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 G56: Quantum Spin Liquids, Theory I |
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Sponsoring Units: GMAG Chair: Radu Coldea, University of Oxford Physics Department Room: Room 304 |
Tuesday, March 7, 2023 11:30AM - 11:42AM |
G56.00001: Vison crystals, chiral and crystalline topological phases in Yao-Lee model Muhammad Akram, Emilian M Nica, Onur Erten We perform a variational analysis in single and bilayer Yao-Lee model as a function of the external magnetic field (B) and Dzyaloshinskii−Moriya interaction (DMI). We uncover a rich phase diagram where a variety of vison crystals are stabilized. For in-plane B, these phases are mostly gapless and gapped for out-of-plane B. The gapped phases are further classified by a Chern number that determines the number of chiral edge modes. We also elucidate crystalline topological phases protected by mirror symmetry. |
Tuesday, March 7, 2023 11:42AM - 11:54AM |
G56.00002: Competing quantum spin liquids, gauge fluctuations, and anisotropic interactions in a breathing pyrochlore lattice Li Ern Chern, Yong Baek Kim, Claudio Castelnovo Using projective symmetry group analysis, we classify the possible quantum spin liquids on the S=1/2 breathing pyrochlore magnet, which results in 40 Z2 spin liquids and 16 U(1) spin liquids that respect the space group and the time reversal symmetry. As an application, we consider the antiferromagnetic Heisenberg model, which is proposed to be the dominant interaction in the candidate material Ba3Yb2Zn5O11. Focusing on the U(1) spin liquid Ansätze, we find that only two of them are physical when restricted to this model. We present an analytical solution to the parton mean field theory for each of these two U(1) spin liquids. It is revealed that one of them has gapless, while the other has gapped, spinon excitations, but they are equal in energy regardless of the degree of breathing anisotropy. The two U(1) spin liquids can be distinguished by the low temperature heat capacity contribution from the quadratically dispersing gapless spinons, which is further shown to be unaffected by gauge fluctuations within the random phase approximation. Finally, we demonstrate that a small Dzyaloshinskii-Moriya interaction lifts the degeneracy between the two U(1) spin liquids, and it eventually disconnects the lattice into independent tetrahedra at strong coupling. [Phys. Rev. B 106, 134402 (2022)] |
Tuesday, March 7, 2023 11:54AM - 12:06PM |
G56.00003: Symmetry fractionalization in quantum spin ice Félix Desrochers, Li Ern Chern, Yong-Baek Kim Symmetry fractionalization is a ubiquitous feature of topologically ordered states that can be used to classify different symmetry-enriched topological phases and reveal some of their unique experimental signatures. Despite its vast popularity, there is currently no available framework to study symmetry fractionalization of quantum spin ice (QSI) — a U(1) quantum spin liquid (QSL) on the pyrochlore lattice supporting emergent photons — within the most widely used theoretical framework to describe it, gauge mean-field theory (GMFT). In this work, we provide an extension of GMFT that allows for the classification of space-time symmetry fractionalization. The construction classifies all GMFT Ansätze that yield physical wavefunctions invariant under given symmetries and a specific low-energy gauge structure. As an application of the framework, we first show that the only two Ansätze with emergent U(1) gauge fields that respect all space-group symmetries are the well-known 0- and π-flux states. We then showcase how the framework may describe QSLs beyond the currently known ones by classifying chiral U(1) QSI. We find two new states described by π/2- and 3π/2-fluxes of the emergent gauge field threading the hexagonal plaquettes of the pyrochlore lattice. We then examine how the different ways translation symmetries fractionalize for all these states lead to unique experimentally relevant signatures and compute their respective inelastic neutron scattering cross-section to illustrate the argument. We end by discussing how our framework can be extended to study Z2 QSLs born out of spinon pairs condensation, QSI on the breathing pyrochlore lattice where inversion symmetry is broken, and the dipolar-octupolar case relevant for Ce2Zr2O7. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G56.00004: Exact diagonalization of Pyrochlores using a symmetry-derived method Kyle P Hall, Stephanie Curnoe, CHEN WEI The study of quantum magnetics often involves the calculation of large, complex models. Optimized methods with which such calculations can be done are desirable to make research of the quantum properties of materials tenable. In this study, we solve the Hamiltonian for spin-1/2 pyrochlore magnet systems with nearest-neighbour exchange interactions and multiple cell sizes using exact diagonalization. Group theoretical methods used to reduce the complexity of the problem - allowing us to completely block-diagonalize the Hamiltonian for systems of significant size efficiently - will be discussed. The results produced using this method are used to examine quantum entanglement of the system within the four-parameter space of the general model of nearest-neighbour exchange interactions. