scholarly journals Spin liquid and ferroelectricity close to a quantum critical point in PbCuTe2O6

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Christian Thurn ◽  
Paul Eibisch ◽  
Arif Ata ◽  
Maximilian Winkler ◽  
Peter Lunkenheimer ◽  
...  
Keyword(s):  
Quantum Critical Point ◽  
Quantum Fluctuations ◽  
Quantum Spin ◽  
Spin Liquid ◽  
Spin Liquids ◽  
Range Magnetic Order ◽  
Powder Samples ◽  
Quantum Critical ◽  
Quantum Spin Liquid ◽  
Long Range Magnetic Order

AbstractGeometrical frustration among interacting spins combined with strong quantum fluctuations destabilize long-range magnetic order in favor of more exotic states such as spin liquids. By following this guiding principle, a number of spin liquid candidate systems were identified in quasi-two-dimensional (quasi-2D) systems. For 3D, however, the situation is less favorable as quantum fluctuations are reduced and competing states become more relevant. Here we report a comprehensive study of thermodynamic, magnetic and dielectric properties on single crystalline and pressed-powder samples of PbCuTe2O6, a candidate material for a 3D frustrated quantum spin liquid featuring a hyperkagome lattice. Whereas the low-temperature properties of the powder samples are consistent with the recently proposed quantum spin liquid state, an even more exotic behavior is revealed for the single crystals. These crystals show ferroelectric order at TFE ≈ 1 K, accompanied by strong lattice distortions, and a modified magnetic response—still consistent with a quantum spin liquid—but with clear indications for quantum critical behavior.

scholarly journals From magnetic order to quantum disorder in the Zn-barlowite series of S = 1/2 kagomé antiferromagnets

2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Katherine Tustain ◽  
Brendan Ward-O’Brien ◽  
Fabrice Bert ◽  
Tianheng Han ◽  
Hubertus Luetkens ◽  
...  
Keyword(s):  
Long Range ◽  
Ground State ◽  
Density Functional ◽  
Magnetic Order ◽  
Parent Compound ◽  
Quantum Spin ◽  
Spin Liquid ◽  
Range Magnetic Order ◽  
Quantum Spin Liquid ◽  
Long Range Magnetic Order

Abstract We report a comprehensive muon spectroscopy study of the Zn-barlowite series of $$S=\frac{1}{2}$$ S = 1 2 kagomé antiferromagnets, ZnxCu4−x(OH)6FBr, for x = 0.00 to 0.99(1). By combining muon spin relaxation and rotation measurements with state-of-the-art density-functional theory muon-site calculations, we observe the formation of both μ–F and μ–OH complexes in Zn-barlowite. From these stopping sites, implanted muon spins reveal the suppression of long-range magnetic order into a possible quantum spin liquid state upon the increasing concentration of Zn-substitution. In the parent compound (x = 0), static long-range magnetic order below TN = 15 K manifests itself in the form of spontaneous oscillations in the time-dependent muon asymmetry signal consistent with the dipolar fields expected from the calculated muon stopping sites and the previously determined magnetic structure of barlowite. Meanwhile, in the x = 1.0 end-member of the series—in which antiferromagnetic kagomé layers of Cu2+$$S=\frac{1}{2}$$ S = 1 2 moments are decoupled by diamagnetic Zn2+ ions—we observe that dynamic magnetic moment fluctuations persist down to at least 50 mK, indicative of a quantum disordered ground state. We demonstrate that this crossover from a static to dynamic magnetic ground state occurs for compositions of Zn-barlowite with x > 0.5, which bears resemblance to the dynamical behaviour of the widely studied Zn-paratacamite series that contains the quantum spin liquid candidate herbertsmithite.

scholarly journals Giant isotropic magneto-thermal conductivity of metallic spin liquid candidate Pr2Ir2O7 with quantum criticality

