Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session B54: Triangular LatticesFocus
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Sponsoring Units: GMAG Chair: Duminda Sanjeew, University of Missouri Room: Room 306 |
Monday, March 6, 2023 11:30AM - 12:06PM |
B54.00001: Roller-Coaster in a Flatland: Magnetoresistivity in Eu-intercalated Graphite Invited Speaker: Alexander L Chernyshev Novel phenomena in magnetically-intercalated graphite has been a subject of much research in the 1980s, with the most enigmatic findings of that era being a dramatic, roller-coaster-like behavior of the magnetoresistivity in EuC6 compound, which remained unexplained until now. In our recent study, we have provided a long-awaited microscopic explanation of this behavior, demonstrating that the resistivity of EuC6, in which magnetic Eu2+ ions form a triangular lattice that is commensurate with the graphite honeycomb planes, is dominated by spin excitations in Eu-planes and their highly nontrivial evolution with the magnetic field. Together with our theoretical analysis, this study showcases the power of the synthetic 2D materials as a potential source of significant novel insights into the nature of exotic spin excitations such as fractionalized spinons in a quantum spin liquid. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B54.00002: A Schwinger boson theory of the 1/3 magnetization plateau on the triangular lattice Santanu Dey, Joseph Maciejko, Matthias Vojta The classical ground state of the spin 1/2 SU(2) Heisenberg model on the triangular lattice describe a unique noncollinear, coplanar ordering pattern. However, with the addition of an external magnetic field to the model, a degenerate classical ground state manifold arises. It has been known for a while that if the lattice is homogeneous and isotropic, a quantum fluctuation-driven ordering mechanism selects a coplanar configuration for the ground state and breaks the classical degeneracy. This order-by-disorder mechanism also leads to a gapped state for a select magnetic field range where the net magnetization is quantized at an 1/3 fraction of the classical spin moments. In this paper, we consider the Schwinger boson representation of SU(2) spins to demonstrate the order by disorder mechanism and the emergence of the 1/3 magnetization plateau with a variational analysis. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B54.00003: Itinerant Ferromagnetism in the Triangular Lattice Hubbard Model Prakash Sharma, Ignatius Sebastian, Hitesh J Changlani The Hubbard model was initially proposed to explain kinetic ferromagnetism (FM) in transition metals. While FM is indeed stabilized at infinite onsite Coulomb repulsion U (as pointed out by Nagaoka and Thouless for the case of one hole at half filling), this is not the case at finite U and filling for the bipartite square (relevant to materials such as the cuprates) and cubic lattices. Frustration requires that these qualitative results be revisited, which motivates our present study. We explore the phase diagram of the Hubbard model above half filling (f=1) on the frustrated triangular lattice and demonstrate its tendency to stabilize a weak but robust FM ground state. In contrast to previous mean field approaches, our many-body calculations, based on the density matrix renormalization group, reveal that the FM is stabilized in a relatively narrow region in phase space, a finding of possible relevance to recent transition metal dichalcogenide (moire) based experiments. We estimate the critical U between the unpolarized paramagnet and FM phases, finding the latter to have an itinerant character. We then seek an explanation of the kinetic origin of FM within the Stoner theory, based on the occurrence of a van Hove singularity at f=1.5, and conclude by constructing a variational ansatz for the ground state wavefunction. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B54.00004: Competition between stripy and 120-degree spin correlations in the spin glass ground state of the triangular quantum antiferromagnet ErMgGaO4 Hsiao-Yuan (Symphony) Huang, Sylvain Petit, Zachary W Cronkwright, Evan M Smith, Suvam Bhattacharya, Jean-Marc Zanotti, Quentin Berrod, Edwin Kermarrec, Bruce D Gaulin ErMgGaO4 is a quantum antiferromagnet wherein pseudospin 1/2, Er3+ degrees of freedom |
Monday, March 6, 2023 12:42PM - 12:54PM |
B54.00005: Sign-problem-free effective models of spin-1/2 Heisenberg antiferromagnetism on the triangular lattice Henry J Shackleton A long-standing problem in the study of frustrated magnetism is an ubiquitous sign problem which often prevents large-scale numerical studies via Monte Carlo sampling. We present an effective lattice model of triangular lattice antiferromagnetism, using a Schwinger boson representation, that captures phases with 120° magnetic order, spin liquid phases, and valence bond solid (VBS) ordering. This is a theory of bosonic spinons on a triangular lattice coupled to an odd Z2 gauge field. A Berry phase term connected to the half-integer spin introduces a sign problem and naively renders the problem inaccessible through Monte Carlo techniques. Through a series of exact transformations, we derive a sign-problem-free representation of this model. Numerical results are presented which shed light on the nature of the critical theories separating the various phases in this model; in particular, the transition between 120° magnetic order and VBS order is analyzed. |
