Spin excitations in the frustrated triangular lattice antiferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>NaYbO</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
Mitchell M. Bordelon, Chunxiao Liu, Lorenzo Posthuma, Paul M. Sarte, N. P. Butch, Daniel M. Pajerowski, Arnab Banerjee, Leon Balents, Stephen D. Wilson
Abstract
Here we present a neutron scattering-based study of magnetic excitations and magnetic order in ${\mathrm{NaYbO}}_{2}$ under the application of an external magnetic field. The crystalline electric field-split $J=7/2$ multiplet structure is determined, revealing a mixed $|{m}_{z}\ensuremath{\rangle}$ ground-state doublet, and is consistent with a recent report by Ding et al. [L. Ding, P. Manuel, S. Bachus, F. Gru\ss{}ler, P. Gegenwart, J. Singleton, R. D. Johnson, H. C. Walker, D. T. Adroja, A. D. Hillier, and A. A. Tsirlin, Phys. Rev. B 100, 144432 (2019)]. 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 ${\mathrm{NaYbO}}_{2}$ and demonstrate the dominant role of quantum fluctuations across a broad range of fields within its interlayer frustrated triangular lattice.