPt is a cubic superheavyfermion compound possessing antiferromagnetic (AFM) order below $T_N=0.4$~K, and a quantum critical point at a magnetic field of $H_c\approx0.4$~T. The order is characterized by a propagation vector of $\tau_m=(\frac{1}{2},\frac{1}{2},\frac{1}{2})$, with the ordered moment aligned along $\tau_m$. Here, we present results from neutron scattering experiments performed while applying a magnetic field along various crystal directions. We find that the intensity of the magnetic scattering at $(\frac{1}{2},\frac{1}{2},\frac{3}{2})$ increases when a field is applied along the $(1,1,0)$ direction, and reaches a maximum at $\approx0.6$~T. With the field along $(0,0,1)$, the scattering intensity smoothly decreases with increasing field. For the field along $(1,1,0)$, the intensity is constant up to $\approx0.6$~T and then decreases. We explain our results by considering the orientations of the magnetic domains with respect to the applied field. Work at the Ames Laboratory was supported by the Department of Energy, Basic Energy Sciences under Contract No. DEAC0207CH11358. This research is funded in part by the Gordon and Betty Moore Foundationâ€™s EPiQS Initiative through Grant GBMF4411. [Preview Abstract] 
Monday, March 13, 2017 3:42PM  3:54PM 
C20.00007: Thermodynamic and electrical transport properties of the layered triangular Ce lattice compound CeAuAl4Ge2 Shengzhi Zhang, Andrew Gallagher, You Lai, David Graf, Tiglet Besara, Kuanwen Chen, Theo Siegrist, Laura Greene, Ryan Baumbach We report electronic and magnetic properties of single crystalline CeAuAl$_{\mathrm{4}}$Ge$_{\mathrm{2}}$. This compound crystallizes in a rhombohedral structure (S.G. {\#}166) and may host geometrical magnetic frustration on the Ce sublattice. Electrical transport measurements show metallic behavior with a small residual resistivity ($\rho_{\mathrm{0}}$ $=$ 3 $\mu \Omega $cm). Quantum oscillations are seen in the ac magnetic susceptibility, which uncover a threedimensional Fermi surface. Weak hybridization between the f and conduction electron states is indicated by the simplemetallic temperature dependence of the electrical resistivity, the small electronic coefficient of the heat capacity, and the small charge carrier effective masses ($m$* $\approx $ 0.4  1 $m_{\mathrm{e}})$. As evidenced by the magnetic susceptibility, there is an appreciable difference between the CurieWeiss temperature ($\Theta \quad \approx $ 90 K) and the onset of the magnetic ordering temperature ($T_{\mathrm{M}} \quad =$ 1.4 K), suggesting that magnetic frustration dominates the magnetic behavior. We will discuss the prospects for studying magnetic frustration in a simple metallic environment, and for tuning the magnetic ordering towards a frustrated quantum phase transition. [Preview Abstract] 
Monday, March 13, 2017 3:54PM  4:06PM 
C20.00008: Nuclear magnetic resonance investigation of the novel heavy fermion system Ce$_{2}$CoAl$_{7}$Ge$_{4}$ Adam Dioguardi, Pedro Guzman, Nirmal Ghimire, Stuart Brown, Joe Thompson, Eric Bauer, Filip Ronning We present nuclear magnetic resonance (NMR) measurements performed on single crystalline Ce$_{2}$CoAl$_{7}$Ge$_{4}$. This material is a member of a recently discovered family of heavy fermion materials Ce$_{2}$MAl$_{7}$Ge$_{4}$, where M $=$ Co, Ir, Ni, or Pd that crystallize in the noncentrosymmetric tetragonal space group P4 21m. Previous measurements indicated a strong Kondo interaction, as well as magnetic ordering at 1.75 K. Our $^{59}$Co NMR spectral measurements reveal a Knight shift anomaly at T* \textasciitilde 17.5 K for H$_{0}$ \textbar \textbar c, and 12.5 K for H$_{0}$ \textbar \textbar a associated with felectron conduction electron coherence. Spinlattice relaxation rate measurements indicate diverging spin fluctuations at a magnetic ordering temperature of 1.6 K. An analysis of the Korringa enhancement factor suggests that the character of the spin fluctuations is dominantly ferromagnetic. [Preview Abstract] 
Monday, March 13, 2017 4:06PM  4:18PM 
