Abstract:
Strong quantum fluctuations and spin entanglement can lead to exotic emergent many body properties of materials, such as fractionalized excitations predicted for quantum spin liquids, or the field-tuned Bose Einstein Condensation observed in quantum dimer crystals. Traditionally, the materials space in which these types of phases are sought has been limited to materials with “pure" spin 1/2, as obtainable from Cu2+ for instance, and most theories have therefore focused on the isotropic exchange limit. However, attention has recently shifted towards quantum materials in which an interplay of strong spin orbit coupling and crystal field effects lead to a "pseudo-spin" 1/2. The interactions in these materials can be described by anisotropic effective exchange models, which lead to new quantum many body phenomena such as the Majorana fermion excitations of Kitaev quantum spin liquid. To explore quantum phases arising from anisotropic exchange, we are searching for new materials hosting a spin-orbit coupled pseudo-spin 1/2. I will show our first results on one such material, which forms a quantum dimer crystal on a distorted honeycomb lattice. Despite the expected lack of continuous symmetry of the exchange interactions, a robust goldstone mode is clearly observed in the field-induced phase.