Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M46: Quasi2D Frustration: Honeycomb Lattice and Other Geometries 
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Sponsoring Units: GMAG Chair: Kate Ross, Colorado State University Room: 708 
Wednesday, March 4, 2020 11:15AM  11:27AM 
M46.00001: Topological Quantum ManyBody Scars in Quantum Dimer Models Alexander Seidel, Julia Wildeboer, Anne E. B. Nielsen, Onur Erten We construct twodimensional lattice models with quantum dimer degrees of freedom that violate the eigenstate thermalization hypothesis (ETH) by featuring quantum manybody scars in their excitation spectrum. These scars consist of single exactly known excited eigenstates with atypical (area law) entanglement entropy. We explicitly construct such models for the kagome and checkerboard lattices. We compute entanglement entropy numerically for the surrounding states, and analytically for the scar states themselves. Furthermore, we corroborate the nonintegrable nature of these quantum dimer models by studying the statistics of the spacings between consecutive energy levels. 
Wednesday, March 4, 2020 11:27AM  11:39AM 
M46.00002: Novel Quantum Phase Transition of the ShastrySutherland Model Toru Sakai, Hiroki Nakano The ShastrySutherland model  the S = 1/2 Heisenberg antiferromagnet on the square lattice accompanied by orthogonal dimerized interactions  is studied by the numericaldiagonalization method. Largescale calculations provide results for larger clusters that have not been reported yet. The present study successfully captures the phase boundary between the dimer and plaquettesinglet phases and clarifies that the spin gap increases once when the interaction forming the square lattice is increased from the boundary. Our calculations strongly suggest that in addition to the edge of the dimer phase given by J_{2}/J_{1}∼0.675 and the edge of the Neelordered phase given by J_{2}/J_{1}∼0.76, there exists a third boundary ratio J_{2}/J_{1}∼0.70 that divides the intermediate region into two parts, where J_{1} and J_{2 }denote dimer and squarelattice interactions, respectively. We report the result from the investigation about this possible novel quantum phase transition in the plaquette singlet phase[1]. 
Wednesday, March 4, 2020 11:39AM  11:51AM 
M46.00003: Antiferromagnetictoferrimagnetic phase transition in frustrated polar magnet CaBaCo_{4}O_{7} Tsuyoshi Omi, Yoshito Watanabe, Nobuyuki Abe, Yusuke Tokunaga, Akiko Nakao, Koji Munakata, Hajime Sagayama, Takahisa Arima Magnetic frustration often plays important roles in multiferroic properties as is exemplified by the electric polarization induced by the spiral magnetic order. CaBaCo_{4}O_{7 }belongs to the orthorhombic space group Pbn2_{1}. Magnetic Co ions form Kagomé and triangular lattice layers, which alternately stack along the caxis. CaBaCo_{4}O_{7} shows a ferrimagnetic transition at T_{c} ∼ 60 K at zero magnetic field. CaBaCo_{4}O_{7} is a multiferroic material hosting magnetic frustration[1]. It exhibits an electric polarization change of about 17 mC/m^{2} at the ferrimagnetic transition which is the largest among all the multiferroic materials so far[2]. The specific heat and the electric permittivity of single crystal CaBaCo_{4}O_{7} exhibits another anomaly at T_{N}∼69 K slightly higher than T_{c} in zero magnetic field, while the origin of the anomaly was not clarified[2]. 
Wednesday, March 4, 2020 11:51AM  12:03PM 
M46.00004: Signswitching of dimer correlations in SrCu_{2}(BO_{3})_{2} under hydrostatic pressure Simon Bettler, Lena Stoppel, Zewu Yan, Severian Gvasaliya, Andrey Zheludev Magnetic and vibrational excitations in SrCu_{2}(BO_{3})_{2} are studied using Raman spectroscopy at hydrostatic pressures up to 34 kbar and temperatures down to 2.6 K. The frequency of a particular optical phonon, the socalled pantograph mode, shows a very strong anomalous temperature dependence below about 40 K. We link the magnitude of the effect to the magnetic exchange energy on the dimer bonds in the SutherlandShastry spin lattice in this material. The corresponding dimer spin correlations are quantitatively estimated and found to be strongly pressure dependent. At around P_{2}~22 kbar they switch from antiferromagnetic to being predominantly ferromagnetic. 
Wednesday, March 4, 2020 12:03PM  12:15PM 
M46.00005: Large spin fluctuation in the magnetization process of S=1/2 frustrated square lattice model Tsuyoshi Okubo In the frustrated spin systems, a lot of interesting phenomena including noncollinear magnetic orders, magnetization plateaus and spin liquids occur. Such frustrated interactions often appear in geometrically frustrated lattices, such as triangular, kagome or pyrochlore lattices. In addition to these lattice, when we consider further neighbor interactions or combination of ferromagnetic and antiferromagnetic interactions, frustrations can happen even in the square lattice. 
