Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B46: Triangular Lattice IFocus
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Sponsoring Units: GMAG DMP Chair: Alexander Chernyshev, University of California, Irvine Room: 708 |
Monday, March 2, 2020 11:15AM - 11:51AM |
B46.00001: Quantum effect in the antiferromagnetic layered-perovskite materials with the triangular-lattice Invited Speaker: Jie Ma Due to the exotic quantum phenomena of the frustrated quantum magnets, investigating the related ground states has caught a lot of attention. The two-dimensional Spin-1/2 triangular-lattice antiferromagnet (TLAF) is a typical example: the quantum fluctuations could interfere the spin states, such as the disordered liquid and glass phases, and keep them with the complicated interactions among the geometric frustration, low dimensionality, and small spin. Ba3CoSb2O9 is the first spin-1/2 equilateral TLAF without the Dzyaloshinskii-Moriya interaction, and the magnetic Co2+ triangular layers are well separated by the non-magnetic clusters of the Sb2O9 bioctahedra and Ba2+ ions. The strong quantum effects were observed from a non-collinear 120° spin structure in zero magnetic field into a collinear up-up-down (uud) state in a finite range of applied magnetic field [1, 2]. Through the experimental and theoretical studies, we found that the Linear Spin-Wave + 1/S treatment was inadequate to explain our experimental observation and the interlayer interaction could not be ignored in the system [3, 4]. In order to study the interlayer interactions and magnetic moments dependence on the quantum effect, the work has been extended to the other TLAFs of the multi-layered perovskite compounds with S=1 and 5/2. Moreover, the non-magnetic B'-site ions of the AmBB'm-1O3m were discussed. |
Monday, March 2, 2020 11:51AM - 12:03PM |
B46.00002: Effect of quenched disorder on an equilateral triangular lattice antiferromagnet Ba3CoSb2O9 Qing Huang, Haidong Zhou, Tao Hong, Eun Sang Choi, Jie Ma, Lu Li, Cole D Mauws, Christopher Wiebe Ba3CoSb2O9 is one of few prototypical materials for the two-dimensional equilateral triangular lattice antiferromagnet. We present a systematic study on effect of quenched disorder on magnetic properties in the Sr doped single-crystalline sample of Ba2.8Sr0.2CoSb2O9 by means of DC and AC susceptibilities, specific heat and advanced neutron scattering. DC susceptibility in Ba2.8Sr0.2CoSb2O9 confirms an antiferromagnetic ordering below 2.8 K with an easy-plane anisotropy. AC susceptibility as a function of magnetic field measured at 0.02 K indicates a phase transition around 8 T. Evolution of the transition temperature as a function of field was determined by specific heat measurements in Ba2.8Sr0.2CoSb2O9. We will also discuss effect of side disorder on the magnetic structure in Ba2.8Sr0.2CoSb2O9 using the single-crystal neutron diffraction technique. |
Monday, March 2, 2020 12:03PM - 12:15PM |
B46.00003: Universal scaling of the heat capacity in a quantum spin liquid state of 1T-TaS2 Hinako Murayama, Yuki Sato, Tomoya Taniguchi, Ryo Kurihara, Hiroki Suzuki, Xianzhuo Xing, Wenkai Huang, Shigeru Kasahara, Yuichi Kasahara, Itamar Kimchi, Masaro Yoshida, Yoshihiro Iwasa, Marcin Konczykowski, Yuji Matsuda To elucidate the nature of quantum spin liquid (QSL), it is important to understand the effect of randomness on QSL. Here, we have investigated the low energy excitations on pure, Se-substituted and electron-irradiated 1T-TaS2, a QSL candidate material with spin-1/2 on a triangular lattice[1, 2], by measuring low-temperature thermal conductivity and heat capacity. Finite residual linear terms of thermal conductivity, κ/T(T→0), in pure 1T-TaS2 indicates the presence of itinerant gapless excitations. The magnetic contribution of the heat capacity of 1T-TaS2 and 1T-TaS2−xSex well obeys a universal scaling relation, consistent with a theory that assumes the presence of localized orphan spins forming random singlets[3]. These results capture a microscopic picture of the QSL, in which localized orphan spins induced by disorder are surrounded by itinerant spinon that forms Fermi surface. On the other hand, electron irradiation in 1T-TaS2, which introduces strong quenched disorders in Ta-layers, changes the scaling function dramatically, suggesting a possible new state of spin liquid. |
Monday, March 2, 2020 12:15PM - 12:27PM |
