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Hard Condensed Matter As of July 10, 2020 American Conference on Neutron Scattering Hard Condensed Matter * Invited Paper SESSION B02.01: Magnetic symmetries are tuned. Interaction in Rare Earth Magnets [1] Paddison, Joseph AM, Marcus Daum, Zhiling Dun, Georg Ehlers, Yaohua Liu, Matthew B. Stone, Haidong Zhou, and Martin Mourigal. "Continuous excitations of the triangular-lattice quantum spin B02.01.01* liquid YbMgGaO 4." Nature Physics 13, no. 2 Quantum Disorder and Unconventional (2017): 117-122. Magnetism in ARO2 (A=Alkali Metal, R=Rare [2] Bordelon, Mitchell M., Eric Kenney, Chunxiao Earth Metal) Liu, Tom Hogan, Lorenzo Posthuma, Marzieh Stephen D. Wilson; University of California, Santa Kavand, Yuanqi Lyu et al. "Field-tunable quantum Barbara, United States disordered ground state in the triangular-lattice antiferromagnet NaYbO 2." Nature Physics 15, no. Triangular lattice compounds decorated with 10 (2019): 1058-1064. anisotropic Jeff=1/2 moments have received [3] Rawl, R., L. Ge, H. Agrawal, Y. Kamiya, CR revitalized interest due to experimental reports of Dela Cruz, Nicholas P. Butch, X. F. Sun et al. "Ba 8 quantum disordered ground states in classes of CoNb 6 O 24: A spin-1/2 triangular-lattice layered materials such as YbMgGaO4 [1], Heisenberg antiferromagnet in the two-dimensional NaYbO2 [2], Ba8CoNb6O24 [3] and other related limit." Physical Review B 95, no. 6 (2017): 060412. compounds. Among these, a series of Yb-based compounds of the form NaYbX2 (X=O, S, Se) have B02.01.02 emerged as structurally ideal platforms A Novel Strongly Spin-Orbit Coupled Quantum featuring Jeff=1/2 Yb moments that derive from well- Dimer Magnet—Yb2Si2O7 1 1 isolated Kramers crystal-field doublets. A broad Gavin L. Hester , Harikrishnan S. Nair , Timothy R. 1 1 1 spectrum of these systems fail to establish static Reeder , Danielle Yahne , Tim DeLazzer , Leo 2 2 1 magnetic order, despite an enhanced exchange field Berges , Djamel Ziat , James R. Neilson , Adam 3 3 2 due to relatively close Yb-Yb distances. Uniquely, Aczel , Gabriele Sala , Jeff Quilliam and Kate 1,4 1 these materials can also be driven into an Ross ; Colorado State University, United 2 3 intermediate, fluctuation-driven antiferromagnetic States; Université de Sherbrooke, Canada; Oak state under modest, accessible magnetic fields. This Ridge National Laboratory, United States; 4 opens the phase boundary between native quantum CIFAR, Canada disorder and fluctuation-driven order to experimental exploration with neutron scattering and other The quantum dimer magnet (QDM) is the canonical techniques. In this talk, I will present our work in example of quantum magnetism. The QDM state NaYbO2 exploring the magnetic ground state as well consists of entangled nearest-neighbor spin dimers as its evolution into a collinear up-up-down state and often exhibits a field-induced triplon Bose- under applied magnetic field. I will also discuss some Einstein condensate (BEC) phase. Many compounds 2+ 2+ our recent work studying related ARO2 compounds based on 3d magnetic cations (Cu , Ni ) have been with alternative R-site species and structure-types. found that exhibit a quantum dimer state with a BEC The goal will be to illustrate the spectrum of phase. Due to the energy scales of 3d magnetism, the unconventional magnetic states realized across this critical fields of previous QDM systems with a BEC class of materials as the R-site cation and lattice phase are often above the common field capabilities at neutron sources ( 15 T). We have found a new CePd3 and which can be attributed to particle-hole QDM in the strongly spin-orbit coupled, distorted excitations in a coherent itinerant 4f correlated honeycomb lattice material∼ Yb2Si2O7 which exhibits ground state. The Q-dependence disappears as the a “dome” of field-induced magnetic ordering in the temperature is raised and the 4f electron bandstates field vs. temperature phase diagram, reminiscent of a become increasingly incoherent. The measured BEC phase, with exceptionally low critical fields of phonons can be described adequately by a calculation Hc1 0.4 and Hc2 1.4 T. Our single crystal neutron based on standard band theory, without recourse to scattering, specific heat, and ultrasound velocity 4f correlations. A low temperature magnetic peak at ~ measurements∼ reveal∼ a gapped singlet ground state at 30meV shows dispersion identical to an optic phonon zero field with sharp, dispersive excitations and an branch. This 4f/phonon resonance disappears as the absence of magnetic ordering. Using inelastic neutron temperature is raised. The phonons appear to remain scattering in an applied magnetic field we observe a unaffected by the resonance. We speculate that this Goldstone mode (gapless to within 0.037 meV) that unusual excitation arises