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

Matthew Stern, Claudio Castelnovo, Roderich Moessner, Vadim Oganesyan, Sarang Gopalakrishnan

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1 Scopus citations

Abstract

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, Phys. Rev. Lett. 123, 067204 (2019)PRLTAO0031-900710.1103/PhysRevLett.123.067204] 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 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.

Original languageEnglish (US)
Article number115114
JournalPhysical Review B
Volume104
Issue number11
DOIs
StatePublished - Sep 15 2021

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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