B46.00004: Magnetic Excitations and Q-dependent magnon lifetime in Non-collinear Metallic Antiferromagnet CrB2 Pyeongjae Park, Kisoo Park, Taehun Kim, Yusuke Kousaka, Jun Akimitsu, Toby G. Perring, Michel Kenzelmann, Je-Guen Park Frustration and non-collinear magnetic ordering can introduce a wide variety of interesting physics; like a quantum spin liquid phase in insulators or topological band structures in metals, to name a few. Many studies have been made on the nature of magnetic excitations in non-collinear insulating magnets, while few experimental data exist for non-collinear metallic magnets. Using an inelastic neutron scattering technique, we report the magnetic excitation spectra of single crystal CrB2; a metallic magnet in which magnetic moments of Cr on triangular lattice form incommensurate spiral magnetic order with the propagation vector k =(0.285,0.285,0). Severely damped magnons are observed along with clear phonons which are as sharp as the instrumental resolution, yet most of them can be explained by Heisenberg Hamiltonian and a linear spin wave theory (LSWT). By excluding the effects of instrumental resolution, we mapped the intrinsic magnon linewidth Γ(q, E) which shows some unusual behavior. We discuss the origin of the magnon decay by calculating 2-magnon density of states (DOS) and Stoner continuum DOS. Our work will be a rare comprehensive study on the spin dynamics of non-collinear metallic magnets; the 1st observation of 2-magnon effect in metallic magnets. |
Monday, March 2, 2020 12:27PM - 12:39PM |
B46.00005: Terahertz study of the frustrated triangular Ising magnet FeI2 Anaelle Legros, Dipanjan Chaudhuri, Xiaojian Bai, Zhiling Dun, Martin Mourigal, Peter Armitage 2D antiferromagnetic (AF) triangular lattices are of great interest due to their geometric frustration, which may lead to the absence of a long-range magnetic order at T=0. FeI2 is part of the ferrous halides family, in which the Fe2+ ions are distributed on hexagonal planes and spontaneously order in an AF phase below TN∼9K [1]. Contrary to other ferrous halides, the spins in the ordered phase of FeI2 form triangular AF sheets (instead of antiparallel ferromagnetic sheets), giving rise to a more complex magnetic structure. In this peculiar ground state, the spins (S=1) generate several types of magnetic excitations, including a mysterious two-magnon bound state that should be prevented by selection rules [2]. Moreover, when an external magnetic field is applied along the c-axis at T<TN, successive magnetic transitions occur, including a phase without evidence of long-range order [3]. We present the results from in-field time-domain terahertz spectroscopy on FeI2. These experiments give insight into the diverse magnetic excitations of this triangular AF lattice. |
Monday, March 2, 2020 12:39PM - 12:51PM |
B46.00006: Synthesis and frustrated magnetism of the triangular lattice ARESe2 single crystals Jie Xing, Liurukara D Sanjeewa, Jungsoo Kim, Gregory Randall Stewart, Maohua Du, Fernando Reboredo, Radu Custelcean, Athena S. Sefat We have successfully synthesized ARESe2 (A = Alkali metal, RE=rare-earth) single crystals by the salt flux. These crystals stabilize in either the trigonal (R-3m) or hexagonal (P63/mmc) crystal systems depending on the RE, containing the ideal triangular RE3+ layers. We have characterized them through magnetization and heat capacity down to 0.4 K. Antiferromagnetic interactions with large magnetic anisotropy is observed, while no long-range order is found indicating frustrated magnetism. Yb-based crystals present a two-peak feature in the heat capacity below 10 K, while the magnetic plateau is found at 4 T when the magnetic field is applied in the ab plane. The 112 system is found to be particularly interesting for the study of frustrated magnetism and its potential for quantum spin liquid behavior. |
Monday, March 2, 2020 12:51PM - 1:03PM |
B46.00007: Measurement of a 1/2 magnetization plateau in a frustrated antiferromagnet Shannon Haley, Nikola Maksimovic, Eran Maniv, Daniel Parker, John Singleton, Joel Moore, James Analytis Frustrated magnetic systems lend themselves to a wealth of nontrivial behaviors. Among these are plateaus in magnetization with the application of an external field, resulting from quantum fluctuations stabilizing particular spin states. The existence of these plateaus at specific fractions of the saturated magnetization has been observed in a handful of systems with distinct physics. This talk will discuss our recent discovery of a ½ magnetization plateau in a frustrated antiferromagnet on a triangular lattice using fields up to 65T. This directly confirms recent theoretical predictions in frustrated magnets. |
Monday, March 2, 2020 1:03PM - 1:39PM |
