Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session X39: Triangular Systems IFocus Live
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Sponsoring Units: GMAG DMP Chair: Sara Haravifard, Duke University |
Friday, March 19, 2021 8:00AM - 8:36AM Live |
X39.00001: Anisotropic-exchange magnets: triangular and other cases Invited Speaker: Alexander Chernyshev I will describe our efforts to understand the phase diagram of a model that combines paradigmatic geometrical frustration of spins on a triangular lattice with strong spin-orbit-induced interactions. This model is relevant to a growing family of rare-earth-based magnets and other related materials and our work sets up a consistent interpretation of the current and future experiments in them. I will also review our recent incursion to the honeycomb-lattice territory and attempt to shed light on the properties of the Kitaev materials such as α-RuCl3. |
Friday, March 19, 2021 8:36AM - 8:48AM Live |
X39.00002: Constraining the parameter space of triangular lattice compound YbZnGaO4 William Steinhardt, Sachith Dissanayake, Pavel Maksimov, Zhenzhong Shi, Raju Baral, Nicholas Butch, David E Graf, Andrey Podlesnyak, Yaohua Liu, Joerg Neuefeind, Yang Zhao, Guangyong Xu, Jeffrey W Lynn, Casey Marjerrison, Benjamin Frandsen, Alexander Chernyshev, Sara Haravifard In the last few years Yb- based triangular lattice antiferromagnets emerged as promising quantum spin liquid candidates, and subsequently their ground states have been the subject of ardent debates. Though many experimental and theoretical studies have been devoted to investigating the magnetic properties of these systems at very low temperatures, and exploring a range of possible explanations for the observed spin liquid-like phenomena, a definitive description remains elusive mainly due to chemical disorder. In this talk we discuss further advances in determining the parameter space of YbZnGaO4, using a wide range of experimental techniques and comparisons to theory. |
Friday, March 19, 2021 8:48AM - 9:00AM Live |
X39.00003: Neutron scattering investigation of proposed Kosterlitz-Thouless transitions in the triangular-lattice Ising antiferromagnet TmMgGaO4 Zhiling Dun, Marcus J Daum, Raju Baral, Henry Edward Fischer, Huibo Cao, Yaohua Liu, Matthew Brandon Stone, Jose A. Rodriguez-Rivera, Eun Sang Choi, Qing Huang, Haidong Zhou, Martin P Mourigal, Benjamin Frandsen The transverse-field Ising model on the triangular lattice is expected to host an intermediate Kosterlitz-Thouless (KT) phase through a mapping from spins to a complex order parameter residing on each triangular unit. TmMgGaO4 is a candidate material to realize such physics due to the non-Kramers nature of the Tm3+ ion and two-singlet single-ion ground state. Using inelastic neutron scattering, we confirm this picture by determining the leading parameters of the low-energy effective Hamiltonian. Subsequently, we track the predicted KT phase by inspecting the field and temperature dependence of the ac susceptibility, and spin correlations in both reciprocal space and real space via single-crystal neutron diffraction and magnetic total scattering techniques, respectively. Around 4 K, magnetic pair distribution function analysis provides evidence for the vortex anti-vortex pairs that characterize the proposed Kosterlitz-Thouless phase. Although structural disorder plays a significant role in the field-induced behavior of TmMgGaO4, the magnetism in zero-field appears relatively free from these effects. TmMgGaO4 is thus a rare example of a dense spin system for which continuous phase transitions can be investigated and controlled. |
Friday, March 19, 2021 9:00AM - 9:12AM Live |
X39.00004: The investigation of frustrated magnetism in the triangular lattice ARESe2 single crystals Jie Xing, Liurukara D Sanjeewa, Keith Taddei, Randy Fishman, Marcus J Daum, Martin P Mourigal, Jungsoo Kim, Gregory Randall Stewart, Mao-Hua Du, Fernando A Reboredo, Clarina Dela Cruz, David Parker, Brian Craig Sales, Athena S. Sefat A large class of compounds with the formula of AREQ2 (A = Alkali metal, RE= rare earth, Q = O, S, Se) has been proposed as a good platform for investigating frustrated magnetic ground states[1-3]. The rare earth ions construct the ideal triangular layers, which are separated by A ions. We successfully synthesized ARESe2 single crystals by the salt flux and performed magnetization, heat capacity, and neutron diffraction measurement down to 0.05 K. Antiferromagnetic interaction with large magnetic anisotropy was observed in this system. Yb based compounds present possible QSL ground state at low field. The stripe AFM ground state is found in KErSe2 from the neutron diffraction. All these results reveal this family is an interesting system for the study of frustrated magnetism with rare earth ions. |
Friday, March 19, 2021 9:12AM - 9:24AM Live |