from the large amplitude persists throughout the entire field induced beating of the light Al atoms against the heavy Yb magnetically ordered phase, suggestive of the atoms, resulting in an oscillation of the spontaneous breaking of U(1) symmetry expected for 4f/3p hybridization that underlies the heavy fermion a triplon BEC. However, in contrast to other well- physics. known cases of this phase, the high-field (μ0H ≥ 1.2 T) part of the phase diagram in Yb2Si2O7 is B02.01.04 interrupted by an unusual regime signaled by a Crystal Field Splitting and Spin Hamiltonian of change in the field dependence of the ultrasound the Quantum Magnet YbCl3 velocity and magnetization, as well as the Gabriele Sala1, Matthew Stone1, Binod Rai1, Andrew disappearance of a sharp anomaly in the specific heat. May1, David Parker1, Gabor Halasz1, Pontus Laurell1, Inelastic neutron scattering data obtained in the high- Nicholas Butch2, Yongqiang Cheng1, Georg Ehlers1, 1 1 3 field regime (μ0H = 3 T) was fit using linear spin Ovidiu Garlea , Qiang Zhang , Ganesh Pokharel , wave theory as implemented by the Matlab package, Hasitha Suria Arachchige3, David Mandrus3, Mark L. SpinW. Contrary to the expectations for a highly Lumsden1 and Andrew D. Christianson1; 1Oak Ridge spin-orbit coupled compound, the fit indicates that National Laboratory, United States; 2National Yb2Si2O7 exhibits predominantly isotropic Institute of Standards and Technology, United 3 (Heisenberg) exchange. This adds Yb2Si2O7 to the States; The University of Tennessee, Knoxville, growing roster of Yb-based compounds that exhibit United States dominant Heisenberg exchange. Our measurements provide the opportunity to further study how YbCl3 is a nearly ideal honeycomb lattice quantum predominantly isotropic exchange develops in a magnet. We have studied YbCl3 with a combination strongly spin-orbit coupled system and to bring the of neutron scattering, magnetic susceptibility, and full power of neutron scattering to bear on the entire heat capacity measurements. We determine the phase diagram of a BEC compound. crystal field Hamiltonian through simultaneous refinements of the inelastic neutron scattering and B02.01.03 magnetization data. The ground state doublet of the Q-Dependent Kondo Spin Fluctuations and a crystal field Hamiltonian is well isolated and results 4f/Phonon Resonance in the Intermediate Valent in an effective spin-1/2 system with local easy plane Compound YbAl3 anisotropy at low temperature. The low energy Jon Lawrence1,2, Andrew D. Christianson3, Victor excitation spectrum reflecting the collective 3 3 4 1 Fanelli , Lucas Lindsay and Sai Mu ; University of properties of YbCl3 shows strong quantum effects California, Irvine, United States; 2Los Alamos which can be explained by a spin wave theory on an National Laboratory, United States; 3Oak Ridge ideal honeycomb lattice. In particular, we are able to National Laboratory, United States; 4University of identify and explain a novel sharp multimagnon California, Santa Barbara, United States feature occurring atop the multimagnon continuum. The intermediate valence (IV) compound B02.01.05 14- YbAl3 exhibits nonintegral valence (Yb 4f Magnetic Short-Range Correlations and n z f(5d6s) where z = 2+nf = 2.75) in a moderately Continuous Transitions in TmMgGaO4 1 1 2 heavy (m* ~ 20-30me) ground state with a large Zhiling Dun , Marcus Daum , Huibo Cao , Henry 3 2 4 Kondo temperature (TK ~ 600K). We have measured Fischer , Yaohua Liu , Haidong Zhou , Benjamin a single crystal of this material on the ARCS Frandsen5 and Martin Mourigal1; 1Georgia Institute spectrometer at the Spallation Neutron Source. We of Technology, Georgia; 2Oak Ridge National find that at low temperature, the Kondo-scale spin Laboratory, United States; fluctuations have a momentum (Q) dependence 3Institut Laue-Langevin, France; 4The University of similar to that seen recently in the IV compound Tennessee, Knoxville, United States; 5Brigham Young University, United States the paramagnetic phase. I proceed by simulating diffraction data for a range of bond-dependent The rare-earth triangular antiferromagnet models (test cases) on triangular and honeycomb RMgGaO4 is an exciting platform for quantum lattices [8]. I show that simulated paramagnetic magnet studies. For R = Yb, experiments have neutron-diffraction data contain distinctive signatures evidenced a spin-liquid-like behavior at low of the signs of bond-dependent interactions, which temperature whose origin is still under debate. For can therefore be “read” directly from the data. I R=Tm, the system is a promising candidate to realize further demonstrate that, in every test case, values of transverse Ising model based on non-Kramers the bond-dependent interactions can be accurately Tm3+ ion and an effective
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