Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session X48: Frustrated Magnetism: 2D AntiferromagnetsFocus
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Sponsoring Units: GMAG DMP Chair: V. Ovidiu Garlea, Oak Ridge National Lab Room: 395 |
Friday, March 17, 2017 8:00AM - 8:12AM |
X48.00001: Spin dynamics in the triangular-lattice antiferromagnet Cs$_2$CuBr$_4$ S. Zvyagin, E. Schulze, A. Ponomaryov, J. Wosnitza, M. Ozerov, D. Kamenskyi, J. Krzystek, D. Yoshizawa, M. Hagiwara, R. Hu, H. Ryu, C. Petrovic, M. Zhitomirsky We present results of our recent electron spin resonance (ESR) studies of Cs$_2$CuBr$_4$, a spin-1/2 Heisenberg antiferromagnet with a distorted triangular-lattice structure, in magnetic fields up to 50 T. Studying the magnetic excitation spectrum in the magnetically saturated phase ($H_{sat} \sim 30$ T) allowed us to accurately determine exchange parameters of Cs$_2$CuBr$_4$. In addition, we report on the observation of a substantial zero-field gap, $\sim 10$ K, whose origin will be discussed. The peculiarities of the ESR spectrum above and below $H_{sat}$ are described taking into account the effect of the Dzyaloshinskii-Moriya interaction. [Preview Abstract] |
Friday, March 17, 2017 8:12AM - 8:24AM |
X48.00002: The response of a triangular antiferromagnet to anisotropic lattice distortion Dan Sun, Pallavi Kushwaha, Jhuma Sannigrahi, Jack Bartlett, Andrew Mackenzie, Clifford Hicks The ground state of Heisenberg spins interacting antiferromagnetically on a triangular lattice is 120$^{\circ}$ antiferromagnetic order. We probe the effects of anisotropic lattice distortion on this phase using the material PdCrO$_2$, which has highly-conducting Pd sheets that alternate with Mott-insulating CrO$_2$ layers. The Cr spins order into a 120$^{\circ}$ phase at T$_N$ = 39 K. The conductivity of the Pd sheets can be measured to probe magnetic scattering across the transition. In the unstrained lattice, the resistivity has a sharp first-order-like step at T$_N$. This step persists up to uniaxial compression by $\sim 0.3\%$, then splits into two much broader transitions. This feature suggests a rigidity of the 120$^{\circ}$ phase at T $\sim T_N$ against small perturbations, which we discuss in terms of magnetoelastic coupling and fluctuation effects. [Preview Abstract] |
Friday, March 17, 2017 8:24AM - 8:36AM |
X48.00003: Exact ground states for the nearest neighbor quantum XXZ model on the kagome and other lattices with triangular motifs at $J_z/J_{xy}=-1/2$ Hitesh Changlani, Krishna Kumar, Dmitrii Kochkov, Eduardo Fradkin, Bryan Clark We report the existence of a quantum macroscopically degenerate ground state manifold on the nearest neighbor XXZ model on the kagome lattice at the point $J_z/J_{xy}=-1/2$. On many lattices with triangular motifs (including the kagome, sawtooth, icosidodecahedron and Shastry-Sutherland lattice for a certain choice of couplings) this Hamiltonian is found to be frustration-free with exact ground states which correspond to three-colorings of these lattices. Several results also generalize to the case of variable couplings and to other motifs (albeit with possibly more complex Hamiltonians). The degenerate manifold on the kagome lattice corresponds to a "many-body flat band" of interacting hard-core bosons; and for the one boson case our results also explain the well-known non-interacting flat band. On adding realistic perturbations, state selection in this manifold of quantum many-body states is discussed along with the implications for the phase diagram of the kagome lattice antiferromagnet. [Preview Abstract] |
Friday, March 17, 2017 8:36AM - 8:48AM |
