Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B50: Correlated FElectron Materials 
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Sponsoring Units: DCMP Chair: Kaya Wei, Florida State Univ Room: Mile High Ballroom 1C 
Monday, March 2, 2020 11:15AM  11:27AM 
B50.00001: Phase stabilization by electronic entropy in plutonium Neil Harrison, Jonathan B Betts, Mark Wartenbe, Fedor Balakirev, Scott Richmond, Marcelo Jaime, Paul H Tobash Plutonium metal undergoes an anomalously large 25\% collapse in volume from its largest volume $\delta$ phase ($\delta$Pu) to its low temperature $\alpha$ phase, yet the underlying thermodynamic mechanism has largely remained a mystery. Here we use magnetostriction measurements to isolate a previously hidden yet substantial electronic contribution to the entropy of $\delta$Pu, which we show to be crucial for the stabilization of this phase. The entropy originates from two competing instabilities of the $5f$electron shell, which we show to drive the volume of Pu in opposing directions, depending on the temperature and volume. Using calorimetry measurements, we establish a robust thermodynamic connection between the two excitation energies, the atomic volume, and the previously reported excess entropy of $\delta$Pu at elevated temperatures. 
Monday, March 2, 2020 11:27AM  11:39AM 
B50.00002: Physical Properties of 1Dimensional 4f/5felectron Heavy Fermion Materials Eric Bauer, T. Asaba, Sean Thomas, Joe D Thompson, Priscila Rosa, Filip Ronning Quantum criticality has been an organizing principle to explain the behavior of many families of quantum materials including the hightemperature cuprate and ironbased superconductors and felectron heavy fermion compounds. A central, unresolved issue is the effect on the dimensional character of the quantum fluctuations has on the properties of the system. Most work to date has focused on quantum criticality with twodimensional (2D) and threedimensional (3D) fluctuations. Strong quantum fluctuations are expected in quasi1D materials. Furthermore, these 1D systems may be treated exactly by theoretical tools such as Density Matrix Renormalization Group, providing robust and accurate methods for accounting for the strong correlations in 1D felectron materials. In this talk, I will describe the thermodynamic and transport properties of several 4f and 5f quasi1D heavy fermion materials. 
Monday, March 2, 2020 11:39AM  11:51AM 
B50.00003: Probing the local 4forbital symmetry in heavy fermion systems by linearly polarized angleresolved corelevel hard xray photoemission spectroscopy Akira Sekiyama, Hidenori Fujiwara, Satoru Hamamoto, Yuina KanaiNakata, Shin Imada, Arata Tanaka, Kenji Tamasaku, Tetsuya Ishikawa Groundstate (GS) orbital symmetry determined by the local effective crystalline electric fields (CEF) in strongly correlated electron systems play crucial roles in their functional properties such as superconductivity and multipolar ordering. We have found that the CEFsplit GS 4forbital symmetry can be probed by linear dichroism (LD) in angleresolved core dlevel hard xray photoemission owing to the selecion rules in the optical process [1]. We have applied this technique to Ce, Pr, and Ybbased heavy fermion systems, where the Γ_{7} states with Jz = ±3/2 and the Γ_{8} states in the CEFsplit GS 4f symmetry have been established for tetragonal YbRh_{2}Si_{2} [2] and cubic YbB_{12} [3]. Mutually different LDs reflecting the different orbital symmetry have been seen for cubic PrBe_{13}, PrB_{6}, and PrIr_{2}Zn_{20} [4,5]. This technique has also revealed the CEFsplit GS 4f wave functions for a pressureinduced superconductor CeCu_{2}Ge_{2} [6]. 
Monday, March 2, 2020 11:51AM  12:03PM 
B50.00004: Pressure effect on the chiral helimagnetic order in YbNi_{3}Al_{9} Yoshihiko Ota, Kazunori Umeo, Takumi Otaki, Yudai Arai, Takahiro Onimaru, Shota Nakamura, Shigeo Ohara YbNi_{3}Al_{9} crystalizes in the trigonal ErNi_{3}Al_{9}type structure with a space group of R32. This compound undergoes the chiral helimagnetic (CHM) order at T_{M }= 3.4 K. According to the chiral sineGordon model, the CHM order is realized by the competition between the DzyaloshinskiiMoriya interactions and the ferromagnetic (FM) interactions, both of which work along the helical axis. By applying magnetic field perpendicular to the helical caxis, the magnetic phase transition to the forced FM state manifests itself at B_{c} = 0.1 T in association with the divergence of the helical pitch. 