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
J. M. Ni ◽  
Y. Y. Huang ◽  
E. J. Cheng ◽  
Y. J. Yu ◽  
B. L. Pan ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Critical Point ◽  
Quantum Critical Point ◽  
Magnetic Monopoles ◽  
Quantum Criticality ◽  
Quantum Spin ◽  
Spin Liquid ◽  
Zero Field ◽  
Spin Liquids ◽  
Quantum Critical

AbstractSpin liquids are exotic states with no spontaneous symmetry breaking down to zero-temperature because of the highly entangled and fluctuating spins in frustrated systems. Exotic excitations like magnetic monopoles, visons, and photons may emerge from quantum spin ice states, a special kind of spin liquids in pyrochlore lattices. These materials usually are insulators, with an exception of the pyrochlore iridate Pr2Ir2O7, which was proposed as a metallic spin liquid located at a zero-field quantum critical point. Here we report the ultralow-temperature thermal conductivity measurements on Pr2Ir2O7. The Wiedemann–Franz law is verified at high fields and inferred at zero field, suggesting no breakdown of Landau quasiparticles at the quantum critical point, and the absence of mobile fermionic excitations. This result puts strong constraints on the description of the quantum criticality in Pr2Ir2O7. Unexpectedly, although the specific heats are anisotropic with respect to magnetic field directions, the thermal conductivities display the giant but isotropic response. This indicates that quadrupolar interactions and quantum fluctuations are important, which will help determine the true ground state of this material.

scholarly journals Correlation holes and slow dynamics induced by fractional statistics in gapped quantum spin liquids

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Oliver Hart ◽  
Yuan Wan ◽  
Claudio Castelnovo
Keyword(s):  
Transport Properties ◽  
Realistic Model ◽  
Feedback Mechanism ◽  
Quantum Spin ◽  
Spin Liquid ◽  
Spin Liquids ◽  
Slow Dynamics ◽  
Temperature Dependent ◽  
Quantum Spin Liquids ◽  
Quantum Spin Liquid

AbstractRealistic model Hamiltonians for quantum spin liquids frequently exhibit a large separation of energy scales between their elementary excitations. At intermediate, experimentally relevant temperatures, some excitations are sparse and hop coherently, whereas others are thermally incoherent and dense. Here, we study the interplay of two such species of quasiparticle, dubbed spinons and visons, which are subject to nontrivial mutual statistics – one of the hallmarks of quantum spin liquid behaviour. Our results for $${{\mathbb{Z}}}_{2}$$ Z 2 quantum spin liquids show an intriguing feedback mechanism, akin to the Nagaoka effect, whereby spinons become localised on temperature-dependent patches of expelled visons. This phenomenon has important consequences for the thermodynamic and transport properties of the system, as well as for its response to quenches in temperature. We argue that these effects can be measured in experiments and may provide viable avenues for obtaining signatures of quantum spin liquid behaviour.

scholarly journals Entanglement signatures of emergent Dirac fermions: Kagome spin liquid and quantum criticality

2018 ◽  
Vol 4 (11) ◽  
pp. eaat5535 ◽  
Author(s):  
Wei Zhu ◽  
Xiao Chen ◽  
Yin-Chen He ◽  
William Witczak-Krempa
Keyword(s):  
Entanglement Entropy ◽  
Quantum Critical Point ◽  
Quantum Spin ◽  
Spin Liquid ◽  
Dirac Fermions ◽  
Spin Liquids ◽  
Density Matrix Renormalization ◽  
Dirac Semimetal ◽  
A Charge ◽  
Aharonov Bohm

Quantum spin liquids (QSLs) are exotic phases of matter that host fractionalized excitations. It is difficult for local probes to characterize QSL, whereas quantum entanglement can serve as a powerful diagnostic tool due to its nonlocality. The kagome antiferromagnetic Heisenberg model is one of the most studied and experimentally relevant models for QSL, but its solution remains under debate. Here, we perform a numerical Aharonov-Bohm experiment on this model and uncover universal features of the entanglement entropy. By means of the density matrix renormalization group, we reveal the entanglement signatures of emergent Dirac spinons, which are the fractionalized excitations of the QSL. This scheme provides qualitative insights into the nature of kagome QSL and can be used to study other quantum states of matter. As a concrete example, we also benchmark our methods on an interacting quantum critical point between a Dirac semimetal and a charge-ordered phase.