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G56.00005: Liquid-to-Liquid Transition in a Spin Model on the Pyrochlore Lattice Daniel Lozano-Gomez, Vincent Noculak, Rajiv R Singh, Yasir Iqbal, Johannes Reuther, Michel J P Gingras One of the foremost goals in the study of pyrochlore magnetism is the search for spin-liquid phases composed of highly-disordered yet strongly correlated states. These phases are usually found in Hamiltonians possessing a highly degenerate ground state manifold preventing the onset of long-range order. However, this degeneracy does not guarantee the realization of a low-temperature spin-liquid as the phenomenon known as order-by-disorder may collapse the system into a long-range ordered phase by selecting entropically favorable spin configurations. In this work, we present a spin model on the pyrochlore lattice that realizes a novel classical spin-liquid at intermediate temperatures, collapsing into another spin-liquid phase at low temperatures. We argue that the rapid crossover between both phases has an entropic origin, providing the first realization of an order-by-disorder selected spin-liquid. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G56.00006: Magnetoelectric polarizability in bosonic insulators Gautam K Naik, Michael Flynn, Christopher R Laumann
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Tuesday, March 7, 2023 12:42PM - 12:54PM |
G56.00007: Quantum effects on unconventional pinch point singularities Johannes Reuther, Nils Niggemann, Yasir Iqbal Fracton phases are a particularly exotic type of quantum spin liquid where the elementary quasiparticles are intrinsically immobile. These phases may be described by unconventional gauge theories known as tensor or multipolar gauge theories, characteristic for so-called type-I or type-II fracton phases, respectively. Both variants have been associated with distinctive singular patterns in the spin structure factor, such as multifold pinch points for type-I and quadratic pinch points for type-II fracton phases. Here, we assess the impact of quantum fluctuations on these patterns by numerically investigating the spin-1/2 quantum version of a classical spin model featuring exact realizations of multifold and quadratic pinch points, as well as an unusual pinch line singularity. Based on large scale pseudo fermion and pseudo Majorana functional renormalization group calculations we take the intactness of these spectroscopic signatures as a measure for the stability of the corresponding fracton phases. We find that in all three cases, quantum fluctuations significantly modify the shape of pinch points or lines by smearing them out and shifting signal away from the singularities. This may indicate the fragility of fracton phases and allows us to identify characteristic features of their remnants. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G56.00008: Parton construction for Dipolar-Octupolar spin liquids in pyrochlore Sambuddha Sanyal, Krushna C Sahu We study the uniform U (1) quantum spin liquid (QSL) with low-energy fermionic quasiparticles for pyrochlore magnets with dipolar-octupolar symmetry, employing a fermionic parton mean field theory approach. Self-consistent calculations stabilize an uniform U (1) QSL with both gapped and gapless parton excitations. We analyse parton mean field solutions both with and without time-reversal symmetry. In the stable U(1) QSL ground state we charecterise low-temperature specific heat behaviour that could be unique signature of these fermionic U(1) QSL phases. Thus, this provides a possible way to understand the metallic specific heat response in Nd2ScNbO7. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G56.00009: Solvable dimer model on the nonplanar ruby lattice Julia S Wildeboer, Zohar Nussinov, Thomas Iadecola, Alexander Seidel Inspired by recent work discussing the quantum simulation of dimer models with Rydberg atoms placed |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G56.00010: Anisotropic Antiferromagnetic Heisenberg Model on a Bilayer Triangular Lattice Junyi Zhang, Tong Chen The antiferromagnetic Heisenberg model on the triangular lattice (AFHTL) continues to attract attention half a century after Anderson’s proposal that it might support a resonating valence bond state. The geometric frustration as well as thermal and quantum fluctuations make the AFHTL a key model for realizing unique collective phenomena, including order by disorder and various types of emergent quasi-particles. Recent studies of magnetic materials on the triangular lattice and of transition metal dichalcogenide moiré materials motivate us to study the effects of interlayer couplings on the AFHTL while remaining in two dimensions. We consider an anisotropic antiferromagnetic Heisenberg model on a bilayer triangular lattice with AA stacking. We show that the interlayer coupling along the vertical bond, although it does not introduce additional geometric frustration, enhances quantum fluctuation and destabilizes Néel order. In the strong interlayer coupling limit, the ground state becomes paramagnetic singlet dimers. Thus a spin liquid phase or a quantum critical point is expected in-between. In the strong easy-axis anisotropic (Ising) limit, we find the interlayer coupling tends to suppress the quantum fluctuations arising from a transverse magnetic field. