Collective magnetic Higgs excitation in a pyrochlore ruthenate

Dirk Wulferding, Junkyoung Kim, Mi Kyung Kim, Yang Yang, Jae Hyuck Lee, Dongjoon Song, Dongjin Oh, Heung Sik Kim, Li Ern Chern, Yong Baek Kim, Minji Noh, Hyunyong Choi, Sungkyun Choi, Natalia B. Perkins, Changyoung Kim, Seung Ryong Park

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The emergence of scalar Higgs-type amplitude modes in systems where symmetry is spontaneously broken has been a highly successful, paradigmatic description of phase transitions, with implications ranging from high-energy particle physics to low-energy condensed matter systems. Here, we uncover two successive high temperature phase transitions in the pyrochlore magnet Nd2Ru2O7 at T N = 147 K and T * = 97 K, that lead to giant phonon instabilities and culminate in the emergence of a highly coherent excitation. This coherent excitation, distinct from other phonons and from conventional magnetic modes, stabilizes at a low energy of 3 meV. We assign it to a collective Higgs-type amplitude mode, that involves bond energy modulations of the Ru4 tetrahedra. Its striking two-fold symmetry, incompatible with the underlying crystal structure, highlights the possibility of multiple entangled broken symmetries.

Original languageEnglish (US)
Article number40
Journalnpj Quantum Materials
Issue number1
StatePublished - Dec 2023
Externally publishedYes

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