X39.00005: Crystal Growth and Characterization of Tb-Based Triangular Lattice Borate Matthew Ennis, Rabindranath Bag, Sachith Dissanayake, Zhenzhong Shi, Alexander Kolesnikov, Nicholas Butch, Guangyong Xu, Craig Brown, Sara Haravifard Recently, triangular lattice antiferromagnetic materials have attracted attention because competing interactions on the lattice can give rise to exotic phenomena, such as quantum spin liquids. We have initiated systematic efforts to synthesize single crystal samples of a family of rare-earth based triangular lattice antiferromagnet borates. We have performed xray/neutron diffraction, magnetometry, and heat capacity techniques to characterize these compounds. Additionally we have carried out neutron scattering experiments to probe the static and dynamic properties of this family of geometrically frustrated compounds. In this talk, we will present the latest results of our experimental efforts obtained for Tb-based triangular lattice compound, Ba3Tb(BO3)3. |
Friday, March 19, 2021 9:24AM - 9:36AM Live |
X39.00006: Avoided quasiparticle decay and highly-structured excitation continuum in the spin-1/2 near-Heisenberg triangular antiferromagnet Ba3CoSb2O9 David Macdougal, Stephanie Williams, Dharmalingam Prabhakaran, Robert Bewley, David J Voneshen, Radu Coldea We report single-crystal time-of-flight inelastic neutron scattering measurements of the magnetic excitations in the pseudospin-1/2 triangular-lattice near-Heisenberg antiferromagnet Ba3CoSb2O9. We observe sharp magnons throughout reciprocal space with strongly renormalized dispersions and multiple soft modes compared to a linear spin-wave dispersion. At higher energies there is a relatively very strong and highly-structured continuum of excitations with overall weight and intensity modulations in energy and momentum that cannot be captured by a two magnon linear spin-wave cross-section. We attribute the strong dispersion renormalizations that lead to avoided magnon decays and large transfer of spectral weight from magnons to continuum states to the effect of quantum fluctuations and interactions beyond the spin wave approximation. Phys. Rev. B 102, 064421 (2020) |
Friday, March 19, 2021 9:36AM - 9:48AM Live |
X39.00007: Evolution of magnetic-field-induced magnetic ordering in the layered structure quantum Heisenberg triangular-lattice antiferromagnet Ba3CoSb2O9 Nathanael Fortune, Qing Huang, Tao Hong, Yasumasa Takano, Scott Hannahs, Eun Sang Choi, Jie Ma, Zhiying Zhao, N. Li, Haidong Zhou Quantum fluctuations in the effective spin-1/2 layered-structure triangular-lattice quantum Heisenberg antiferromagnet Ba3CoSb2O9 lift the classical degeneracy of the antiferromagnetic ground state in magnetic field, producing a series of novel magnetic-field-induced spin structures. We have used specific heat, neutron diffraction, thermal conductivity, and magnetic torque measurements to map out the phase diagram of this system as a function of magnetic field intensity and orientation relative to the crystallographic ab plane. We report previously unobserved magnetic-field-induced phase transitions and a field-orientation dependence that deviates from theoretical predictions near H ‖ c . A tetracritical point in the high field phase diagram and the second-order nature of the transitions eliminates several of the theoretically proposed spin structures for the high field phases and provides new guidance into the nature of the magnetic order in each phase. |
Friday, March 19, 2021 9:48AM - 10:00AM Live |
X39.00008: Observation of high order multi-magnon (n = 4 and 6) bound states in the frustrated triangular antiferromagnetic lattice FeI2 Anaelle Legros, Shang-Shun Zhang, Xiaojian Bai, Hao Zhang, Cristian Batista, Martin P Mourigal, Peter Armitage Spin waves (e.g. magnons) are the conventional elementary excitations of a magnetically ordered phase. However, other possibilities exist. For instance, magnon bound states can arise at low energy due to attractive magnon-magnon interactions and modify the low-temperature properties of the system. The most common case corresponds to two-magnon bound states (n = 2) in quasi-one-dimensional quantum magnets [1]. Here we study the frustrated spin-1 triangular antiferromagnetic lattice FeI2 [2] using time-domain terahertz spectroscopy. The spectra reveal a zoo of distinct multi-magnon quasiparticles at low energies, including up to six-magnon bound states, along with interactions between them. The energy-magnetic field excitation spectrum provides valuable information on the Hamiltonian of this peculiar material and is well reproduced by exact diagonalization calculations of a low-energy Hamiltonian for a dilute gas of interacting quasiparticles. The existence of these high order magnon bound states provides a novel platform to study multiparticle interactions and decays in a condensed matter setting. |
Friday, March 19, 2021 10:00AM - 10:12AM Live |
X39.00009: Effects of dislocations in triangular antiferromagnet NiGa2S4 Haoyu Wang, Oleg Tchernyshyov NiGa2S4 is a frustrated magnet on a triangular lattice with a strong antiferromagnetic third-neighbor exchange J3 and a weak ferromagnet first-neighbor exchange J1. Although the system has been studied for more than a decade [1], its behavior, particularly the lack of long-range order, remains poorly understood. Exotic scenarios have been proposed for its explanation, including the formation of a quadrupolar spin order that cannot be seen by the usual probes like neutrons [2]. We propose a different scenario based on a simple observation: the geometrical frustration of NiGa2S4 can be relieved by a lattice distortion similar to the case of the pyrochlore antiferromagnet [3]. Based on a generalized Imry-Ma argument, the spin-Peierls phase transition may be preempted by long-range-correlated strains of random edge dislocations. Using Monte Carlo simulation, we show that the ground state domain pattern matches the pattern of strain field from dislocations. |