scholarly journals Quantum spin-liquid states in an organic magnetic layer and molecular rotor hybrid

2020 ◽  
Vol 117 (47) ◽  
pp. 29555-29560
Author(s):  
Péter Szirmai ◽  
Cécile Mézière ◽  
Guillaume Bastien ◽  
Pawel Wzietek ◽  
Patrick Batail ◽  
...  
Keyword(s):  
Magnetic Measurements ◽  
Magnetic Layer ◽  
Quantum Spin ◽  
Spin Liquid ◽  
Organic Crystals ◽  
Spin Liquids ◽  
Molecular Rotor ◽  
Low Dimensionality ◽  
Liquid States ◽  
Quantum Spin Liquid

The exotic properties of quantum spin liquids (QSLs) have continually been of interest since Anderson’s 1973 ground-breaking idea. Geometrical frustration, quantum fluctuations, and low dimensionality are the most often evoked material’s characteristics that favor the long-range fluctuating spin state without freezing into an ordered magnet or a spin glass at low temperatures. Among the few known QSL candidates, organic crystals have the advantage of having rich chemistry capable of finely tuning their microscopic parameters. Here, we demonstrate the emergence of a QSL state in [EDT-TTF-CONH2]2+[BABCO−] (EDT-BCO), where the EDT molecules with spin-1/2 on a triangular lattice form layers which are separated by a sublattice of BCO molecular rotors. By several magnetic measurements, we show that the subtle random potential of frozen BCO Brownian rotors suppresses magnetic order down to the lowest temperatures. Our study identifies the relevance of disorder in the stabilization of QSLs.

scholarly journals Linear resistivity and Sachdev-Ye-Kitaev (SYK) spin liquid behavior in a quantum critical metal with spin-1/2 fermions

2020 ◽  
Vol 117 (31) ◽  
pp. 18341-18346 ◽  
Author(s):  
Peter Cha ◽  
Nils Wentzell ◽  
Olivier Parcollet ◽  
Antoine Georges ◽  
Eun-Ah Kim
Keyword(s):  
Fermi Liquid ◽  
Spin Dynamics ◽  
Quantum Critical Point ◽  
Quantum Spin ◽  
Spin Interaction ◽  
Spin Liquid ◽  
Spin Glass Phase ◽  
Scattering Rate ◽  
Liquid Behavior ◽  
Quantum Critical

“Strange metals” with resistivity depending linearly on temperature T down to low T have been a long-standing puzzle in condensed matter physics. Here, we consider a lattice model of itinerant spin-1/2fermions interacting via onsite Hubbard interaction and random infinite-ranged spin–spin interaction. We show that the quantum critical point associated with the melting of the spin-glass phase by charge fluctuations displays non-Fermi liquid behavior, with local spin dynamics identical to that of the Sachdev-Ye-Kitaev family of models. This extends the quantum spin liquid dynamics previously established in the large-M limit ofSU(M)symmetric models to models with physicalSU(2)spin-1/2electrons. Remarkably, the quantum critical regime also features a Planckian linear-T resistivity associated with a T-linear scattering rate and a frequency dependence of the electronic self-energy consistent with the marginal Fermi liquid phenomenology.

scholarly journals Quantum spin liquids

Science ◽  
2020 ◽  
Vol 367 (6475) ◽  
pp. eaay0668 ◽  
Author(s):  
C. Broholm ◽  
R. J. Cava ◽  
S. A. Kivelson ◽  
D. G. Nocera ◽  
M. R. Norman ◽  
...  
Keyword(s):  
Ground State ◽  
Quantum Spin ◽  
Spin Liquid ◽  
Spin Liquids ◽  
Quantum Phases ◽  
Quantum Spin Liquids ◽  
The Past ◽  
Quantum Spin Liquid ◽  
Single Material ◽  
Topological Character

