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 F-Electron 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 1-Dimensional 4f/5f-electron 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 high-temperature cuprate and iron-based superconductors and f-electron 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 two-dimensional (2-D) and three-dimensional (3-D) fluctuations. Strong quantum fluctuations are expected in quasi-1-D materials. Furthermore, these 1-D 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 1-D f-electron materials. In this talk, I will describe the thermodynamic and transport properties of several 4f and 5f quasi-1D heavy fermion materials. |
Monday, March 2, 2020 11:39AM - 11:51AM |
B50.00003: Probing the local 4f-orbital symmetry in heavy fermion systems by linearly polarized angle-resolved core-level hard x-ray photoemission spectroscopy Akira Sekiyama, Hidenori Fujiwara, Satoru Hamamoto, Yuina Kanai-Nakata, Shin Imada, Arata Tanaka, Kenji Tamasaku, Tetsuya Ishikawa Ground-state (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 CEF-split GS 4f-orbital symmetry can be probed by linear dichroism (LD) in angle-resolved core d-level hard x-ray photoemission owing to the selecion rules in the optical process [1]. We have applied this technique to Ce, Pr, and Yb-based heavy fermion systems, where the Γ7 states with Jz = ±3/2 and the Γ8 states in the CEF-split GS 4f symmetry have been established for tetragonal YbRh2Si2 [2] and cubic YbB12 [3]. Mutually different LDs reflecting the different orbital symmetry have been seen for cubic PrBe13, PrB6, and PrIr2Zn20 [4,5]. This technique has also revealed the CEF-split GS 4f wave functions for a pressure-induced superconductor CeCu2Ge2 [6]. |
Monday, March 2, 2020 11:51AM - 12:03PM |
B50.00004: Pressure effect on the chiral helimagnetic order in YbNi3Al9 Yoshihiko Ota, Kazunori Umeo, Takumi Otaki, Yudai Arai, Takahiro Onimaru, Shota Nakamura, Shigeo Ohara YbNi3Al9 crystalizes in the trigonal ErNi3Al9-type structure with a space group of R32. This compound undergoes the chiral helimagnetic (CHM) order at TM = 3.4 K. According to the chiral sine-Gordon model, the CHM order is realized by the competition between the Dzyaloshinskii-Moriya interactions and the ferromagnetic (FM) interactions, both of which work along the helical axis. By applying magnetic field perpendicular to the helical c-axis, the magnetic phase transition to the forced FM state manifests itself at Bc = 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 heavy-fermion metal YbRu2Ge2 Mai Ye, Elliott W Rosenberg, Ian Fisher, Girsh Blumberg Long-range order of electric quadrupole moments is one characteristic phenomenon in the family of multipolar Kondo systems. The heavy-fermion metal YbRu2Ge2 enters a ferro-quadrupolar (FQ) phase below TFQ=10K, in which the B1g-symmetry quadrupole moments at Yb3+ 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 four-fold 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 Curie-law 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 B1g symmetry channel, analogous to cooperative Jahn-Teller effect, that enhances the vanishingly small Weiss temperature to the temperature of quadrupolar phase transition at TFQ. |
Monday, March 2, 2020 12:15PM - 12:27PM |
B50.00006: Thermodynamic and transport properties of Kondo lattice YbCuAs2 single crystals Eundeok Mun, David Evans, Symphony Huang 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 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 order-parameter 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 inter-local-moment singlet formation dynamically competes with the Kondo-singlet 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 f-electron delocalization-localization across the Kondo destruction QCP. Broader implications of our results are discussed, both for the beyond-Landau 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 CeCo5 Renu Choudhary, Durga Paudyal Due to the high uniaxial anisotropy and abundant nature of Ce, CeCo5 has attracted the attention of scientists for developing an excellent permanent magnet. Here, we discuss the itinerant nature of Ce in CeCo5 using density functional theory (DFT). Ce based intermetallic compounds show interesting magnetism because of the mixed-valence 4f state. The 3+ valence would have provided 1.0 µB/Ce 4f; however, in either case with and without employing on-site electron correlation parameter, we obtain 4f spin moment less than 1.0 µB/Ce 4f. Also, the 3d-5d hybridization in CeCo5 is strong enough to overlap 4f states below the Fermi level and form a 3d-5d-4f hybridization thereby indicating the itinerant nature of Ce 4f in CeCo5. This assessment allows us to consider CeCo5 as an itinerant magnetic material system suitable to treat by standard DFT. Further, the 4f spin moment of CeCo5 is partially canceled by the orbital counterpart and the Co moment is reduced by the stronger 3d-4f hybridization in the spin-down channel. |
Monday, March 2, 2020 12:51PM - 1:03PM |
