Field-Induced Spin Dynamics of the S = 1/2 Triangular-Lattice Antiferromagnet CsYbSe₂

Geometrically frustrated magnets provide an intriguing playground for investigation of novel phenomena in condensed matter physics. Strong magnetic frustration may produce large degeneracy of the ground state and prevent formation of magnetic order in favor of exotic states such as quantum spin-liquid or spin-ice phases. The two-dimensional (2D) triangular-lattice antiferromagnet is a prototypical example of a frustrated antiferromagnet, and thus is a good platform to explore potential quantum spin-liquid behavior. We will present the recent in-field neutron scattering study examining a 2D spin-1/2 triangular-lattice antiferromagnet, CsYbSe₂, which is a member of the large family of rare-earth chalcogenide quantum spin liquid candidates. The inelastic neutron scattering spectra evolve from highly damped continuum-like excitations at zero field to relatively sharp spin wave modes in the field-induced up-up-down phase. The density-matrix renormalization group calculations with a Heisenberg triangular-lattice nearest-neighbor antiferromagnetic model reproduce the essential features of the experimental spectra, including continuum-like excitations at zero field, a series of sharp magnons in the up-up-down phase as well as higher energy two-magnon excitations. This work presents a comprehensive experimental and theoretical overview of the unconventional field-induced spin dynamics in triangular-lattice Heisenberg antiferromagnets.