C20.00009: Electronic structure and properties of heavy fermion system CeAuBi$_{\mathrm{2}}$ Matteo Michiardi, Fabio Boschini, Elia Razzoli, Giorgio Levy, Ilya Elfimov, Andrea Damascelli, Soren Ulstrup, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Halyna Hodovanets, Chris Eckberg, Johnpierre Paglione Rareearth intermetallic compounds are an excellent platform to realize a variety of physical phenomena stemming from strong electron correlation, such as Kondo effect, Mott transition, and heavy fermion behavior. Here we present a study of the new heavy fermion compound CeAuBi$_{\mathrm{2}}$. This material exhibits spindensitywave antiferromagnetic ordering below 13 K and a magneticfieldtuned quantum critical point. The electronic structure was investigated with Angle Resolved Photoemission Spectroscopy (ARPES), which reveals a low energy spectrum dominated by strongly dispersing metallic bands and localized fstates with weak hybridization effects. By means of resonant ARPES we were able to selectively study the Ce$^{\mathrm{3+}}$ 4f character of the flat bands situated few meV from the Fermi level. The experimental dispersion is compared to abinitio band structure calculations for a microscopic understanding of the electronic structure. [Preview Abstract] 
Monday, March 13, 2017 4:18PM  4:30PM 
C20.00010: Unusual phase boundary and altered Fermi surface in CeOs$_4$Sb$_{12}$ at high magnetic fields PeiChun Ho, John Singleton, Paul A. Goddard, Fedor F. Balakirev, Shalinee Chikara, M. Brian Maple, Tatsuya Yanagisawa The filled skutterudite compounds CeOs$_4$Sb$_{12}$ is a 1K antiferromagnetic (AFM) semimetal and candidate topological insulator. Using magnetization ($M$), MHzconductivity and electrical resistivity ($\rho$) data recorded at magnetic fields of up to $\mu_0 H = 60$ T and temperature $T$ down to 0.4 K, we map out the $(H, T)$ phase diagram. At low $T$ and low $H$ (L phase), the Ce $4f$ electron is delocalized, yielding heavy quasiparticles with a small Fermi surface, while at high $T$ and high $H$ (H phase) the $4f$ electron is quasilocalized, leaving a single, almost spherical Fermi surface of lightmass holes. The behavior of $\rho$ and $dM/dH$ on crossing the LH boundary, plus comparisons with bandstructure calculations, suggest that the LH phase transition in CeOs$_4$Sb$_{12}$ is similar in origin to the $\alpha  \gamma$ transition in Ce and its alloys. However, interplay between the freeenergy contributions of the AFM and L phases results in a very unusual curvature of the phase boundary at low $T$. [Preview Abstract] 
Monday, March 13, 2017 4:30PM  4:42PM 
C20.00011: Effect of controlled point like disorder on lowenergy quasiparticle excitations in CeCu$_2$Si$_2$ Takaaki Takenaka, Yuta Mizukami, Marcin Konczykowski, Silvia Seiro, Hirale S Jeevan, Christoph Geibel, Joe A Wilcox, Carsten Putzke, Antony Carrington, Yoshifumi Tokiwa, Yuji Matsuda, Takasada Shibauchi CeCu$_2$Si$_2$ is a prototypical heavyfermion superconductor found in 1979 with $T_c$ $\sim$ 0.6 K. The gap structure of CeCu$_2$Si$_2$, which is a direct consequence of the pairing mechanism, is believed as line nodal $d$wave type. However, recent lowtemperature specific heat, thermal conductivity and penetration depth measurement in single crystals of CeCu$_2$Si$_2$ demonstrate the absence of gap nodes at the any point on the Fermi surface. Such a fully gapped state may still have a sign change of gap function between separated Fermi surfaces. To test this $s_\pm$ state, we focus on the impurity effect on the lowenergy quasiparticle excitations. If the signreversing state is realized, midgap states due to the interband scattering is created around the Fermi level with increasing disorder and extra lowenergy excitation appears. On contrary to this, in the signpreserving state, no midgap state is formed by disorder. To introduce impurity scattering by homogeneous point defect, we employ 2.5 MeV electron irradiation. Here, we report on systematic measurements of penetration depth $\lambda$ in CeCu$_2$Si$_2$ with increasing the point defect, from which we will discuss the gap symmetry in this system. [Preview Abstract] 
Monday, March 13, 2017 4:42PM  4:54PM 
C20.00012: Investigation of magnetic ordering in the chemical substitution series CeCu$_{\mathrm{2}}$(Si$_{\mathrm{1x}}$P$_{\mathrm{x}})_{\mathrm{2}}$ You Lai, Andrew Gallagher, Liusuo Wu, Andrew Christianson, Ryan Baumbach CeCu$_{\mathrm{2}}$Si$_{\mathrm{2}}$ is an exemplary correlated electron metal that features two domes of unconventional superconductivity in its temperaturepressure phase diagram. The first dome surrounds an antiferromagnetic quantum critical point, whereas the more exotic second dome may span the zero temperature termination point of a line of $f$electron valence transitions. It has been proposed that the second superconducting dome encompasses a quantum phase transition that is associated with a Ce 4$f$electron valence collapse, but this has yet to be established. In order to clarify this question, we recently investigated the chemical substitution series CeCu$_{\mathrm{2}}$(Si$_{\mathrm{1}}_{x}$P$_{x})_{\mathrm{2\thinspace }}$for $x \le $ 0.1, where Si $\to $ P replacement is understood as electronic tuning. Complex magnetism and other interesting behaviors are induced, with three distinct magnetic regimes appearing with increasing $x$. Using elastic neutron scattering, we report an indepth study of the magnetic ordering in the CeCu$_{\mathrm{2}}$(Si$_{\mathrm{1}}_{x}$P$_{x})_{\mathrm{2}}$ series. We discuss the implications of this behavior for understanding the cerium valence, and for stabilizing remarkable behaviors throughout the Ce$T_{\mathrm{2}}X_{\mathrm{2}}$ ($T \quad =$ transition metal and$ X \quad =$ Si, Ge) family of materials. [Preview Abstract] 
