Correlated Quantum Tunneling of Monopoles in Spin Ice

Tomasello, Bruno; Castelnovo, Claudio; Moessner, Roderich; Quintanilla, Jorge

doi:10.1103/physrevlett.123.067204

Cited by 32 publications

(42 citation statements)

References 37 publications

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“…This quenched randomness affects monopole motion by energetically blocking some directions and, as recently pointed out in Ref. 15, by suppressing the amplitude for certain monopole moves.…”

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confidence: 62%

“…Here, we construct a theory of monopole dynamics in this intermediate temperature regime. The quenched randomness in hopping amplitudes, arising from the random background [15], allows us to draw a connection between the dynamics of spin ice and quantum percolation, and, remarkably, enables more efficient numerical simulations (by only including the parts of Hilbert space that the monopole is allowed to visit by non-vanishing matrix elements in the Hamiltonian). The resulting model is (a) Hierarchy of energy (or equivalently time/temperature) scales in QSI.…”

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confidence: 99%

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Quantum percolation of monopole paths and the response of quantum spin ice

Stern,

Castelnovo,

Moessner

et al. 2019

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We consider quantum spin ice in a temperature regime in which its response is dominated by the coherent motion of a dilute gas of monopoles. The hopping amplitude of a monopole is sensitive to the configuration of its surrounding spins, taken to be quasi-static on the relevant timescales. This leads to well-known blocked directions in the monopole motion; we find that these are sufficient to reduce the coherent propagation of monopoles to quantum diffusion. This result is robust against disorder, as a direct consequence of the ground-state degeneracy, which disrupts the quantum interference processes needed for weak localization. Moreover, recent work [Tomasello et al., Phys. Rev. Lett. 123, 067204 (2019)] has shown that the monopole hopping amplitudes are roughly bimodal: for ≈ 1/3 of the flippable spins surrounding a monopole, these amplitudes are extremely small. We exploit this structure to construct a theory of quantum monopole motion in spin ice. In the limit where the slow hopping terms are set to zero, the monopole wavefunctions appear to be fractal; we explain this observation via a mapping to quantum percolation on trees. The fractal, non-ergodic nature of monopole wavefunctions manifests itself in the low-frequency behavior of monopole spectral functions, and is consistent with experimental observations.

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confidence: 62%

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Quantum percolation of monopole paths and the response of quantum spin ice

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Castelnovo,

Moessner

et al. 2019

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“…On the pyrochlore lattice, an external field cannot be applied transverse to all spins simultaneously because the different local Ising axes are not coplanar, and a homogeneous transverse field that emerges at single-ion level is absent in chemically ordered pyrochlores. However, transverse fields generated by spinspin interactions are related to monopole hopping in spin ice [74], and transverse fields generated by chemical disorder have been identified as a possible route to pyrochlore quantum spin liquid states [14], and used to explain the spin dynamics of Pr 2 Zr 2 O 7 [22,24] and Tb 2 Ti 2 O 7 [75,76]. Nevertheless, a potential challenge to modeling such materials is that chemical disorder generates a broad distribution of transverse fields in the sample [77].…”

Section: Transverse Ising Modelmentioning

confidence: 99%

Quantum Versus Classical Spin Fragmentation in Dipolar Kagome Ice Ho3Mg2Sb3O<

et al. 2020

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A promising route to realize entangled magnetic states combines geometrical frustration with quantumtunneling effects. Spin-ice materials are canonical examples of frustration, and Ising spins in a transverse magnetic field are the simplest many-body model of quantum tunneling. Here, we show that the tripodkagome lattice material Ho 3 Mg 2 Sb 3 O 14 unites an icelike magnetic degeneracy with quantum-tunneling terms generated by an intrinsic splitting of the Ho 3þ ground-state doublet, which is further coupled to a nuclear spin bath. Using neutron scattering and thermodynamic experiments, we observe a symmetrybreaking transition at T Ã ≈ 0.32 K to a remarkable state with three peculiarities: a concurrent recovery of magnetic entropy associated with the strongly coupled electronic and nuclear degrees of freedom; a fragmentation of the spin into periodic and icelike components; and persistent inelastic magnetic excitations down to T ≈ 0.12 K. These observations deviate from expectations of classical spin fragmentation on a kagome lattice, but can be understood within a model of dipolar kagome ice under a homogeneous transverse magnetic field, which we survey with exact diagonalization on small clusters and mean-field calculations. In Ho 3 Mg 2 Sb 3 O 14 , hyperfine interactions dramatically alter the single-ion and collective properties, and suppress possible quantum correlations, rendering the fragmentation with predominantly single-ion quantum fluctuations. Our results highlight the crucial role played by hyperfine interactions in frustrated quantum magnets and motivate further investigations of the role of quantum fluctuations on partially ordered magnetic states.

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“…Altering the environment of a spin may enhance quantum tunnelling between its two Ising states and thus change its dynamical response [36][37][38]. It has been theoretically proposed for Tb 2 Ti 2 O 7 , an Ising pyrochlore with physics less understood than spin ice [39], that a tetragonal distortion can lead to faster dynamics [38]; this, together with the susceptibility of the non-Kramers HTO ground state doublet to transverse fields [37] might give the dynamics of HTO a high sensitivity to uniaxial pressure. Figure 4 shows χ AC at f = 1117.7Hz and B = 0, as a function of temperature for different compressive strains.…”

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Dynamics and thermodynamics of a topological transition in spin ice materials under strain

Pili,

Steppke,

Barber

et al. 2021

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We study single crystals of Dy2Ti2O7 and Ho2Ti2O7 under magnetic field and stress applied along their [001] direction. We find that many of the features that the emergent gauge field of spin ice confers to the macroscopic magnetic properties are preserved in spite of the finite temperature. The magnetisation vs. field shows an upward convexity within a broad range of fields, while the static and dynamic susceptibilities present a peculiar peak. Following this feature for both compounds, we determine a single experimental transition curve: that for the Kasteleyn transition in three dimensions, proposed more than a decade ago. Additionally, we observe that compression up to −0.8% along [001] does not significantly change the thermodynamics. However, the dynamical response of Ho2Ti2O7 is quite sensitive to changes introduced in the Ho 3+ environment. Uniaxial compression can thus open up experimental access to equilibrium properties of spin ice at low temperatures.

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Correlated Quantum Tunneling of Monopoles in Spin Ice

Cited by 32 publications

References 37 publications

Quantum percolation of monopole paths and the response of quantum spin ice

Quantum percolation of monopole paths and the response of quantum spin ice

Quantum Versus Classical Spin Fragmentation in Dipolar Kagome Ice Ho3Mg2Sb3O<

Dynamics and thermodynamics of a topological transition in spin ice materials under strain

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