X48.00004: Magnetic Properties of New Triangular Lattice Magnets A$_4$B’B$_2$O$_{12}$ Ryan Rawl, Haidong Zhou, Jie Ma, Clarina Dela Cruz, Minseong Lee, Eun Sang Choi, Kuan Wen Chen, Ryan Baumbach Quasi-two dimensional (-2D) triangular lattice magnets (TLMs) may adopt a variety of intriguing ground states including a 120° planar, collinear striped, ferromagnetic, and quantum spin liquid structures. Reduction of interplane interactions can be engineered via addition of non-magnetic layers and provide a glimpse into more truly 2D behavior on a triangular lattice. Members of A$_4$B’B$_2$O$_{12}$ (A=Ba, La, Sr; B’= Co, Ni, Mn) have been synthesized and examined using x-ray diffraction, AC and DC susceptibility, specific heat, and powder neutron diffraction. The magnetic properties are examined in relation to chemical pressure and spin size. A rich phase diagram is observed for Ba$_2$La$_2$MnW$_2$O$_{12}$. [Preview Abstract] |
Friday, March 17, 2017 8:48AM - 9:00AM |
X48.00005: Proximity induced spin density waves observed in PdCrO$_{\mathrm{2}}$ Jinoh Jung, Jong-Mok Ok, Won-Jun Jang, Yeong-Hoon Lee, Sung-Bin Lee, Jun-Sung Kim, Jhinhwan Lee PdCrO$_{\mathrm{2}}$ with delafossite structure has an intriguing three-dimensional spin order in the layered triangular Cr lattices. We performed Spin-polarized scanning tunneling microscopy (SPSTM) study on the two equally possible cleaved surfaces terminated with CrO$_{\mathrm{2}}$ and Pd. On the CrO$_{\mathrm{2}}$-terminated surface where direct tunneling to the Cr verified, we could observe no long range magnetic order. The CrO$_{\mathrm{2}}$-terminated surface missing Pd upper layer has different super exchange interaction compared with the bulk CrO$_{\mathrm{2}}$ state, which can explain the suppression of long range magnetic order. However, on the Pd-terminated surface with irregular hexagonal surface reconstruction, we could observe a signature of spin density waves induced by proximity effect associated with the long range $\surd $3x$\surd $3 magnetic order in the CrO$_{\mathrm{2}}$ layer. [Preview Abstract] |
Friday, March 17, 2017 9:00AM - 9:36AM |
X48.00006: Supersolid-like magnetic states in a mixed honeycomb-triangular lattice system. Invited Speaker: Ovidiu Garlea Field-induced magnetic states that occur in layered triangular antiferromagnets have been of broad interest due to the emergence of new exotic phases, such as topologically ordered states and supersolids. Experimental realization of the supersolid states where spin components break simultaneously the translational and rotational symmetries~remains scarce. In this context, the mixed vanadate$-$carbonate K2Mn3(VO4)2CO3 is a very promising system. This compound contains two types of two-dimensional layers alternately~stacked along the crystallographic c-axis:~ one layer consists of a honeycomb~web structure made of edge sharing MnO6 octahedra, while the other consists of MnO5 trigonal bipyramids linked by [CO3] triangles to form a triangular magnetic lattice. Magnetization and heat capacity measurements~reveal a~complex magnetic phase diagram that includes three phase transition associated with sequential long range magnetic ordering of the different sublattices. The lowest temperature state resembles a supersolid state that was predicted to occur in two-dimensional frustrated magnet with easy axis anisotropy. Such a supersolid phase is defined by a commensurate $\surd $3\texttimes $\surd $3~magnetic superlattice, where two thirds of the spins are canted away from the easy axis direction. Applied magnetic field destabilizes this ordered state and induces a cascade of new exotic magnetic ground states. The nature of these field-induced magnetic states is evaluated by using neutron scattering techniques. [Preview Abstract] |
Friday, March 17, 2017 9:36AM - 9:48AM |
X48.00007: Phase diagram of the Heisenberg model on the decorated honeycomb lattice. Dmitrii Kochkov, Rebecca Flint, Bryan Clark We numerically investigate the phase diagram of quantum Heisenberg model on lattices which interpolate between honeycomb and triangular lattice. We show how the known phase diagrams of the honeycomb and triangular lattices interpolate into each other and examine the robustness of the spin liquid phase on the triangular lattice. Using fidelity analysis we discover a host of new ordered phases in this diagram which do not appear in the triangular and honeycomb phase diagrams separately. For the topological phases, we discuss possible spin liquid classifications based on the analysis of modular matrices and the effects of additional chiral interactions. [Preview Abstract] |
