Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B64: Quantum Spin LiquidsRecordings Available
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Sponsoring Units: DCMP Chair: Matthew Enjalran, Southern Conn State Univ Room: Hyatt Regency Hotel -Grant Park B |
Monday, March 14, 2022 11:30AM - 11:42AM |
B64.00001: Spin response and magnetic absorption of Kitaev quantum liquids under an external field Shi Feng, Nandini Trivedi Quantum spin liquids (QSL) are novel quantum many-body systems that do not order down to zero temperature and harbor topological phases with fractionalized excitations. The Kitaev QSL on a honeycomb lattice has gapped spin excitations and extremely short-ranged spin correlations due to conserved Z2 fluxes which governs its spin response. In the linear response regime, we explore the frequency resolved spin response and magnetic absorption of Kitaev model as a function of temperature by varying the bond strengths away from the isotropic point and by applying an out-of-plane magnetic field. The evolution of the spin response reflects the interplay between itinerant majoranas and dynamical Z2 fluxes. Our results can be measured by microwave and terahertz spectroscopies. We also make predictions of spin relaxation phenomena that can be detected by pump-probe experiment. |
Monday, March 14, 2022 11:42AM - 11:54AM |
B64.00002: Spinons and Damped Phonons in Spin-1/2 Quantum-Liquid Ba4Ir3O10 Observed by Raman Scattering Aaron Sokolik, Sami Hakani, Nick Pellatz, Susmita Roy, Dmitry Reznik, Gang Cao, Itamar Kimchi, Hengdi Zhao In spin-1/2 Mott insulators, non-magnetic quantum spin liquid phases are often argued to arise when the system shows no magnetic ordering, but identifying positive signatures of these phases or related spinon quasiparticles can be elusive. Here we use Raman scattering to provide three signatures for spinons in a possible spin-orbit quantum liquid material Ba4Ir3O10: (1) A broad hump, which we show can arise from Luttinger Liquid spinons in Raman with parallel photon polarizations normal to 1D chains; (2) Strong phonon damping from phonon-spin coupling via the spin-orbit interaction; and (3) the absence of (1) and (2) in the Neel ordered phase of the same compound where 2% of Ba is substituted by Sr. The phonon damping via itinerant spinons in this quantum-liquid insulator suggests a new mechanism for enhancing thermoelectricity in strongly correlated conductors, through a neutral quantum liquid that does not affect electronic transport. |
Monday, March 14, 2022 11:54AM - 12:06PM |
B64.00003: Raman response via 4-spinon continuum in spin-1/2 quantum liquid Ba4Ir3O10 Sami Hakani, Aaron Sokolik, Nick Pellatz, Susmita Roy, Itamar Kimchi, Gang Cao, Dmitry Reznik Spin-1/2 magnetic insulators can avoid ordered phases by forming a quantum liquid (QL) state. But beyond lack of ordering, positive signatures of QL states are difficult to access. Ba4Ir3O10 is a recently discovered Seff = 1/2 insulator with no magnetic order down to 0.2 K despite strong antiferromagnetic interactions TCW = 100-700 K. Here, I report on experimental results and our theoretical analysis of inelastic Raman scattering measurements on Ba4Ir3O10 which find broadened phonon peaks superposed on a large bandwidth hump feature. Adding disorder via 2% Ba-to-Sr substitution produces magnetic order while also eliminating the hump feature below TNSr = 130 K, suggesting the hump arises from spin excitations in a fragile QL. We employ a model of free 1D spinons to compute the 4-spinon Raman response, finding agreement with experiment across two different mean field limits. For photon polarizations used experimentally, a nonvanishing Raman response requires both frustrated second neighbor couplings and zig-zagged spin chains, as indeed appear in Ba4Ir3O10. Together with other signatures such as phonon broadening from spin-orbit-coupled-spinon scattering, the analysis suggests a fragile QL state with gapless spinon excitations in Ba4Ir3O10. |
Monday, March 14, 2022 12:06PM - 12:18PM |
B64.00004: Quantum spin-glass criticality in disordered frustrated dimer magnets Darshan G Joshi, Matthias Vojta
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Monday, March 14, 2022 12:18PM - 12:30PM |
B64.00005: Floquet engineering of Kitaev quantum magnets Shizeng Lin, Umesh Kumar, Saikat Banerjee Ultrafast light-matter interaction offers opportunities to control the physical properties of quantum materials. We apply this concept to the Kiteav quantum magnets such as RuCl3 and irridates. These quantum magnets are promising candidates for the realization of the Kiteav quantum spin liquid which hosts highly nontrivial fractionalized excitations. However, the realistic spin Hamiltonian for these materials includes terms that can perturb the system aways from the long-sought for the quantum spin liquid phase. In this work, we propose to use light to tune magnetic interactions in spin-orbit coupled Mott insulators relevant for Kiteav quantum magnets. We derive an effective spin Hamiltonian from multiple orbital spin-orbital coupled Hubbard model coupled to a circularly polarized light using the Floquet theory. We demonstrate that magnetic interactions favorite for quantum spin liquid can be achieved by tuning the frequency and amplitude of the light. Furthermore, an effective Zeeman field is generated by the light due to the inverse Faraday effect. Our work points to a promising route to stabilize quantum spin liquid by coupling quantum magnets to light. