12. December 2017
The field-induced quantum spin-liquid phase of α−RuCl3 is gaplessThroughout 2017, the material α−RuCl3 has continued to inspire and fascinate those interested in correlated condensed matter. New experimental data now provide unique insight, and pose fresh challenges.
The motivation for much of the current work on α−RuCl3 is that the material might be a realization of the Kitaev model, an exactly soluble spin model on the honeycomb lattice that contains topological quantum spin liquid (QSL) states of both gapped and gapless persuasions. The prospect of having a material in which the Kitaev model experimentally are intriguing, but the fingerprints available to date have been rather tenuous, leaving it unclear either how close α−RuCl3 really comes to realizing the Kitaev model or what any more robust fingerprints should look like, especially when a magnetic field is applied.
The team demonstrates that, beyond the quantum phase transition at a field of 7.5 T applied in the honeycomb plane, the high-field QSL has gapless spin excitations over a field range up to 16 T. These modes have cone-type dispersion branches, meaning that their density of states vanishes at the lowest energies, which indicates why they are hard to detect by less sensitive methods. Theoretically, these appear to be Dirac-type excitations rather than being of the Majorana type expected in the pure Kitaev model, and experimentally they become gapped when the field is applied out of the plane. This highly unconventional behaviour is not a feature of either Heisenberg or Kitaev magnets, and thus suggests that the physics of α−RuCl3 is dominated by interactions beyond both models.
ContactDr. Bruce Normand
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 2297, e-mail: firstname.lastname@example.org
Original Publication1. Gapless spin excitations in the field-induced quantum spin liquid phase of α−RuCl3
Zheng J, Ran K, Li T, Wang J, Wang P, Liu B, Liu Z-X, Normand B, Wen J, Yu W
Physical Review Letters, 119: 227208, 2017