Dichotomy in temporal and thermal spin correlations observed in the breathing pyrochlore LiGa1−xInxCr4O8

AbstractA breathing pyrochlore system is predicted to host a variety of quantum spin liquids. Despite tremendous experimental and theoretical efforts, such sought-after states remain elusive as perturbation terms and lattice distortions lead to magnetic order. Here, we utilize bond alternation and disorder to tune a magnetic ground state in the Cr-based breathing pyrochlore LiGa1−xInxCr4O8. By combining thermodynamic and magnetic resonance techniques, we provide experimental signatures of a spin-liquid-like state in x = 0.8, namely, a nearly T2-dependent magnetic specific heat and persistent spin dynamics by muon spin relaxation (μSR). Moreover, 7Li NMR, ZF-μSR, and ESR unveil the temporal and thermal dichotomy of spin correlations: a tetramer singlet on a slow time scale vs. a spin-liquid-like state on a fast time scale. Our results showcase that a bond disorder in the breathing pyrochlore offers a promising route to disclose exotic magnetic phases.

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Emergent spin-liquid-like state in the bond-disordered breathing pyrochlore

10.21203/rs.3.rs-50493/v1 ◽

2020 ◽

Author(s):

Suheon Lee ◽

Seunghwan Do ◽

W.-J. Lee ◽

Y.-S. Choi ◽

Johan Van Tol ◽

...

Keyword(s):

Nearest Neighbor ◽

Spin Dynamics ◽

Muon Spin ◽

Quantum Spin ◽

Spin Fluctuations ◽

Spin Liquid ◽

Spin Liquids ◽

Magnetic Ground State ◽

Magnetic Specific Heat ◽

State Of Matter

Abstract A breathing pyrochlore system is predicted to host a variety of quantum spin liquids. However, perturbations beyond nearest-neighbor Heisenberg interaction are an obstacle to identifying such exotic states. Here, we utilize a bond-alternating disorder to tune a magnetic ground state in the Cr-based breathing pyrochlore. By combining thermodynamic and magnetic resonance techniques, we provide experimental signatures of a spin-liquid-like state in LiGa1-xInxCr4O8 (x=0.2), namely, a nearly T2-dependent magnetic specific heat and a persistent spin dynamics by muon spin relaxation (μSR). Moreover, 7Li NMR, ZF-μSR, and ESR unveil the dichotomic nature of both temporal and thermal spin fluctuations: slowly fluctuating tetramer singlets at high temperatures and a fast fluctuating spin-liquid-like state at low temperatures. Our results suggest that a bond disorder in the breathing pyrochlore offers a new route to achieve an unexplored state of matter.

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Quantum phases and spin liquid properties of 1T-TaS2

npj Quantum Materials ◽

10.1038/s41535-021-00367-w ◽

2021 ◽

Vol 6 (1) ◽

Author(s):

Samuel Mañas-Valero ◽

Benjamin M. Huddart ◽

Tom Lancaster ◽

Eugenio Coronado ◽

Francis L. Pratt

Keyword(s):

Muon Spin ◽

Density Wave ◽

Wave Structure ◽

Quantum Spin ◽

Spin Liquid ◽

Topological Order ◽

Spin Liquids ◽

Temperature Dependent ◽

Quantum Phases ◽

Frustrated Spin

AbstractQuantum materials exhibiting magnetic frustration are connected to diverse phenomena, including high Tc superconductivity, topological order, and quantum spin liquids (QSLs). A QSL is a quantum phase (QP) related to a quantum-entangled fluid-like state of matter. Previous experiments on QSL candidate materials are usually interpreted in terms of a single QP, although theories indicate that many distinct QPs are closely competing in typical frustrated spin models. Here we report on combined temperature-dependent muon spin relaxation and specific heat measurements for the triangular-lattice QSL candidate material 1T-TaS2 that provide evidence for competing QPs. The measured properties are assigned to arrays of individual QSL layers within the layered charge density wave structure of 1T-TaS2 and their characteristic parameters can be interpreted as those of distinct Z2 QSL phases. The present results reveal that a QSL description can extend beyond the lowest temperatures, offering an additional perspective in the search for such materials.

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

Nature Communications ◽

10.1038/s41467-021-21495-8 ◽

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.

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Survival of itinerant excitations and quantum spin state transitions in YbMgGaO4 with chemical disorder

Nature Communications ◽

10.1038/s41467-021-25247-6 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

X. Rao ◽

G. Hussain ◽

Q. Huang ◽

W. J. Chu ◽

N. Li ◽

...

