Abstract.
Cs2CuCl4 is a 2D frustrated quantum magnet that has recently been shown to display a very unusual quantum spin liquid state. The excitations are not spin-1 magnons as observed in other un-frustrated 2D quantum magnets but instead are spinons carrying a fractional spin of 1/2, as predicted by a resonating-valence-bond picture. Here we use high magnetic fields to induce a transition from this fractional quantum spin-liquid phase to the fully-polarized phase where spins are ferromagnetically aligned along the field. In this field-induced phase all quantum fluctuations are quenched by the external field and the system is expected to behave like a classical magnet with spin-1 magnon excitations. Measurements are made in fields up to 12 T and temperatures below 0.2 K. Ferromagnetic saturation is observed at the critical field Bc=8.44(1) T∥a. Above Bc the measured excitations lineshapes show well-defined, almost resolution-limited peaks as expected for spin-1 magnons and are gapped throughout the zone. The gap to the lowest energy excitation decreases linearly upon decreasing field and closes at Bc, below which the system orders into a cone phase. This transition provides an opportunity to study how ordered phases arise from the condensation of excitations.
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Received: 18 July 2001 / Accepted: 24 October 2001
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Coldea, R., Tennant, D., Habicht, K. et al. Full ferromagnetic saturation of a two-dimensional quantum antiferromagnet . Appl Phys A 74 (Suppl 1), s904–s906 (2002). https://doi.org/10.1007/s003390101163
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DOI: https://doi.org/10.1007/s003390101163