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B64.00006: Thermal Conductivity Measurements of a Quantum Spin Liquid Candidate Luke Pritchard Cairns, James G Analytis In the vast majority of materials that host strongly interacting localised moments, long-range magnetic order will be established at some finite temperature. However, if this long-range order is suppressed by - for example - geometric frustration, a theorised quantum spin liquid (QSL) state might instead emerge. This is a phase of matter characterised by the long-range quantum entanglement of localised moments, which can in some cases give rise to fractionalised, dispersive excitations. In the material NaYbSe2, pseudospin-1/2 moments are localised at the Yb sites, and so lie geometrically frustrated within effective two-dimensional triangular layers. Previous studies have demonstrated that, at mK temperatures, the material exhibits no long range order, a large finite heat capacity and a two-dimensional spectrum of gapless excitations. These are all hallmarks of a QSL, and the material might therefore be a physical realisation of the QSL state. In this work, we have measured the thermal conductivity of NaYbSe2 at temperatures outside the QSL phase. Our results have interesting implications for the material's QSL candidacy. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B64.00007: Order fractionalization in Kitaev-Kondo model II: Three-dimensional examples Alexei Tsvelik and Piers Coleman Alexei M Tsvelik Continuing from part I, this talk will discuss the anomalous transport and |
Monday, March 14, 2022 12:54PM - 1:06PM |
B64.00008: Renormalization group for quantum critical theories with Harris-marginal disorder Koushik Ganesan, Andrew Lucas, Leo R Radzihovsky We develop a renormalization group for small-amplitude Harris-marginal disorder in otherwise strongly interacting quantum critical theories, focusing on systems that have emergent conformal invariance. Using conformal perturbation theory, we argue that previously proposed random fixed points with Lifshitz scaling in fact flow towards other universal fixed points and that this flow can be captured by a "one-loop calculation". Our approach appears best controlled in theories with only a few operators of low scaling dimensions. In this regime, we compare our predictions for the flow of disorder to holographic models and find complete agreement. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B64.00009: Numerical Computation Of Two-Dimensional Quantum Spin Liquids In A Kagome Lattice Chad E Germany, Bryan K Clark Materials like pyrochlore and herbertsmithite have shown promising evidence of spin liquid behavior in neutron scattering experiments motivating the study of quantum spin liquids on the two dimensional kagome lattice. Spin liquids have previously been identified in multiple Hamiltonians on the kagome lattice including in the Heisenberg limit. It is an interesting question whether these various spin liquids are part of a single connected phase. Answering this question would further identify an additional class of Hamiltonians which support spin liquids as well as accumulate further evidence about the identity of the S= 1/2 kagome Heisenberg antiferromagnet spin liquid. Using numerical calculations we explore if there is a phase transition between these various spin liquids. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B64.00010: Spin-wave theory from the fully polarized vacuum for ferrimagnetic spin-(1/2, S) chains in a magnetic field Rene R Montenegro, Wellington M da Silva We compare the ground-state features of alternating ferrimagnetic chains (1/2, S) with S = 1, 3/2, 2, 5/2 in a magnetic field and the corresponding Holstein-Primakoff bosonic models up to order (s/S)1/2 considering the fully polarized magnetization as the boson vacuum. The single-particle Hamiltonian is the Rice-Mele model with uniform hopping and modified boundaries, while the interactions have a correlated (density-dependent) hopping term and magnon-magnon repulsion. We use density matrix renormalization group calculations to show the quantitative agreement between the results from the spin model and the full bosonic approximation. In particular, we verify the good accordance in the behavior of the edge states, associated with the ferrimagnetic plateau, from the two models. Furthermore, we show that the boundary magnon density strongly depends on the interactions and particle statistics. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B64.00011: Phase diagrams of S= 1/2 Bilayer Models of SU(2) symmetric antiferromagnets Fan Zhang, Nisheeta Desai, Ribhu K Kaul, Wenan Guo We study the T=0 phase diagrams of models of bilayers of S=1/2 square lattices antiferromagnets with SU(2) Heisenberg symmetry that have 2, 4 and 6 spin exchanges. We study two families of models, a traditional bilayer model in which the interlayer interaction is Heisenberg so that the two layers can exchange spin (and energy) with each other making it possible to achieve a simple dimerized liquid like state. The resulting phase diagrams is rich with Neel, valence bond solid and simple dimer phases and both first order and continuous transitions, which we demonstrate our consistent with the conventional Landau theory or order prameters. In a second family of models in which the layers can exchange only energy but no spin (reminiscent of the Ashkin-Teller coupling), the simple dimer state cannot occur. Interestingly, we find that the phase transition between N\'eel and VBS is first order in both the spin-spin and energy-energy coupled models, although they have strikingly distinct finite size scaling behavior. