Field tuning between magnons and excitation continua in a quantum Ising-like triangular antiferromagnet

This proposal is for a continuation experiment on an Ising-like spin-1/2 triangular antiferromagnet where in recent LET measurements we observed a dominant excitation continuum in zero field co-existing with magnetic order Bragg peaks. This is a very surprising result as it suggests anomalously strong quantum fluctuations leading to magnon decay over most of the Brillouin zone. This is in strong contrast to the easy-plane case, where experiments observed sharp magnons throughout reciprocal space with no decay. To understand the origin of the excitation continuum in zero field, whether it is due to magnon decay into multi-magnon continua or more exotic scenarios of magnon fractionalization, we propose to measure how the spectrum evolves into the zero-field continuum starting from the high-field polarized phase, where we have observed sharp, resolution-limited magnons that close gap upon lowering field resulting in magnetic order.