  The S = 1/2 triangular lattice antiferromagnet (TLAF) stands out as 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 deg order below TN = 3.26 K. The spin Hamiltonian was determined
by fitting the energy-resolved paramagnetic excitations measured at T > TN,
revealing an exceptionally strong easy-plane XXZ exchange anisotropy. Below TN,
the excitation spectrum exhibits a high energy continuum having a larger
spectral weight than the single-magnon modes. Combined with advanced
theoretical calculations of magnetic excitations based on magnons and spinons,
this observation suggests a scenario characterized by a spinon confinement
length that markedly exceeds the lattice spacing. We conjecture that this
phenomenon arises due to the proximity to a quantum melting point, which
persists even in the presence of 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 and
are 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.