Friday, March 17, 2017 9:48AM - 10:00AM |
X48.00008: Magnetic order in frustrated Kagome-Triangular lattice antiferromagnet NaBa$_{\mathrm{2}}$Mn$_{\mathrm{3}}$F$_{\mathrm{11}}$ Shohei Hayashida, Hajime Ishikawa, Yoshihiko Okamoto, Tsuyoshi Okubo, Zenji Hiroi, Maxim Avdeev, Pascal Manuel, Masato Hagihala, Minoru Soda, Takatsugu Masuda We performed powder neutron diffraction experiments on NaBa$_{\mathrm{2}}$Mn$_{\mathrm{3}}$F$_{\mathrm{11}}$ [1], a model compound of \textit{Kagome-Triangular} lattice where three of six next-nearest neighbor interactions are non-negligible. More than 10 magnetic Bragg peaks are clearly observed below $T \quad =$ 2 K, meaning that the ground state is a magnetically ordered state. From indexing the magnetic Bragg peaks, magnetic propagation vector of \textbf{\textit{q}}$_{\mathrm{0}} \quad =$ (0, 0, 0) and two incommensurate vectors which are close to (1/3, 1/3, 0) are identified. Combination of representation analysis and Rietveld refinement reveals that the propagation vector of \textbf{\textit{q}}$_{\mathrm{0}}$ exhibits the 120º structure in the \textit{ab}-plane. Our calculation of the ground state suggests that the non-negligible magnetic dipolar interaction is responsible for the determined 120º structure in NaBa$_{\mathrm{2}}$Mn$_{\mathrm{3}}$F$_{\mathrm{11}}$. Reference [1] H. Ishikawa \textit{et al}., J. Phys. Soc. Jpn. \textbf{83}, 043703 (2014). [Preview Abstract] |
Friday, March 17, 2017 10:00AM - 10:12AM |
X48.00009: Systematic investigation of structural, transport, magnetic and thermodynamic properties of new hexagonal compound GdPtPb Soham Manni, S. L. Bud'ko, P. C. Canfield We have synthesized in single crystalline form a new hexagonal local moment magnet GdPtPb, in the spirit of searching for geometrically frustrated rare earth magnets. Analysis of high temperature magnetic susceptibility data reveals that the system is far from frustrated with a frustration parameter of ($\Theta$/ $T_N$) 0.2-0.3, much less than one which can be explained from mean field theory (MFT) using a two sub-lattice model. Gd $S$=7/2 local moments order antiferomagnetically below 16 K, possibly having a very unusual magnetic structure for a hexagonal system. This magnetic ordering can be tuned by magnetic field along the plane of the spins including a metamagnetic transition around 20 kOe. We have studied the phase diagram under magnetic field. Basically GdPtPb can serve a good example of "anti-frustration" for MFT as a planar non collinear magnet with hexagonal crystal structure. \paragraph{} This research is funded by the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant GBMF4411 and by U.S. Department of Energy under Contract No. DE-AC02-07CH11358. [Preview Abstract] |
Friday, March 17, 2017 10:12AM - 10:24AM |
X48.00010: Topological Triplon Modes and Bound States in a Shastry-Sutherland Magnet Paul McClarty, Frank Kruger, Tatiana Guidi, Stewart Parker, Keith Refson, Tony Parker, Dharmalingam Prabhakaran, Radu Coldea The twin discoveries of the quantum Hall effect, in the 1980’s, and of topoogical band insulators, in the 2000’s, were landmarks in physics that enriched our view of the electronic properties of solids. In a nutshell, these discoveries have taught us that quantum mechanical wavefunctions in crystalline solids may carry nontrivial topological invariants which have ramifications for the observable physics. One of the side effects of the recent topological insulator revolution has been that such physics is much more widespread than was appreciated ten years ago. For example, while topological insulators were originally studied in the context of electron wavefunctions, recent work has led to proposals of topological insulators in bosonic systems: in photonic crystals, in the vibrational modes of crystals, and in the excitations of ordered magnets. Using inelastic neutron scattering along with theoretical calculations we demonstrate that, in a weak magnetic field, the dimerized quantum magnet SrCu$_2$(BO$_3)_2$ is a bosonic topological insulator with nonzero Chern number in the triplon bands and topologically protected chiral edge excitations. [Preview Abstract] |
