Abstract
The fundamental principles of electrodynamics allow an electron carrying both electric monopole (charge) and magnetic dipole (spin) but prohibit its magnetic counterpart. Recently, it was predicted that the magnetic “monopoles” carrying emergent magnetic charges in spin ice systems can induce electric dipoles. The inspiring prediction offers a novel way to study magnetic monopole excitations and magnetoelectric coupling. However, no clear example has been identified up to now. Here, we report the experimental evidence for electric dipoles induced by magnetic monopoles in spin frustrated . The magnetic field applied to pyrochlore along the [111] direction, brings out a “3-in-1-out” magnetic monopole configuration, and then induces a subtle structural phase transition at . The transition is made evident by the nonlinear phonon splitting under magnetic fields and the anomalous crystal-field excitations of ions. The observations consistently point to the displacement of the oxygen anions along the [111] axis which gives rise to the formation of electric dipoles. The finding demonstrates that the scenario of magnetic monopole having both magnetic charge and electric dipole is realized in and sheds light into the coupling between electricity and magnetism of magnetic monopoles in spin frustrated systems.
- Received 29 July 2019
- Accepted 7 February 2020
DOI:https://doi.org/10.1103/PhysRevLett.124.087601
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