Wednesday, March 4, 2020 12:15PM  12:27PM 
M46.00006: Quantum Phases Diagram of the Plaquette State of the ShastrySutherland Compound SrCu_{2}(BO_{3})_{2} Sara Haravifard, Zhenzhong Shi, Sachith Dissanayake, David E Graf, Philippe R. Corboz, Frederic Mila, Daniel Silevitch, Thomas F Rosenbaum, Hanna Dabkowska, Casey Marjerrison The ShastrySutherland compound SrCu_{2}(BO_{3})_{2 }features 2D layers of Cu^{2+} S=1/2 spin dimers which are orthogonal to each other. The ground state of the system is determined by the relative strength of the nearest neighbor and nextnearest neighbor interactions, J and J’ respectively. The ratio of J/J’ can be tuned continuously by application of hydrostatic pressure. The ground state changes from a spin dimer singlet state at ambient pressure to an antiferromagnet state at high pressure. At intermediate pressure a novel 4spin plaquette singlet state has recently been reported. However, the nature of this plaquette state and how it evolves into other phases remains unclear. Here, we report a comprehensive study of the quantum phase diagram of the plaquette state by tuning temperature, pressure, magnetic field, and chemical doping. We mapped out the evolution of the ground states using complementary techniques such as magnetic susceptibility, magnetization and neutron scattering measurements. The results provide insights into the nature of the plaquette state, and also has implications in areas such as studies of deconfined quantum criticality. 
Wednesday, March 4, 2020 12:27PM  12:39PM 
M46.00007: Critical properties of a fractionally frustrated XY model on the square lattice Tasrief Surungan, Zohar Nussinov

Wednesday, March 4, 2020 12:39PM  12:51PM 
M46.00008: Exact Solution and Correlations of a Quantum Dimer Model on the Checkerboard Lattice Julia Wildeboer, Zohar Nussinov, Alexander Seidel For decades, constrained models with dimer degrees of freedom have been a powerhouse of statistical physics and various branches of theoretical and mathematical physics, in particular aspects of quantum magnetism. For analytic purposes, their utility is usually limited to models defined on planar lattice graphs, where, thanks to a powerful theorem by Kasteleyn, many questions can be answered exactly. Here we present analytic results on a special dimer model on a {\it nonplanar} checkerboard lattice of interacting dimers, which does not permit for parallel dimers to surround diagonal links. We report exact results on the enumeration of closed packed dimer coverings on finite checkerboard lattices under periodic boundary conditions. Furthermore, we comment on the behavior of the dimerdimer correlations and find that the correlations between any two dimers vanish identically if their distance is larger than two unit cells. Connections with $\mathbb{Z}_{2}$ gauge theory, known from planar models, are extended to the present case. 
Wednesday, March 4, 2020 12:51PM  1:03PM 
M46.00009: Magnetic structure of the stuffed honeycomb antiferromagnet GdInO_{3} Erxi Feng, Xianghan Xu, Eve Emmanouilidou, Jae Wook Kim, Yan Wu, LEI DING, Alexander Kolesnikov, Ni Ni, SangWook Cheong, Huibo Cao Rareearth indium oxides RInO_{3} (R = rare earth), in which R^{3+} ions occupy two nonequivalent sites forming a honeycomb lattice with a superimposed triangular lattice (socalled stuffed honeycomb lattice), present an excellent platform to study the combination of two different frustrated lattices. Since the total angular moment L of Gd^{3+} ion is zero, GdInO_{3} is expected as pure spin magnetism and may be considered as a classical Heisenberg spin system in the stuffed honeycomb lattice. A high quality isotope single crystal ^{160}GdInO_{3} was synthesized for neutron scattering studies to avoid the high neutron absorption of natural Gd. The specific heat measurement shows that the compound exhibits two step magnetic phase transitions at 2.2 K and 1.08 K corresponding to two different antiferromagnetic phases that were characterized by single crystal neutron diffraction. These phases transition may be explained via the orderbydisorder mechanism. 
Wednesday, March 4, 2020 1:03PM  1:15PM 
M46.00010: Frustrated magnetic interactions in an S=3/2 bilayer honeycomb lattice compound Bi_{3}Mn_{4}O_{12}(NO_{3}) Masaaki Matsuda, Sachith Dissanayake, Douglas L Abernathy, Yiming Qiu, John Copley, Nobuhiro Kumada, Masaki Azuma Inelastic neutron scattering study has been performed in an S=3/2 bilayer honeycomb lattice compound Bi_{3}Mn_{4}O_{12}(NO_{3}) at ambient and high magnetic fields [1]. Relatively broad and monotonically dispersive magnetic excitations were observed at ambient field, where no long range magnetic order exists. In the magnetic fieldinduced longrange ordered state at 10 T, the magnetic dispersions become slightly more intense, albeit still broad as in the disordered state, and two excitation gaps, probably originating from an easyplane magnetic anisotropy and intrabilayer interactions, develop. Analyzing the magnetic dispersions using the linear spinwave theory, we estimated the intraplane and intrabilayer magnetic interactions, which are almost consistent with those determined by ab initio density functional theory calculations [2], except the third and fourth neighbor intrabilayer interactions. Most importantly, as predicted by the theory, there is no significant frustration in the honeycomb plane but frustrating intrabilayer interactions probably give rise to the disordered ground state. 