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B64.00012: Phonon anomalies associated with spin reorientation in the Kagome ferromagnet Fe3Sn2 Rudolf U Hackl, Ge He, Leander Peis, Ramona Stumberger, Lilian Prodan, Vladimir Tsurkan, Nico Unglert, Liviu Chioncel, István Kézsmárki We present polarization- and temperature-dependent Raman data for the Kagome ferromagnet Fe3Sn2. Eight out of nine expected phonon modes were identified and analyzed using lattice dynamical calculations. The experimental energies compare well with those from the simulations. The analysis of the line widths indicates relatively strong phonon-phonon coupling in the range 0.1 to 1. The temperature-dependent frequencies of three A1g modes show weak anomalies at approximately 100 K. The linewidths of all phonon modes follow the conventional exponential broadening up to room temperature except for the softest A1g mode. The widthof this mode exhibits a kink close to 100 K and becomes nearly constant for T > 100 K. These features are indicative of a spin reorientation taking place in the temperature range above 100 K which might arise from spin-phonon coupling. The low-energy part of the electronic continuum in Eg symmetry depends strongly on temperature. The possible reasons include particle-hole excitation tracking the resistivity, a spin-dependent gap or spin fluctuations. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B64.00013: Disordered groundstate phase of the SU(N) Heisenberg model with four-column representation Nisheeta Desai, Souvik Kundu, Kedar Damle We study the SU(N) Heisenberg interaction with four column representation on the square lattice. We find that the small-N Néel phase disappears for N ≥ 20, where there is no evidence of any order. This is consistent with the large-N theory which predicts a ``2d AKLT'' state that breaks no symmetries of the Hamiltonian in the bulk. Akin to AKLT state in 1d, this state has unpaired spins at the boundaries which form an SU(N) spin chain along both the x and y edges of the square lattice. We find that this spin chain spontaneously breaks translational symmetry along the four edges and forms a valence bond ordered chain. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B64.00014: Theory of spin-polarized STM for spin liquids Sangjin Lee, Gil Young Cho, Moonju Hong We investigate theoretically the spin-polarized scanning tunneling microscopy as a probe for quantum spin liquids. We calculate the tunneling electric currents for various magnetic states and spin liquids as a function of external magnetic field and magnetization of the spin-polarized tip. From the calculation, we will identify characteristic I-V curves for U(1) and Z2 quantum spin liquids, which can be differentiated from more conventional magnetic states. On top of this, we will also consider a magnetic analogue of the Friedel oscillation induced by a local spin impurity, which may help to identify spinon Fermi surfaces in experimental setups. |
Monday, March 14, 2022 2:18PM - 2:30PM |
B64.00015: Renormalization group analysis of short-range correlations in Shastry-Sutherland model Ahmet Keles, Erhai Zhao We study Shastry-Sutherland model and its generalization using pseudofermion Functional Renormalization Group theory. Quantum material SrCu2 (BO3)2 is a very accurate realization of this model where recent experiments reported evidence of phase transitions from a singlet valence bond ground state to a plaquette valence bond state and later to a long-range ordered antiferromagnetic Neel state under tunable pressure. Earlier numerical studies argued possibility of deconfined quantum criticality versus a gapless spin liquid phase in the vicinity of transition from plaquette singlet to Neel state. We develop renormalization flow equations consistent with underlying coupled plaquettes in this system and solve them numerically for large system sizes. We identify a dimer fixed point in the exactly solvable region and show that FRG accurately describes the well established dimer valence bond to plaquette valence bond transition in agreement with the results of the state-of-the-art numerical techniques. Introducing a correlation function to describe the intermediate phase in terms of vertex functions, we show the plaquette ordered state consistent with DRMG results. In the region between plaquette and Neel states, we find continuous flow down to lowest numerical renormalization scale, peak degeneracy in momentum space, and close competition between two distinct plaquettes suggesting suppression of all long-range as well as short-range singlet orders. By analyzing the correlations in this region we demonstrate that exchange couplings map to J1–J2 Heisenberg model around it maximally frustrated regime supporting the exciting possibility of a quantum paramagnet in a small window. |
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