B50.00009: The ground state and Fermi-surface nesting phenomenon in antiferromagnetic CeAuSb2. JAEKYUNG JANG, Joo Yull Rhee Recently, it was reported that, under an external magnetic field (≤ 3T) along the c-axis, the in-plane wave vector of the spin-density wave (SDW) is (η, η, ½) with η ≈ 0.136 for CeAuSb2 compound. To elucidate this SDW and the ground state we investigate the electronic structure of antiferromagnetic (AFM) CeAuSb2 using the full-potential linearized-augmented-plane-wave 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 ab-plane 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 CeAuSb2 George Yumnam, Yiyao Chen, Yang Zhao, A. Thamizhavel, Sudesh K. Dhar, Deepak K Singh The synergistic investigation of ground-state magnetic correlation in the single-crystal heavy-fermion compound CeAuSb2 using detailed neutron scattering measurements and density functional calculations is presented. Unlike previous reports of single antiferromagnetic transition at TN = 6K, three successive transitions with distinct critical exponents at TN = 5.3, 4.46, 3.76 K, respectively, are detected in CeAuSb. The low-temperature ground-state 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 ground-state properties is expected to provide new insights in understanding the emerging quantum magnetism in this system, including the debated quantum critical state and magnetic field-induced metamagnetic transitions at low temperatures. |
Monday, March 2, 2020 1:15PM - 1:27PM |
B50.00011: Electronic and Magnetic Properties of EuNi2-xSb2 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 EuNi2-xSb2. While the CaBe2Ge2-type structure forms with a stoichiometric ratio, the ThCr2Si2-type structure exhibits a Ni site vacancy of 18%. Both systems show Curie-Weiss temperature dependence at elevated temperatures, indicating an antiferromagnetic exchange interaction between the Eu2+ ions. At low temperatures, the different structural environments give rise to distinct ordering behavior. The CaBe2Ge2-variant first orders antiferromagnetically near TN2=6.9K and then undergoes a first order transition at T3=4.6K. The ThCr2Si2-variant orders antiferromagnetically at TN1=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 ThCr2Si2-variant, while it is reduced for the CaBe2Ge2-variant. Thus, EuNi2-xSb2 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: Magnetically-enhanced lattice instability in EuRh2Si2 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 ThCr2Si2 structured rare-earth Eu intermetallics exhibits the coexistence of three different instabilities: the competing Kondo and RKKY exchange interactions in heavy-fermion 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 Eu3+ magnetic moment can vanish with an atomic volume reduction to a non-magnetic Eu2+ state. Here, in a series of ThCr2Si2 structured Eu antiferromagnets, we explore the subtle interaction and cooperation between these instabilities under pressure, using synchrotron-based 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 EuRh2Si2 by 1 GPa, while it persists in EuGa4 to beyond 36 GPa at T = 4 K. With the assistance of the magnetic instability, the structural instability in EuRh2Si2 demonstrates a pressure dependence of its phase line dTs/dP nearly 100 times higher than that in EuGa4. This dramatic contrast in behavior with applied pressure illuminates a cooperative, magnetically-enhanced 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 TC=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 temperature-pressure-magnetic field (T−p−H) phase diagram. In order to characterize the static and dynamical magnetic properties of this peculiar material, we carried out 139La nuclear magnetic resonance (NMR) measurements. Here we present our analysis of the NMR data using self-consistent-renormalization theory and provide a comparison of this system in the generalized Rhodes-Wohlfarth 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 YbCl3 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 YbCl3 is a nearly ideal honeycomb lattice quantum magnet. Here we study YbCl3 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 spin-1/2 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. |
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B50.00015: Quasi-1D Kondo chain in CeCo2Ga8 Yongkang Luo “Dimensions are critical”. This is because lower dimension means more phase space for long-wavelength 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 spin-density-wave (SDW) type quantum critical point (QCP) or an unconventional Kondo-destruction 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 CeCo2Ga8 manifest that this compound is quasi-1D both electrically and magnetically, and most importantly, the Kondo scattering become coherent in c-axis but remains incoherent in both a- and b-axes. The anisotropy scattering mechanism and transport entropy are also investigated by thermopower and Nernst effect measurements. |
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