Anomalous continuum scattering and higher-order van Hove singularity in the strongly anisotropic S = 1/2 triangular lattice antiferromagnet

Pyeongjae Park (), E. A. Ghioldi, Andrew F. May, James A. Kolopus, Andrey A. Podlesnyak, Stuart Calder, Joseph A. M. Paddison, A. E. Trumper, L. O. Manuel, Cristian D. Batista, Matthew B. Stone (), Gábor B. Halász () and Andrew D. Christianson ()
Additional contact information
Pyeongjae Park: Oak Ridge National Laboratory
E. A. Ghioldi: University of Tennessee
Andrew F. May: Oak Ridge National Laboratory
James A. Kolopus: Oak Ridge National Laboratory
Andrey A. Podlesnyak: Oak Ridge National Laboratory
Stuart Calder: Oak Ridge National Laboratory
Joseph A. M. Paddison: Oak Ridge National Laboratory
A. E. Trumper: Instituto de Física Rosario (CONICET) and Universidad Nacional de Rosario
L. O. Manuel: Instituto de Física Rosario (CONICET) and Universidad Nacional de Rosario
Cristian D. Batista: University of Tennessee
Matthew B. Stone: Oak Ridge National Laboratory
Gábor B. Halász: Oak Ridge National Laboratory
Andrew D. Christianson: Oak Ridge National Laboratory

Nature Communications, 2024, vol. 15, issue 1, 1-10

Abstract: Abstract The S = 1/2 triangular lattice antiferromagnet (TLAF) is a paradigmatic example of frustrated quantum magnetism. An ongoing challenge involves understanding the influence of exchange anisotropy on the collective behavior within such systems. Using inelastic neutron scattering (INS) and advanced calculation techniques, we have studied the low and high-temperature spin dynamics of Ba2La2CoTe2O12 (BLCTO): a Co2+-based Jeff = 1/2 TLAF that exhibits 120° order below TN = 3.26 K. We determined the spin Hamiltonian by fitting the energy-resolved paramagnetic excitations measured at T > TN, revealing exceptionally strong easy-plane XXZ anisotropy. Below TN, the excitation spectrum exhibits a high energy continuum having a larger spectral weight than the single-magnon modes, suggesting a scenario characterized by a spinon confinement length that markedly exceeds the lattice spacing. We conjecture that this phenomenon arises from the proximity to a quantum melting point, even under strong easy-plane XXZ anisotropy. Finally, we highlight characteristic flat features in the excitation spectrum, which are connected to higher-order van Hove singularities in the magnon dispersion directly induced by easy-plane XXZ anisotropy. Our results provide a rare experimental insight into the nature of highly anisotropic S = 1/2 TLAFs between the Heisenberg and XY limits.

Date: 2024
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DOI: 10.1038/s41467-024-51618-w

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