Novel Excitations near Quantum Criticality in Geometrically Frustrated Antiferromagnet CsFeCl<sub>3</sub>

The investigation of materials that exhibit quantum phase transition provides valuable insights into fundamental problems in physics. We present neutron scattering under pressure in a triangular-lattice antiferromagnet that has a quantum disorder in the low-pressure phase and a noncollinear structure in the high-pressure phase [1]. The neutron spectrum continuously evolves through critical pressure; a single mode in the disordered state becomes soft with the pressure and it splits into gapless and gapped modes in the ordered phase. Extended spin-wave theory reveals that the longitudinal and transverse fluctuations of spins are hybridized in the modes because of noncollinearity, and novel magnetic excitations are formed. We report a new hybridization of the phase and amplitude fluctuations of the order parameter near a quantum critical point in a spontaneously symmetry-broken state.
[1] S. Hayashida et al., Sci. Adv. 5, eaaw5639 (2019).

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Bulletin of the American Physical Society

APS March Meeting 2020

Volume 65, Number 1

Monday–Friday, March 2–6, 2020; Denver, Colorado

Session B46: Triangular Lattice I

Abstract: B46.00008 : Novel Excitations near Quantum Criticality in Geometrically Frustrated Antiferromagnet CsFeCl3

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Abstract: B46.00008 : Novel Excitations near Quantum Criticality in Geometrically Frustrated Antiferromagnet CsFeCl₃