Direct observation of the Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point

Abstract

Spontaneous symmetry-breaking quantum phase transitions play an essential role in condensed matter physics. The collective excitations in the broken-symmetry phase near the quantum critical point can be characterized by fluctuations of phase and amplitude of the order parameter. The phase oscillations correspond to the massless Nambu$-$Goldstone modes whereas the massive amplitude mode, analogous to the Higgs boson in particle physics, is prone to decay into a pair of low-energy Nambu$-$Goldstone modes in low dimensions. Especially, observation of a Higgs amplitude mode in two dimensions is an outstanding experimental challenge. Here, using the inelastic neutron scattering and applying the bond-operator theory, we directly and unambiguously identify the Higgs amplitude mode in a two-dimensional S=1/2 quantum antiferromagnet C${}_9$H${}_{18}$N${}_2$CuBr${}_4$ near a quantum critical point in two dimensions. Owing to an anisotropic energy gap, it kinematically prevents such decay and the Higgs amplitude mode acquires an infinite lifetime.

12 pages, 4 figures in the main text+3 figures in Supplementary Information

References in corpus (12)

• Amplitude / Higgs Modes in Condensed Matter Physics
• The `Higgs' Amplitude Mode at the Two-Dimensional Superfluid-Mott Insulator Transition
• Quantum Magnets under Pressure: Controlling Elementary Excitations in TlCuCl3
• Fractional excitations in the square-lattice quantum antiferromagnet
• The Higgs Mode in Disordered Superconductors Close to a Quantum Phase Transition
• Quantum and classical criticality in a dimerized quantum antiferromagnet
• Quantum dynamics and entanglement of spins on a square lattice
• The Higgs mode in a two-dimensional superfluid
• Universal Properties of the Higgs Resonance in (2+1)-Dimensional U(1) Critical Systems
• Effect of pressure on the quantum spin ladder material IPA-CuCl3
• Magnetic ordering induced by interladder coupling in the spin-1/2 Heisenberg two-leg ladder antiferromagnet C${}_9$H${}_{18}$N${}_2$CuBr${}_4$
• Neutron scattering study of a quasi-2D spin-1/2 dimer system Piperazinium Hexachlorodicuprate under hydrostatic pressure

Cited by in corpus (14)

• Spinon Confinement and a Sharp Longitudinal Mode in Yb${}_2$Pt${}_2$Pb in Magnetic Fields
• Bulk and edge dynamics of a 2D Affleck-Kennedy-Lieb-Tasaki model
• Chiral and flat-band magnetic cluster excitations in a ferromagnetic kagome metal
• Following the Higgs mode across the BCS-BEC crossover in two dimensions
• The Higgs Mode of Planar Coupled Spin-Ladders and its Observation in C${}_9$H${}_{18}$N${}_2$CuBr${}_4$
• Continuous similarity transformation for critical phenomena: easy-axis antiferromagnetic XXZ model
• Effects of quantum fluctuations on the low-energy collective modes of two-dimensional superfluid Fermi gases from the BCS to the Bose Limit
• Exciton condensation in bilayer spin-orbit insulator
• Chirped amplitude mode in photo-excited superconductors
• Exciting the long-lived Higgs mode in superfluid Fermi gases with particle removal
• A universal pairing gap measurement proposal by dynamical excitations in 2D doped attractive Fermi-Hubbard model with spin-orbit coupling
• Collective excitations in magnetic topological insulators and axion dark matter search
• Total Moment Sum Rule for Magnets in the Vicinity of Quantum Critical Point
• Quantum Quenches of an SO(5) Pseudospin Reveal Higgs Bosons