Monday, March 2, 2020 12:03PM  12:15PM 
B50.00005: Quadrupolar fluctuations of heavyfermion metal YbRu_{2}Ge_{2} Mai Ye, Elliott W Rosenberg, Ian Fisher, Girsh Blumberg Longrange order of electric quadrupole moments is one characteristic phenomenon in the family of multipolar Kondo systems. The heavyfermion metal YbRu_{2}Ge_{2} enters a ferroquadrupolar (FQ) phase below T_{FQ}=10K, in which the B_{1g}symmetry quadrupole moments at Yb^{3+} sites order at zero wave vector [Proc. Natl. Acad. Sci. U.S.A. 116, 7232 (2019)]. This FQ phase is a realization of electronic nematic states since the electronic properties spontaneously break the fourfold rotational symmetry of the tetragonal crystal. We study the quadrupolar fluctuations of this compound by Raman scattering [Phys. Rev. B 99, 235104 (2019)]. The electronic Raman susceptibility in quadrupolar symmetry channels exhibit nearly Curielaw behavior, indicating weak exchange interactions between local quadrupoles. It is the relatively strong coupling between the quadrupole moments and the lattice strain fields in the B_{1g} symmetry channel, analogous to cooperative JahnTeller effect, that enhances the vanishingly small Weiss temperature to the temperature of quadrupolar phase transition at T_{FQ}. 
Monday, March 2, 2020 12:15PM  12:27PM 
B50.00006: Thermodynamic and transport properties of Kondo lattice YbCuAs_{2} single crystals Eundeok Mun, David Evans, Symphony Huang YbCuAs_{2} compound crystallizes into a tetragonal ZrCuSi_{2}type structure. Magnetic susceptibility measurements for the YbCuAs_{2} 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 YbCuAs_{2} 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 YbCuAs_{2} single crystals. 
Monday, March 2, 2020 12:27PM  12:39PM 
B50.00007: Dynamical Scaling of Charge Responses at a Kondo Destruction Quantum Critical Point Stefan B. Kirchner, Haoyu Hu, Ang Cai, Zuodong Yu, Qimiao Si An overarching question on quantum criticality is whether and how it goes beyond the Landau framework of orderparameter fluctuations. In the studies of heavy fermion metals, the notion of Kondo destruction has been developed to address this issue [1]. Microscopically, it captures how the interlocalmoment singlet formation dynamically competes with the Kondosinglet formation at the quantum critical point (QCP). An exciting recent surprise is that charge dynamics is also singular and shows omega/T scaling at the prototype antiferromagnetic QCP of YbRh2Si2 [2]. We study prototype models for Kondo destruction QCP, and find that both the charge and spin responses are singular and obey omega/T scaling [3,4]. The criticality of the charge dynamics originates from an felectron delocalizationlocalization across the Kondo destruction QCP. Broader implications of our results are discussed, both for the beyondLandau quantum criticality in general and for the exotic excitations and unconventional superconductivity of strongly correlated metals. 
Monday, March 2, 2020 12:39PM  12:51PM 
B50.00008: Itinerant Nature of Ce in CeCo_{5} Renu Choudhary, Durga Paudyal Due to the high uniaxial anisotropy and abundant nature of Ce, CeCo_{5} has attracted the attention of scientists for developing an excellent permanent magnet. Here, we discuss the itinerant nature of Ce in CeCo_{5} using density functional theory (DFT). Ce based intermetallic compounds show interesting magnetism because of the mixedvalence 4f state. The 3+ valence would have provided 1.0 µ_{B}/Ce 4f; however, in either case with and without employing onsite electron correlation parameter, we obtain 4f spin moment less than 1.0 µ_{B}/Ce 4f. Also, the 3d5d hybridization in CeCo_{5} is strong enough to overlap 4f states below the Fermi level and form a 3d5d4f hybridization thereby indicating the itinerant nature of Ce 4f in CeCo_{5}. This assessment allows us to consider CeCo_{5} as an itinerant magnetic material system suitable to treat by standard DFT. Further, the 4f spin moment of CeCo_{5} is partially canceled by the orbital counterpart and the Co moment is reduced by the stronger 3d4f hybridization in the spindown channel. 
