凝縮系セミナー Novel quantum states of matter emergent in Kitaev quantum magnets
e-mail: my@issp.u-tokyo.ac.jp
The exactly solvable Kitaev model on a honeycomb lattice provides a novel platform to achieve an elusive quantum spin liquid and Majorana quasiparticles. In the quest for Kitaev honeycomb magnets, the two-dimensional layered ruthenate α-RuCl3and iridates A2IrO3(A=Na, Li) are considered a prime candidate. In this seminar, I will discuss our group’s endeavor to search the predicted exotic states of matter in Kitaev candidate materials.
First, we present the combined thermodynamic, Raman and neutron scattering results ofα-RuCl3. We provide experimental signatures of itinerant Majorana excitationsas a Y-shape dispersive excitation around the Γ-point and a magnetic continuum obeying Fermi statistics. The spin fractionalization is further corroborated by a two-stage release of magnetic entropy by (R/2)ln2. Second, we address an ensuing question whether Kitaev spin liquids are stabilized in the three-dimensional analogue of the honeycomb iridates, β-andγ-Li2IrO3. Using polarization-resolved Raman spectroscopy, we find that the temperature dependence of the Raman spectral weight is dominated by the thermal damping of fermionic excitations, similar to α-RuCl3. Finally, we discuss an on-going project on the newly discovered copper iridate Cu2IrO3, being in closer proximity to the ideal geometry of the Kitaev honeycomb model than its predecessors A2IrO3(A = Na, Li) mainly due to the eclipsed stacking of adjacent layers. Preliminary characterizations reveal random Kitaev magentism, evading a long-range magnetic order, unlike A2IrO3.