Friday, March 19, 2021 10:12AM - 10:24AM Live |
X39.00010: Magnetic excitations affected by spin-lattice coupling in the S=3/2 triangular lattice antiferromagnet Ag2CrO2 Masaaki Matsuda, Sachith Dissanayake, Hiroyuki K. Yoshida, Masaaki Isobe, Matthew Brandon Stone Ag2CrO2 is an S=3/2 triangular lattice antiferromagnet in which long-range magnetic order with a 5-fold magnetic unit cell appears below the transition temperature (TN) of 24 K [1]. The long range magnetic order is accompanied by a structural transition. Inelastic neutron scattering experiments were performed to investigate the magnetic interactions, anisotropy, and correlations in this material. Above TN, diffuse scattering originating from the short-ranged magnetic correlations consistent with a 120-degree structure was observed. The magnetic excitations below TN were reproduced reasonably well using a linear spin-wave model with further-neighbor interactions and easy-axis anisotropy, which are predicted to be due to a previously proposed spin-lattice coupling [2]. |
Friday, March 19, 2021 10:24AM - 10:36AM Not Participating |
X39.00011: Muon investigations of magnetsm in the frustrated material LiYbO2. Eric Kenney, Mitchell Bordelon, Lorenzo J Posthuma, Stephen D Wilson, Michael John Graf Muon Spin Relaxation (µSR) has long been a preferred technique for examining the ground state of potential quantum spin liquid (QSL) candidates, as it is a local probe that is capable of discriminating between ordered and disordered magnetism, as well as static and dynamic magnetism. Recently there has been interest in LiYbO2, whose Jeff=1/2 moments are predicted to be frustrated. Recently published neutron diffraction experiments, along with theory, suggest that this material may instead experience an unusual form of incommensurate magnetic order, consisting of two phase-shifted sublattices. We performed µSR measurements and show that near 1 Kelvin the system transitions from a non-magnetic state to a strongly magnetic disordered state consistent with the unusual incommensurate order suggested by neutron diffraction. Additionally, we find evidence for weak dynamics, suggesting some fraction of the system may not magnetically order and instead remains in a frustrated state. |
Friday, March 19, 2021 10:36AM - 10:48AM Live |
X39.00012: Crystal Growth and Characterization of Yb - Based Triangular Lattice Borate Rabindranath Bag, Matthew Ennis, Sachith Dissanayake, Zhenzhong Shi, Alexander Kolesnikov, Jose A. Rodriguez-Rivera, Hui Wu, Craig Brown, Sara Haravifard The quest of understanding the geometrically frustrated magnets in condensed matter physics is an interesting topic as they seem to host a variety of exciting physics such as spin glass, spin ordered and quantum spin liquid state. One of such systems is rare earth borates family which consists of magnetic rare earth ions in a triangular lattice and rare earth ions are magnetically well separated by non-magnetic layers showing exotic ground state. We have successfully synthesized and grown the centimetric sized single crystal of Yb-based borate compound, Ba3Yb(BO3)3. The quality of the grown crystal was confirmed using x-ray/neutron diffraction, magnetometry, and heat capacity. The magnetic study on our grown crystal revealed the presence of anisotropic magnetic interactions between Yb3+ - Yb3+, and heat capacity shows no signature of long range magnetic ordering down to ~50 mK. In this talk, I will share our latest experimental results. |
Friday, March 19, 2021 10:48AM - 11:00AM Live |
X39.00013: High-field resonant torsion magnetometry as a probe of CEF Interactions and exchange in frustrated triangular lattice CsYbSe2 Christopher Pocs, Jie Xing, Athena S. Sefat, Minhyea Lee We probe magnetoanisotropy of the highly frustrated 2-dimensional triangular lattice antiferromagnet CsYbSe2, using resonant torsion magnetometry in pulsed fields up to 60 T. In recent years, the family of 112 systems of the form ARQ2 (A = Alkali, R = Rare Earth, Q = O, S, Se) has attracted much experimental and theoretical attention for its potential to realize a QSL with effective spin-1/2 rare-earth ions on the triangular lattice, a canonical geometry for frustrated magnetism. Our analysis of the high-field magnetotropic response of CsYbSe2, across a wide range of temperatures, provides an unambiguous determination of the crystal-electric-field parameters as well as leading order exchange interactions in CsYbSe2. In turn, this information is utilized to identify potential exotic spin states and to set clear boundaries for the applicability of existing spin models. We will also discuss possible experimental implications of QSLs for this family of rare-earth triangular lattice compounds. |
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