Monday, March 2, 2020 12:51PM  1:03PM 
B50.00009: The ground state and Fermisurface nesting phenomenon in antiferromagnetic CeAuSb_{2}. JAEKYUNG JANG, Joo Yull Rhee Recently, it was reported that, under an external magnetic field (≤ 3T) along the caxis, the inplane wave vector of the spindensity wave (SDW) is (η, η, ½) with η ≈ 0.136 for CeAuSb_{2} compound. To elucidate this SDW and the ground state we investigate the electronic structure of antiferromagnetic (AFM) CeAuSb_{2} using the fullpotential linearizedaugmentedplanewave method. The results of volume optimize calculations and total energy show that 1 x 1 x 2 unit cell construction with ↑↑↓↓ AFM configuration is the ground state, which are well matched with experiments. Fermi surface (FS) on the abplane exhibit FS nesting along the (110) direction. The nesting vector q = (ζ, ζ, ½) (2π/a) with ζ ~ 1/7, is very similar to the results of experiment. To confirm the relation between this FS nesting and SDW we will calculate the generalized susceptibility χ(q). 
Monday, March 2, 2020 1:03PM  1:15PM 
B50.00010: Microscopic Nature of Magnetic Ground State in CeAuSb_{2} George Yumnam, Yiyao Chen, Yang Zhao, A. Thamizhavel, Sudesh K. Dhar, Deepak K Singh The synergistic investigation of groundstate magnetic correlation in the singlecrystal heavyfermion compound CeAuSb_{2} using detailed neutron scattering measurements and density functional calculations is presented. Unlike previous reports of single antiferromagnetic transition at T_{N} = 6K, three successive transitions with distinct critical exponents at T_{N }= 5.3, 4.46, 3.76 K, respectively, are detected in CeAuSb. The lowtemperature groundstate magnetic correlation is described by the spin density wave order in the basal plane with the propagation wave vector (0.135, 0.135, 0.5). The spin density wave order arises due to the nesting of hole pockets in the Fermi surface, with parallel surfaces being separated by the experimentally found propagation vector. The comprehensive investigation of magnetic groundstate properties is expected to provide new insights in understanding the emerging quantum magnetism in this system, including the debated quantum critical state and magnetic fieldinduced metamagnetic transitions at low temperatures. 
Monday, March 2, 2020 1:15PM  1:27PM 
B50.00011: Electronic and Magnetic Properties of EuNi_{2x}Sb_{2} Structural Variants William Nelson, Ashini Jayasinghe, David E Graf, Susan Latturner, Ryan Baumbach XRD, magnetic susceptibility, magnetization, heat capacity, and resistivity results are reported for single crystals of two structural variants of EuNi_{2x}Sb_{2}. While the CaBe_{2}Ge_{2}type structure forms with a stoichiometric ratio, the ThCr_{2}Si_{2}type structure exhibits a Ni site vacancy of 18%. Both systems show CurieWeiss temperature dependence at elevated temperatures, indicating an antiferromagnetic exchange interaction between the Eu^{2+} ions. At low temperatures, the different structural environments give rise to distinct ordering behavior. The CaBe_{2}Ge_{2}variant first orders antiferromagnetically near T_{N2}=6.9K and then undergoes a first order transition at T_{3}=4.6K. The ThCr_{2}Si_{2}variant orders antiferromagnetically at T_{N1}=5.6K. The 4f entropy recovered by the antiferromagnetic ordering is consistent with the predicted J=7/2 Hund's rule multiplet values for the ThCr_{2}Si_{2}variant, while it is reduced for the CaBe_{2}Ge_{2}variant. Thus, EuNi_{2x}Sb_{2} emerges as a useful system in which to study the impact of structural variation on electronic correlations. 