Monday, March 13, 2017 4:54PM  5:06PM 
C20.00013: Emergence of local quantum criticality in a heavyfermion quantum phase transition JaeHo Han, KiSeok Kim We investigate a heavyfermion quantum phase transition from a fractionalized Fermiliquid state with a small Fermi surface to a heavyfermion Fermiliquid phase with a large Fermi surface, expected to be relevant for YbRh$_{\mathrm{2}}$Si$_{\mathrm{2}}$ or Ce(Cu,Au)$_{\mathrm{6}}$. Here, the fractionalized Fermiliquid state is described by a spinliquid state of spinons interacting with gauge bosons and a Fermiliquid phase of conduction electrons with a small Fermi surface. Approaching a quantum critical point from the fractionalized Fermiliquid state, spinons are strongly coupled with conduction electrons, giving rise to Fermisurface fluctuations between the small and large Fermi surfaces and described by critical holon excitations. Based on a recently proposed controlled technique, dimensional regularization for a Fermisurface problem (D.Dalidovich and S.S.Lee, Phys. Rev. B 88, 245106(2013)), we perform renormalization group analysis to reveal the nature of this quantum criticality. We find that the spinon Fermi surface becomes flattened and local moments emerge, expected to cause novel physical properties of the quantum critical region. [Preview Abstract] 
Monday, March 13, 2017 5:06PM  5:18PM 
C20.00014: Quantum critical scaling near the antiferromagnetic quantum critical point in CeCu6xPdx Liusuo Wu, L. Poudel, A. F. May, W. L. Nelson, A. Gallagher, Y. Lai, D. E. Graf, T. Besara, T. M. Siegrist, R. Baumbach, G. Ehlers, A. A. Podlesnyak, M. D. Lumsden, D. Mandrus, A. D. Christianson A remarkable behavior of many quantum critical systems is the scaling of physical properties such as the dynamic susceptibility near a quantum critical point (QCP), where Fermi liquid physics usually break down. The quantum critical behavior in the vicinity of a QCP in metallic systems remains an important open question. In particular, a selfconsistent universal scaling of both magnetic susceptibility and the specific heat remains missing for most cases. Recently, we have studied CeCu$_{\mathrm{6x}}$T$_{\mathrm{x}}$ (T$=$Au, Ag, Pd), which is a prototypical heavy fermion material that hosts an antiferromagnetic (AF) QCP. We have investigated the low temperature thermal properties including the specific heat and magnetic susceptibility. We also investigated the spin fluctuation spectrum at both critical doping and within the magnetically ordered phase. A key finding is the spin excitations exhibit a strong Ising character, resulting in the strong suppression of transverse fluctuations. A detailed scaling analysis of the quantum critical behaviors relating the thermodynamic properties to the dynamic susceptibility will be presented. [Preview Abstract] 
Monday, March 13, 2017 5:18PM  5:30PM 
C20.00015: Competing fluctuations near an unconventional quantum critical point CeCu$_{5.8}$Ag$_{0.2}$ L. Poudel, J. M. Lawrence, F. Ronning, L.S. Wu, G. Ehlers, A. F. May, A. A. Podlesnyak, M. D. Lumsden, Y. Qiu, D. Mandrus, A. D. Christianson CeCu$_{6x}$Au$_x$ is a prototype heavy fermion system that hosts a quantum critical point (QCP). The nature of the QCP in CeCu$_{6x}$Au$_x$ is unique among similar Cebased systems and appears to be inconsistent with the conventional approach developed by HertzMillisMoriya (HMM). We study a related system CeCu$_{6x}$Ag$_x$ for a more comprehensive understanding of this unconventional behavior. Our inelastic neutron spectroscopy measurement of the QCP composition CeCu$_{5.8}$Ag$_{0.2}$ shows that the critical behavior of CeCu$_{6x}$Ag$_x$ is similar to that of CeCu$_{6x}$Au$_x$. The measurement also reveals that there are three competing magnetic fluctuations near the QCP, only one of which goes critical at the QCP. The critical part of the fluctuations is more consistent with the conventional HMM model suggesting that the so called unconventional behavior in these systems is the consequence of strongly competing magnetic fluctuations near the QCP. [Preview Abstract] 
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