Wednesday, March 4, 2020 1:15PM  1:27PM 
M46.00011: Observations of antiferromagnetic, antiferroelectric and ferroelastic orderings in honeycomblattice Mn_{2}V_{2}O_{7} HungCheng Wu, DongJie Hsieh, TsungWen Yen, PoJung Sun, D. Chandrasekhar Kakarla, JimLong Her, Y. H. Matsuda, ChungKai Chang, YuChun Chuang, YenChung Lai, Melissa Gooch, Liangzi Deng, Kyle Grant Webber, Ching (Paul) W Chu The dielectric and magnetic anomalies were observed in Mn_{2}V_{2}O_{7} between 275 K and 300 K. Isothermal capacitancestress hysteresis loop measurements along with crystallographic Aizu notation supported a martensitic phase transition (T_{M}) driven ferroelastic behavior near room temperature. Another dielectric anomaly was also observed near the longrange antiferromagnetic (AFM) ordering temperature (T_{N} ~ 16.4 K) along with noticeable magnetodielectric (MD) coupling below T_{N}, signifying the multiferroic nature of Mn_{2}V_{2}O_{7}. With increasing pressure, the antiferromagnetic ordering (T_{N}) greatly increased, while the (T_{M}) was suppressed. Taking all of these comprehensive research findings into account, we suggest that Mn_{2}V_{2}O_{7} is a unique multifunctional material with the coexistence of antiferromagnetic, antiferroelectric and ferroelastic orderings. 
Wednesday, March 4, 2020 1:27PM  1:39PM 
M46.00012: NMR study on the honeycomblattice antiferromagnet Na_{2}Co_{2}TeO_{6} Weiqiang Yu, Ze Hu, Yuan Li, Weiliang Yao The honeycomblattice magnetic materials have caused a lot of research interests recently, because of possible realization of Kitaev or proximate Kitaev quantum spin liquid in these systems. Na_{2}Co_{2}TeO_{6}, as a new honeycomblattice antiferromagnet, has a zigzag magnetic order which can be suppressed by magnetic field. Here we report our NMR studies on Na_{2}Co_{2}TeO_{6} single crystals, and show rich properties revealed in this system both at zero field and at finite fields. 
Wednesday, March 4, 2020 1:39PM  1:51PM 
M46.00013: Cooperative liquidlike paramagnetic state in nanoengineered honeycomb lattice George Yumnam, Yiyao Chen, Jiasen Guo, Haile Arena Ambaye, Valeria Lauter, Deepak K Singh Geometrically frustrated honeycomb structured artificial magnetic lattice has emerged as a testbed to explore the competing physics of energy vs. entropy in a thermally tuned magnetic phase transition. A magnetic honeycomb lattice with competing exchange interactions between Ising moments is theoretically predicted to exhibit disordered magnetic state with macroscopic degeneracy. We demonstrate the realization of a liquidlike magnetic state, comprised of low integer and energetically forbidden high integer magnetic charges, in nanostructured magnetic honeycomb lattice of ultrasmall, sub12 nm, connecting elements. Magnetic charges, related to magnetic moment and interacting via magnetic Coulomb's interaction, act as quantum mechanical entities. Detailed polarized neutron reflectometry measurements on magnetic honeycomb reveal a robust degenerate ground state at low temperature, which remains minimally affected by magnetic field application. Our finding provides a new vista to investigate quantum mechanical phenomena from the perspective of dynamic magnetic charges, instead of magnetic moments, in a classical system. 
Wednesday, March 4, 2020 1:51PM  2:03PM 
M46.00014: Field induced phase transition in the classical honeycomb Gamma model Zhongzheng Tian, Zhijie Fan, Preetha Saha, GiaWei Chern Recent studies have indicated the importance of the symmetric aniostropic exchange interaction, also called the Γ term, in the socalled Kitaev materials. Moreover, a new type of classical spin liquid was shown to be the ground state of the classical Γ model on the honeycomb lattice [1]. In our previous paper [2], we further demonstrated that thermal orderbydisorder drives the system toward a novel plaquette ordering that spontaneously breaks the lattice translation symmetry. In this work, we study the effects of magnetic field on the plaquetteordered state. Our extensive Monte Carlo simulations uncover a fieldinduced phase transition above which the √3×√3 flux order is replaced by a new spin order. We will present our characterization of this intermediate phase and discuss the nature of the phase transitions. [1] I. Rousochatzakis and N. B. Perkins, Phys. Rev. Lett. 118, 147204 (2017). [2] P. Saha, Z. Fan, D. Zhang, and G.W. Chern, Phys. Rev. Lett. 122, 257204 (2019). 
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