Monday, March 2, 2020 1:27PM  1:39PM 
B50.00012: Magneticallyenhanced lattice instability in EuRh_{2}Si_{2} under pressure Anjana Krishnadas, Stephen Armstrong, Wenli Bi, jiyong zhao, Esen Alp, Riki Kobayashi, Masato Hedo, Takao Nakama, Yoshichika Onuki, Thomas F Rosenbaum, Yejun Feng The family of ThCr_{2}Si_{2} structured rareearth Eu intermetallics exhibits the coexistence of three different instabilities: the competing Kondo and RKKY exchange interactions in heavyfermion magnetic materials, as well as an isostructural collapse of the lattice particular to this type of tetragonal structure. Moreover, there is a valence instability in Eu that connects the lattice and magnetic instabilities, as the Eu^{3+} magnetic moment can vanish with an atomic volume reduction to a nonmagnetic Eu^{2+} state. Here, in a series of ThCr_{2}Si_{2} structured Eu antiferromagnets, we explore the subtle interaction and cooperation between these instabilities under pressure, using synchrotronbased Mossbauer spectroscopy and optical Raman scattering to track the evolution of the magnetism and the lattice, respectively. Exemplified by two end members of this series, we observe that magnetism disappears in EuRh_{2}Si_{2} by 1 GPa, while it persists in EuGa_{4} to beyond 36 GPa at T = 4 K. With the assistance of the magnetic instability, the structural instability in EuRh_{2}Si_{2} demonstrates a pressure dependence of its phase line dT_{s}/dP nearly 100 times higher than that in EuGa_{4}. This dramatic contrast in behavior with applied pressure illuminates a cooperative, magneticallyenhanced structural instability. 
Monday, March 2, 2020 1:39PM  1:51PM 
B50.00013: Magnetic fluctuations in the itinerant ferromagnet LaCrGe3 studied by 139La NMR Khusboo Rana, Hisashi Kotegawa, Rahim R. Ullah, Jeffrey S. Harvey, Sergey L. Bud'ko, Paul C Canfield, Hideki Tou, Valentin Taufour, Yuji Furukawa Recently much attention has been paid to itinerant ferromagnetic (FM) compounds because of the observations of unconventional superconductivity (SC) as well as the avoidance of FM quantum critical point (QCP) under application of pressure (p) and magnetic field (H). In this context, the itinerant ferromagnet LaCrGe3 (Curie temperature of T_{C}=85 K) is very unique. It exhibits an avoided FM QCP under pressure through both a modulated antiferromagnetic phase as well as tricritical wing structure in its temperaturepressuremagnetic field (T−p−H) phase diagram. In order to characterize the static and dynamical magnetic properties of this peculiar material, we carried out ^{139}La nuclear magnetic resonance (NMR) measurements. Here we present our analysis of the NMR data using selfconsistentrenormalization theory and provide a comparison of this system in the generalized RhodesWohlfarth plot with other similar itinerant ferromagnets. 
Monday, March 2, 2020 1:51PM  2:03PM 
B50.00014: Crystal field splitting and spin Hamiltonian of the quantum magnet YbCl_{3} Gabriele Sala, Matthew Stone, Binod Rai, Seunghwan Do, Andrew May, David Parker, Gabor Halasz, Pontus Laurell, Satoshi Okamoto, Nicholas Butch, Yongqiang Cheng, G. Ehlers, Vasile O Garlea, Qiang Zhang, Ganesh Pokharel, Hasitha Suriya Arachchige, David Mandrus, Mark D Lumsden, Andy Christianson YbCl_{3} is a nearly ideal honeycomb lattice quantum magnet. Here we study YbCl_{3} with neutron scattering, magnetic susceptibility, and heat capacity measurements. We determine the crystal field Hamiltonian through simultaneous refinements of the inelastic neutron scattering and magnetization data. The ground state doublet of the crystal field Hamiltonian is well isolated and results in an effective spin1/2 system with local easy plane anisotropy at low temperature. Cold neutron spectroscopy shows low energy spin waves peaked at 0.5 meV that can be understood through a Heisenberg model with a single nearest neighbor exchange interaction. 

B50.00015: Quasi1D Kondo chain in CeCo_{2}Ga_{8} Yongkang Luo “Dimensions are critical”. This is because lower dimension means more phase space for longwavelength fluctuations and a larger magnetic frustration parameter, the latter of which dictates the way that the system undergoes from a quantum ordered state to a disordered state: a conventional spindensitywave (SDW) type quantum critical point (QCP) or an unconventional Kondodestruction type QCP. Kondo destruction generically requires large spin fluctuations and thus favors lower dimension. In a limit where the Kondo coherence is realized in one dimension but fails in others, the Kondo lattice is reduced to a Kondo chain. Our recent study on the CeCo_{2}Ga_{8} manifest that this compound is quasi1D both electrically and magnetically, and most importantly, the Kondo scattering become coherent in caxis but remains incoherent in both a and baxes. The anisotropy scattering mechanism and transport entropy are also investigated by thermopower and Nernst effect measurements. 
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