Friday, March 17, 2017 10:24AM - 10:36AM |
X48.00011: Electrical Transport on the Shastry-Sutherland Lattice in Ising-type Rare Earth Tetraborides Linda Ye, Takehito Suzuki, Joseph. G. Checkelsky In the presence of a magnetic field, frustrated spin systems may exhibit plateaus at fractional values of their saturation magnetization. Study of the magnetic ordering and excitations at such plateaus are key to understanding the nature of the underlying ground states in these systems. Here we study the magnetization plateaus in metallic rare earth tetraborides RB$_4$ with Ising-type anisotropy ($R$ = Er, Tm) in which $R$ resides on a Shastry-Sutherland lattice. We focus on electrical transport and find that the response reflects scattering of charge carriers with the static and dynamic plateau structure. Modeling of these results is consistent with the expected strong uniaxial anisotropy and provides a framework for the study of plateau states in metallic frustrated systems. \\ References Cited: L. Ye, T. Suzuki, J. G. Checkelsky. Electronic Transport on the Shastry-Sutherland Lattice in Ising-type Rare Earth Tetraborides. arXiv:1606.04003 (2016). [Preview Abstract] |
Friday, March 17, 2017 10:36AM - 10:48AM |
X48.00012: High-field magnetotransport studies in microstructures of Yb$_2$Pt$_2$Pb Toni Helm, Fedor Balakirev, Helge Rosner, Maja Bachmann, Philip Moll Yb$_2$Pt$_2$Pb (YPP) is a strongly frustrated Shastry Sutherland (SSL) Anitiferromagnet with a a ordering temperature of $T{_N} = 2\,$K. The antiferromagnetic (AF) order is comprised of two AF sublattices built from dimers of Yb$^{3+}$ ions in the $ab$ planes [1]. Unlike other quantum magnets, YPP is a highly conductive metal [2]. Recently, exotic quantum effects were reported from neutron scattering experiments that indicate charge-orbital separation along the $c$ axis, similar to quasi-1D materials [3]. To study the influence of YPP’s rich magnetic structure on the anisotropic charge transport, we fabricated micron-sized transport devices from single crystalline YPP by Focused Ion Beam etching. This technique enables high-precision magnetotransport measurements along the most relevant lattice directions in magnetic fields of up to $65\,$T. Our findings reveal insights on the electronic structure of YPP. [1] Miiller, W. et al. PRB 93,104419 (2016) [2] Kim, M.S. and Aronson, M.C. PRL 110, 017201 (2013) [3] Wu, L. S. et al. Science 352,6290pp1206 (2016) [Preview Abstract] |
Friday, March 17, 2017 10:48AM - 11:00AM |
X48.00013: Investigating the Role of Disorder, Electron Concentration, and Lattice Compression on Heaviness of Uranium-based Compounds Eteri Svanidze, Alfred Amon, Andreas Leithe-Jasper, Yuri Grin Uranium intermetallic compounds exhibit a wide range of exotic properties -- unconventional superconductivity and quantum criticality, complex magnetic configurations, as well as heavy fermion and non-Fermi liquid behaviors. And while all of these phenomena are related to the degree of localization of the $5f$ electronic states, the complete understanding of underlying mechanisms is still lacking, explaining the unceasing interest in heavy fermion systems. One of the avenues in the search for heavy fermions has focused on compounds with high coordination number and, therefore, low concentration of U atoms. One such example is given by U$_2$Zn$_{17}$ -- a heavy fermion antiferromagnet which exhibits a Sommerfeld coefficient $\gamma = 0.4$ J/mol K$^2$. In the presented work, the value of $\gamma$ was doubled by substituting all of Zn atoms by Cu and Ga, resulting in U$_2$Cu$_{17-x}$Ga$_x$. Moreover, this drastic effect is accompanied by non-Fermi liquid behavior. We analyze the relation between crystal structure, magnetic, and electronic properties of the U$_2$Cu$_{17-x}$Ga$_x$ compounds. [Preview Abstract] |
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