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G56.00011: Entanglement and separability of Rokhsar-Kivelson and resonating valence-bond states Gilles Parez Entanglement and separability are two opposite yet intertwined notions in quantum mechanics. A quantum state is said to be entangled if it is not separable, and vice versa. Quantifying how entangled two subsystems are remains a challenging problem, which has led to important insights in the context of quantum many-body systems. In this talk, we discuss entanglement and separability of dimer Rokhsar-Kivelson (RK) states and resonating valence-bond (RVB) states. For dimer RK states on general tilable graphs, we prove the exact separability of the reduced density matrix of two disconnected subsystems, implying the absence of entanglement between the subsystems. For RVB states, we show separability for disconnected subsystems up to exponentially small terms in the distance d between the two subsystems. We argue that separability does hold in the scaling limit, even for arbitrarily small ratio d/L, where L is the characteristic size of the subsystems. Our results hold irrespective of the underlying graph (which include square and triangular lattices), and hence suggest that separability (up to exponentially small terms) between disjoint regions is a universal feature of quantum spin liquids. In the case of adjacent subsystems for the RK states, we derive exact results for the logarithmic negativity in terms of partition functions of the underlying statistical model, and recover the known result for the Rényi-1/2 entropy in the limit of complementary subsystems. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G56.00012: Neutron Scattering Signatures of Dipolar-Octupolar Spin Liquids Benedikt Placke Dipolar-Octupolar pyrochlores have generated much attention recently due to their capacity to host novel “symmetry enriched” topological phases, while at the same time being described by a relatively simple model Hamiltonian. However, the hybrid nature of the localized magnetic moments in these compounds significantly alters their response to external magnetic fields as well as neutron scattering. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G56.00013: U(1) Quantum Spin Liquids in 3+1D using Rydberg Interactions – a proposal Jeet Shah, Gautam Nambiar, Alexey V Gorshkov, Victor M Galitski Quantum Spin Liquids are exotic phases of matter with fractional excitations whose ordering is usually invisible to local order parameters. Obtaining conclusive experimental evidence for such states in solid-state systems remains an outstanding problem. With recent proposals and an experiment showing preliminary signs of a Z2 topological order, arrays of neutral atoms with Rydberg interactions have emerged as a promising platform to realize a spin liquid. In this work, we propose a way to realize a U(1) Quantum Spin Liquid in 3 spatial dimensions from Rydberg interactions. We study the phase diagram as a function of experimental parameters using a gauge mean field theory approach, considering the effect of long-range van der Waals interactions. We also suggest experimental probes for distinguishing the deconfined phase (quantum spin liquid) from a confined phase. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G56.00014: Emergence of Gapless Quantum Spin Liquid from Deconfined Quantum Critical Point Wenyuan Liu, Juraj Hasik, Shoushu Gong, Didier Poilblanc, Wei-Qiang Chen, Zhengcheng Gu Quantum spin liquids (QSLs) as novel phases of matter with long-range entanglement and deconfined quantum critical points (DQCPs) as descriptions for unconventional phase transitions between two ordered states beyond the standard paradigm, such as the transition between antiferromagnetic (AFM) and valence-bond solid (VBS) phases, are two representative emerging phenomena. These implications for understanding correlated materials and developing theoretical frameworks for many-body physics are of crucial importance. Here, we show that a gapless QSL can naturally emerge from a DQCP. Via large-scale tensor network simulations of a square-lattice spin-1/2 frustrated Heisenberg model, both QSL-state and DQCP-type AFM-VBS transitions are observed. By tuning the coupling constants, the AFM-VBS transition vanishes, and instead, a gapless QSL phase gradually develops in between. Remarkably, along the phase boundaries of AFM-QSL and QSL-VBS transitions, we always observe the same correlation-length exponents, ν≈1.0, which is intrinsically different from the one of the DQCP-type transition, indicating new types of universality classes. Our results explicitly demonstrate a new scenario for understanding the emergence of gapless QSL from an underlying DQCP. The discovered QSL phase survives in a large region of tuning parameters, and we expect its experimental realization in solid-state materials or quantum simulators. |
Tuesday, March 7, 2023 2:18PM - 2:30PM |
G56.00015: Non-centrosymmetric magnetism in twisted bilayer CrI3 Kyoung-Min Kim, Do Hun Kiem, Grigory Bednik, Moon Jip Park, Myung Jun Han Twist engineering of van der Waals magnets emerges as a novel platform for manipulating exotic magnetic states. However, the complicated form of spin interactions in the large moiré superlattice obstructs the concrete understanding of such spin systems. To tackle this problem, we developed a generic ab-initio spin Hamiltonian for twisted bilayer magnets for the first time. Our atomistic model reveals several unprecedented features and phases including AB sublattice symmetry breaking and, in turn, skyrmion phase. That is to say, twisting van der Waals magnets introduces a promising route to realize non-centrosymmetric magnetism. |
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