Keyword(s):

Spin State ◽

Magnetic Ordering ◽

Temperature Limit ◽

Quantum Spin ◽

Spin Fluctuations ◽

State Transitions ◽

Spin Liquid ◽

Magnetic Ground State ◽

Effective Spin ◽

Ideal System

AbstractA recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state. The ultimate question is whether the QSL survives disorder or the disorder leads to a “spin-liquid-like” state, such as the proposed random-singlet (RS) state. Since disorder is a standard feature of most QSL candidates, this question represents a major challenge for QSL candidates. YbMgGaO4, a triangular lattice antiferromagnet with effective spin-1/2 Yb3+ions, is an ideal system to address this question, since it shows no long-range magnetic ordering with Mg/Ga site disorder. Despite the intensive study, it remains unresolved as to whether YbMgGaO4 is a QSL or in the RS state. Here, through ultralow-temperature thermal conductivity and magnetic torque measurements, plus specific heat and DC magnetization data, we observed a residual κ0/T term and series of quantum spin state transitions in the zero temperature limit for YbMgGaO4. These observations strongly suggest that a QSL state with itinerant excitations and quantum spin fluctuations survives disorder in YbMgGaO4.

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

Science Advances ◽

10.1126/sciadv.aat5535 ◽

2018 ◽

Vol 4 (11) ◽

pp. eaat5535 ◽

Cited By ~ 10

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.

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Magnetic field-induced intermediate quantum spin liquid with a spinon Fermi surface

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1821406116 ◽

2019 ◽

Vol 116 (25) ◽

pp. 12199-12203 ◽

Cited By ~ 18

Author(s):

Niravkumar D. Patel ◽

Nandini Trivedi

Keyword(s):

Magnetic Field ◽

Fermi Surface ◽

Intermediate Phase ◽

Quantum Spin ◽

Spin Liquid ◽

Spin Correlations ◽

Density Matrix Renormalization ◽

Static Spin ◽

Kitaev Model ◽

Quantum Spin Liquid

The Kitaev model with an applied magnetic field in the H∥[111] direction shows two transitions: from a nonabelian gapped quantum spin liquid (QSL) to a gapless QSL at Hc1≃0.2K and a second transition at a higher field Hc2≃0.35K to a gapped partially polarized phase, where K is the strength of the Kitaev exchange interaction. We identify the intermediate phase to be a gapless U(1) QSL and determine the spin structure function S(k) and the Fermi surface ϵFS(k) of the gapless spinons using the density matrix renormalization group (DMRG) method for large honeycomb clusters. Further calculations of static spin-spin correlations, magnetization, spin susceptibility, and finite temperature-specific heat and entropy corroborate the gapped and gapless nature of the different field-dependent phases. In the intermediate phase, the spin-spin correlations decay as a power law with distance, indicative of a gapless phase.

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Observation of plaquette fluctuations in the spin-1/2 honeycomb lattice

npj Quantum Materials ◽

10.1038/s41535-020-00287-1 ◽

2020 ◽

Vol 5 (1) ◽

Author(s):

Christian Wessler ◽

Bertrand Roessli ◽

Karl W. Krämer ◽

Bernard Delley ◽

Oliver Waldmann ◽

...

Keyword(s):

Quantum Critical Point ◽

Spin Correlation ◽

Quantum Spin ◽

Honeycomb Lattice ◽

Spin Liquids ◽

Spin Correlations ◽

Quantum Spin Liquids ◽

Dynamic Spin ◽

New Perspective ◽

The Continuum

AbstractQuantum spin liquids are materials that feature quantum entangled spin correlations and avoid magnetic long-range order at T = 0 K. Particularly interesting are two-dimensional honeycomb spin lattices where a plethora of exotic quantum spin liquids have been predicted. Here, we experimentally study an effective S = 1/2 Heisenberg honeycomb lattice with competing nearest and next-nearest-neighbour interactions. We demonstrate that YbBr3 avoids order down to at least T = 100 mK and features a dynamic spin–spin correlation function with broad continuum scattering typical of quantum spin liquids near a quantum critical point. The continuum in the spin spectrum is consistent with plaquette type fluctuations predicted by theory. Our study is the experimental demonstration that strong quantum fluctuations can exist on the honeycomb lattice even in the absence of Kitaev-type interactions, and opens a new perspective on quantum spin liquids.

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2000188117 ◽

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.

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

Nature Communications ◽

10.1038/s41467-020-20562-w ◽

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.

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