Monday, March 6, 2023 12:54PM - 1:06PM |
B54.00006: Effects of Pressure on Electronic and Magnetic Properties of Bulk NiI2 Jesse Kapeghian, Antia S Botana, Danila Amoroso, Matthieu J Verstraete, Connor A Occhialini, Luiz Martins, Qian Song, Jesse S Smith, Joshua J Sanchez, Jing Kong, Riccardo Comin Transition metal dihalides have recently garnered interest in the context of two-dimensional van der Waals magnets as their underlying geometrically frustrated triangular lattice leads to interesting competing exchange interactions. In particular, NiI2 is a centrosymmetric magnetic semiconductor that has been long known for its exotic helimagnetism in the bulk. Recent breakthrough experiments have shown that the helimagnetic state survives down to the monolayer limit with a layer-dependent magnetic transition temperature that suggests a relevant role of the interlayer coupling. Here, we explore the evolution of the electronic structure and magnetic exchange interactions in NiI2 as a function of external pressure using first-principles calculations and Monte Carlo simulations. We find that the leading interlayer coupling is an antiferromagnetic second-nearest neighbor interaction that increases monotonically with pressure. The ratio between isotropic third- and first-nearest neighbor intralayer exchanges, which determines the magnetic propagation vector q of the helimagnetic ground state, monotonically increases in magnitude with pressure. As a consequence, our Monte Carlo simulations show a monotonic increase in the magnetic transition temperature indicating that pressure is an effective means to tune the magnetic ground state of NiI2. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B54.00007: Experimental investigation of the quantum phase transitions in spin-1/2 triangular lattice antiferromagnet Lu Li, Dechen Zhang, Kuan-Wen Chen, Yuan Zhu, Guoxin Zheng, Haidong Zhou The two-dimensional spin-1/2 triangular lattice antiferromagnet (TLAF) is one of the simplest geometrically frustrated quantum magnets. The recently synthesized Na2BaCo(PO4)2 (NBCP) is an ideal material incarnation of the spin-1/2 TLAF. Theoretically, it was proposed that the NBCP hosts a spin supersolid ground state that breaks both the lattice translational and spin U(1) symmetries. The applied magnetic field H could drive the system through Berezinskii-Kosterlitz-Thouless (BKT) melting of the spin supersolidity and many other richer quantum phases. However, the detection of these transitions is a huge challenge because the transitions onset at extremely low temperatures T at around 60 mK, and the measurement of the magnetic susceptibility requires high sensitivity. With the help of our newly developed gradient force magnetometer in a dilution refrigerator, we clearly map out the contour diagram of the magnetic susceptibility in the H-T phase diagram in T as cold as 20 mK. The sensitivity of the measurement is comparable to the commercial magnetometer. These results offer an ideal platform for investigations on the field-tunable quantum phase transitions and BKT melting of the spin supersolidity. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B54.00008: Neutron diffraction studies of the magnetic phase diagram of the effective spin-1/2 triangular lattice antiferromagnet Na2BaCo(PO4)2 Ryutaro Okuma, Pascal Manuel, Qing Huang, Haidong Zhou, Radu Coldea We report single crystal time-of-flight neutron diffraction measurements as function of applied magnetic field in the effective spin-1/2 stacked triangular lattice antiferromagnet Na2BaCo(PO4)2, recently proposed as a candidate to display unconventional magnetic behaviour with a rich phase diagram in applied c-axis field including a 1/3rd magnetization plateau phase [1,2]. We characterize the magnetic diffraction pattern in the various phases and discuss models of the magnetic structure evolution as a function of applied magnetic field up to saturation. [1] R.D. Zhong et al, Proc. Natl Acad. Sci. USA 116, 14505 (2019). [2] N. Li et al. Nat. Commun. 11, 1-9 (2020). |
Monday, March 6, 2023 1:30PM - 1:42PM |
