Spin excitations in the frustrated triangular lattice antiferromagnet NaYbO$_2$

TL;DR

This study uses neutron scattering to explore magnetic excitations and phase transitions in NaYbO$_2$, revealing complex field-induced magnetic phases, quantum fluctuation effects, and detailed crystal electric field characteristics in a frustrated triangular lattice antiferromagnet.

Contribution

It provides the first detailed analysis of magnetic excitations and phase transitions in NaYbO$_2$ under magnetic fields, highlighting quantum fluctuation effects and complex magnetic ordering.

Findings

Identification of the crystal electric field structure and a mixed ground state doublet.

Observation of a first-order phase transition into a noncollinear ordered state.

Detection of strong magnon-magnon interactions within the $up-up-down$ phase.

Abstract

Here we present a neutron scattering-based study of magnetic excitations and magnetic order in NaYbO$_2$ under the application of an external magnetic field. The crystal electric field-split $J = 7/2$ multiplet structure is determined, revealing a mixed $|m_z>$ ground state doublet and is consistent with a recent report Ding et al. [1]. Our measurements further suggest signatures of exchange effects in the crystal field spectrum, manifested by a small splitting in energy of the transition into the first excited doublet. The field-dependence of the low-energy magnetic excitations across the transition from the quantum disordered ground state into the fluctuation-driven ordered regime is analyzed. Signs of a first-order phase transition into a noncollinear ordered state are revealed at the upper-field phase boundary of the ordered regime, and higher order magnon scattering, suggestive of strong magnon-magnon interactions, is resolved within the previously reported $up-up-down$ phase. Our results reveal a complex phase diagram of field-induced order and spin excitations within NaYbO$_2$ and demonstrate the dominant role of quantum fluctuations cross a broad range of fields within its interlayer frustrated triangular lattice.