Spin liquids are quantum phases of matter with a variety of unusual features arising from their topological character, including “fractionalization”—elementary excitations that behave as fractions of an electron. Although there is not yet universally accepted experimental evidence that establishes that any single material has a spin liquid ground state, in the past few years a number of materials have been shown to exhibit distinctive properties that are expected of a quantum spin liquid. Here, we review theoretical and experimental progress in this area.

scholarly journals Strong quantum fluctuations in a quantum spin liquid candidate with a Co-based triangular lattice

2019 ◽  
Vol 116 (29) ◽  
pp. 14505-14510 ◽  
Author(s):  
Ruidan Zhong ◽  
Shu Guo ◽  
Guangyong Xu ◽  
Zhijun Xu ◽  
Robert J. Cava
Keyword(s):  
Triangular Lattice ◽  
Magnetic Ordering ◽  
Quantum Fluctuations ◽  
Quantum Spin ◽  
Low Energy ◽  
Spin Liquid ◽  
Effective Spin ◽  
Experimental Realization ◽  
Quantum Spin Liquid ◽  
Applied Fields

Currently under active study in condensed matter physics, both theoretically and experimentally, are quantum spin liquid (QSL) states, in which no long-range magnetic ordering appears at low temperatures due to strong quantum fluctuations of the magnetic moments. The existing QSL candidates all have their intrinsic disadvantages, however, and solid evidence for quantum fluctuations is scarce. Here, we report a previously unreported compound, Na2BaCo(PO4)2, a geometrically frustrated system with effective spin-1/2 local moments for Co2+ ions on an isotropic 2-dimensional (2D) triangular lattice. Magnetic susceptibility and neutron scattering experiments show no magnetic ordering down to 0.05 K. Thermodynamic measurements show that there is a tremendous amount of magnetic entropy present below 1 K in 0-applied magnetic field. The presence of localized low-energy spin fluctuations is revealed by inelastic neutron measurements. At low applied fields, these spin excitations are confined to low energy and contribute to the anomalously large specific heat. In larger applied fields, the system reverts to normal behavior as evident by both neutron and thermodynamic results. Our experimental characterization thus reveals that this material is an excellent candidate for the experimental realization of a QSL state.

scholarly journals Discovery of an ultra-quantum spin liquid

2021 ◽  
Author(s):  
Yanxing Yang ◽  
Cheng Tan ◽  
Zihao Zhu ◽  
J. Zhang ◽  
Zhaofeng Ding ◽  
...  
Keyword(s):  
Specific Heat ◽  
Quantum Fluctuations ◽  
Quantum Spin ◽  
Spin Liquid ◽  
Singlet Ground State ◽  
Relaxation Rates ◽  
Scale Invariant ◽  
Liquid States ◽  
Increasing Temperature ◽  
Quantum Spin Liquid

Abstract Quantum fluctuations are expected to lead to highly entangled spin-liquid states in some two-dimensional spin-1/2 compounds. We have synthesized and measured thermodynamic properties and muon relaxation rates in two related such compounds, one of which is the least disordered of this kind synthesized hitherto and reveals intrinsic properties of a class of spin-liquids. Its measured properties can all be simply characterized by scale invariant time-dependent fluctuations with a single parameter. The specific heat divided by temperature and muon relaxation rates are both temperature independent at low temperatures, followed by a logarithmic decrease with increasing temperature. Even more remarkably, ∼57% of the magnetic entropy is missing down to temperatures of O(10−3) the exchange energy, independent of magnetic field up to gµBH > kBT . This is evidence that quantum fluctuations lead either to a gigantic specific heat peak from topological singlet excitations below such temperatures, or to an extensively degenerate topological singlet ground state. These results reveal an ultra-quantum state of matter.

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