B54.00009: Low-temperature magnetism in the triangular lattice materials CeCl3 and CeBr3 Matthew A Cothrine, David G Mandrus, Stephen E Nagler, Adam A Aczel, Matthew B Stone, Yasumasa Takano, Luis Stand There is currently great interest in systems with J = 1/2 ground state and Ising-like interactions that may be geometrically frustrated, as in the triangular lattice, or frustrated by competing interactions, like the honeycomb Kitaev model. This interest has spurred our investigation of the triangular lattice rare earth materials CeCl3 and CeBr3, where the Ce3+ ion is expected to have an effective J = 1/2 ground state. Some magnetic properties of these materials were studied many years ago but prior to this investigation there had been no direct measurements of the magnetic order or excitations using neutron scattering. Our recent magnetic characterization has revealed the onset of short-range order at around 250 mK before two successive transition in long-range order at around 110 mK and 50 mK for CeCl3. We also report neutron scattering investigations of crystal field excitations in CeBr3, confirming the J=1/2 ground state, and neutron diffraction measurements of the magnetic order in CeCl3, showing that the system orders antiferromagnetically at low temperature with an ordering wave-vector (1/3 1/3 1/2). |
Monday, March 6, 2023 1:42PM - 1:54PM |
B54.00010: Centrosymmetric lattice with frustrated triangular planes of Gd ions: GdNiAl4Ge2 Keke Feng, Jorge R Galeano-Cabral, Olatunde Oladehin, Kaya Wei, Ryan E Baumbach There is ongoing interest in magnetically frustrated metals, where the interplay between structural, charge, and spin degrees of freedom often produce novel phenomena. Motivated by this, we recently investigated the compounds LnAuAl4Ge2 (Ln = lanthanide), which feature triangular nets of Ln ions and exhibit complex magnetism in some cases (e.g., Ln = Gd and Tb) [1, 2]. Here we report results for the transition metal analog GdNiAl4Ge2 and its nonmagnetic variant LuNiAl4Ge2. Magnetic, thermodynamics and electrical transport measurements reveal that the change from Au → Ni strongly impacts the ground state magnetism. In particular, we find evidence for antiferromagnetic-like ordering in small magnetic fields, which strongly evolves with increasing field and exhibits hysteresis over a limited part of the temperature (T )-magnetic field (H) phase diagram. We will present a detailed T − H phase diagram and discuss evidence for non-trivial spin textures or glassy behavior in this compound. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B54.00011: Synthesis and Characterization of NdCd3P3 and PrCd3P3 Azzedin R Jackson, Juan Chamorro, Farnaz Kaboudvand Geometrically frustrated magnetic systems frequently feature triangular or hexagonal arrangements of magnetic ions with competing magnetic interactions, which can give rise to exotic magnetic ground states. There are several material systems with these triangular/hexagonal structural motifs that have been studied extensively, but one material system that has remains underexplored is the phosphide family LnCd3P3, possessing well-separated Ln3+ ions set in a triangular lattice, which makes this system another avenue to study frustrated magnetism and the resulting exotic magnetic ground states. Previously, the properties of the LaCd3P3 and CeCd3P3 have been examined in detail, and the crystal structure of PrCd3P3 has been studied with X-Ray Diffraction. In this work, we first introduce a new method for synthesizing high quality polycrystalline samples of these LnCd3P3 compounds. We then expand the phase space by introducing NdCd3P3. Finally, we present the data from resistivity, heat capacity, and magnetization measurements of polycrystalline samples of NdCd3P3 and PrCd3P3. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B54.00012: Commensurate and incommensurate antiferromagnetic orderings in CaMn2P2 and SrMn2P2 revealed by NMR YUJI FURUKAWA, Qing-Ping Ding, Hyung-Cheol Lee, N.S. Sangeetha, Santanu Pakhira, David C Johnston Recently much attention has been paid to the Mn-based compounds with AMn2Pn2 (A= Sr, Ca, Ba, and Pn = P, As, Sb, Bi) since the systems show a rich variety of magnetic properties with different crystal structures. Different from BaMn2As2 which shows the body-centered tetragonal ThCr2Si2-type structure, (Ca,Sr)Mn2Pn2 (Pn = P, As, Sb, Bi) crystallize in the trigonal CaAl2Si2-type structure where the Mn ions form a triangular lattice bilayer which can be considered as a corrugated Mn honeycomb sublattice. CaMn2P2 and SrMn2P2 have been reported to exhibit first-order antiferromagnetic (AFM) transitions at TN = 69.8 K and 53 K, respectively [1]. In this study, we have carried out 31P nuclear magnetic resonance (NMR) measurements on those systems to investigate the magnetic properties from a microscopic point of view. In the case of CaMn2P2, we observed a clear signature of first-order AFM transition at TN in 31P NMR data and found distinct splittings of 31P NMR lines in the AFM state. In contrast, broad NMR spectra were observed in the AFM state of SrMn2P2, indicating a distribution of internal fields at the P site. Those results indicate that the AFM states are commensurate and incommensurate in CaMn2P2 and SrMn2P2, respectively. |
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