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arXiv · 1111.5406

Higgs transition from a magnetic Coulomb liquid to a ferromagnet in Yb_2Ti_2O_7

Lieh-Jeng Chang·Shigeki Onoda·Yixi Su·Ying-Jer Kao·Ku-Ding Tsuei·Yukio Yasui·Kazuhisa Kakurai·Martin Richard Lees
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Abstract

In a class of frustrated magnets known as spin ice, magnetic monopoles emerge as classical defects and interact via the magnetic Coulomb law. With quantum-mechanical interactions, these magnetic charges are carried by fractionalised bosonic quasi-particles, spinons, which can undergo Bose-Einstein condensation through a first-order transition via the Higgs mechanism. Here, we report evidence of a Higgs transition from a magnetic Coulomb liquid to a ferromagnet in single-crystal Yb2Ti2O7. Polarised neutron-scattering experiments show that the diffuse [111]-rod scattering and pinch-point features which develop on cooling are suddenly suppressed below T_C ~ 0.21 K, where magnetic Bragg peaks and a full depolarisation of the neutron spins are observed with thermal hysteresis, indicating a first-order ferromagnetic transition. Our results are explained on the basis of a quantum spin-ice model, whose high-temperature phase is effectively described as a magnetic Coulomb liquid, while the ground state shows a nearly collinear ferromagnetism with gapped spin excitations.

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Lieh-Jeng Chang, Shigeki Onoda, Yixi Su, Ying-Jer Kao, Ku-Ding Tsuei, Yukio Yasui, Kazuhisa Kakurai, Martin Richard Lees. 2011-11-23. Higgs transition from a magnetic Coulomb liquid to a ferromagnet in Yb_2Ti_2O_7. https://doi.org/10.1038/ncomms1989

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