B46.00008: Novel Excitations near Quantum Criticality in Geometrically Frustrated Antiferromagnet CsFeCl3 Invited Speaker: Takatsugu Masuda The investigation of materials that exhibit quantum phase transition provides valuable insights into fundamental problems in physics. We present neutron scattering under pressure in a triangular-lattice antiferromagnet that has a quantum disorder in the low-pressure phase and a noncollinear structure in the high-pressure phase [1]. The neutron spectrum continuously evolves through critical pressure; a single mode in the disordered state becomes soft with the pressure and it splits into gapless and gapped modes in the ordered phase. Extended spin-wave theory reveals that the longitudinal and transverse fluctuations of spins are hybridized in the modes because of noncollinearity, and novel magnetic excitations are formed. We report a new hybridization of the phase and amplitude fluctuations of the order parameter near a quantum critical point in a spontaneously symmetry-broken state. |
Monday, March 2, 2020 1:39PM - 1:51PM |
B46.00009: Evidence of one-dimensional magnetic heat transport in the triangular-lattice antiferromagnet Cs2CuCl4 Erik Schulze, Stevan Arsenijevic, Lars Opherden, Alexey Ponomaryov, Joachim Wosnitza, Toshio Ono, Hidekazu Tanaka, Sergei Zvyagin We report on low-temperature heat-transport properties of the spin-1/2 triangular-lattice antiferromagnet Cs2CuCl4. Broad maxima in the thermal conductivity along the three principal axes, observed at about 5 K, are interpreted in terms of the Debye model, including the phonon Umklapp scattering. For thermal transport along the b axis, we found a pronounced field-dependent anomaly, close to the transition into the three-dimensional long-range-ordered state. No such anomalies were observed for the transport along the a and c directions. We argue that this anisotropic behavior is related to an additional heat-transport channel through magnetic excitations, that can best propagate along the direction of the largest exchange interaction. Our observations strongly support the quasi-1D spin-liquid scenario with spinons as elementary excitations, proposed for this frustrated antiferromagnet. Besides, peculiarities of the heat transport of Cs2CuCl4 in magnetic fields up to the saturation field and above are discussed. |
Monday, March 2, 2020 1:51PM - 2:03PM |
B46.00010: Torque equilibrium spin wave theory study of anisotropy and Dzyaloshinskii-Moriya interaction effects on the indirect K− edge RIXS spectrum of a triangular lattice antiferromagnet Trinanjan Datta, Shangjian Jin, Luo Cheng, Dao-Xin Yao We apply the recently formulated torque equilibrium spin wave theory (TESWT) to compute the 1/S-order interacting K -edge bimagnon resonant inelastic x-ray scattering (RIXS) spectra of an anisotropic triangular lattice antiferromagnet with Dzyaloshinskii-Moriya (DM) interaction [1]. We extend the interacting torque equilibrium formalism, incorporating the effects of DM interaction, to appropriately account for the zero-point quantum fluctuation that manifests as the emergence of spin Casimir effect in a noncollinear spin spiral state. Using inelastic neutron scattering data from Cs2CuCl4 we fit the 1/S corrected TESWT dispersion to extract exchange and DM interaction parameters. We compare, and contrast the effects of spatial anisotropy and DM interaction on the RIXS spectra at various points across the magnetic Brillouin zone. We highlight the key features of the bi- and trimagnon RIXS spectrum at the roton like points whose behavior is quite different from an isotropic triangular lattice system [2]. Our calculation offers a practical example of how to calculate interacting RIXS spectra in a non-collinear quantum magnet using TESWT. [1] Jin et. al. Phys. Rev. B 100, 054410 (2019); [2] Luo et. al. Phys. Rev. B 92, 035109 (2015). |
Monday, March 2, 2020 2:03PM - 2:15PM |
B46.00011: A New Yb-based Spin-1/2 Triangular Lattice Magnet Shu Guo, Robert J. Cava Very recently, two rare earth (R)-based triangular lattice (TL) materials, YbMgGaO4 and NaYbO2, are proposed to be quantum spin liquid candidate. From the structural point of view, the magnetic R atoms of these two compounds display a “ABCABC” stacking form in c axis. However, seldom research is focused on the “AA” cubic stacking R-based TL materials. Here, we present a cubic stacking Yb-based TL magnet. The centimeter-size single crystals of Yb-based TL magnet were grown by the flux method. In the crystal structure, the Yb-Yb separation (8.06 angstroms) between layers is larger than the in-plane Yb-Yb separation (5.63 angstroms). The absence of long-range ordering was confirmed by the magnetization (down to 1.8 K). Specific heat measured down to 0.3 K at zero field also confirmed the absence of long-range ordering. For applied field above 3 T, there is still no evidence of long-range magnetic ordering, but instead, a broad peak appears. This broad hump is associated with Schottky anomaly that shifts to higher temperatures at higher fields. |
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