Journal
PHYSICAL REVIEW B
Volume 104, Issue 11, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.104.115114
Keywords
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Funding
- EPSRC [EP/M007065/1, EP/K028960/1] Funding Source: UKRI
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This study investigates the response of quantum spin ice in a specific temperature range, finding that the propagation of monopoles can be transformed into quantum diffusion, with the results being robust and consistent with experimental observations.
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 through an incoherent spin background, taken to be quasistatic on the relevant timescales. The latter introduces well-known blocked directions that we find 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 approximate to 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 wave functions appear to be fractal; we explain this observation via mapping to quantum percolation on trees. The fractal, nonergodic nature of monopole wave functions manifests itself in the low-frequency behavior of monopole spectral functions, and is consistent with experimental observations.
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