The quantum spin liquid (QSL) is one of the long-sought states of matter in condensed matter physics. To date, geometrically frustrated systems, where antiferromagnetic spins cannot satisfy all magnetic coupling simultaneously, have been the prime playground for QSLs but have been constrained by the lack of exactly solvable model Hamiltonians [1]. Kitaev theoretically contrived another route where a spin-1/2 on a honeycomb lattice interacts through bond-dependent Ising ferromagnetic couplings [2]. The three nearest-neighbor bonds of the honeycomb lattice have their easy-axis orthogonal to the other two, which gives rise to a competition between the three and therefore a strong frustration. The ground state was exactly shown to be a quantum spin liquid by employing the four kinds of Majorana fermions representing the fractionalization of real spins. The presence of Majorana fermions is relevant to quantum computation [3].
The Kitaev model has been a toy model for theoretical studies, but there is now a pathway to materialize the Kitaev model due to chemical-bond-dependent coupling of the Jeff = 1/2 moments in Ir4+ oxides [4]. Very recently, we discovered a QSL state in H3LiIr2O6, synthesized by replacing the interlayer Li in a-Li2IrO3 using a soft chemistry [5]. The presence of a gap in the low energy excitations was suggested. The microscopic origin of QSL, however, remains yet elusive. A quantized thermal Hall effect kxy, believed to be due to a chiral edge state, was observed in a related spin liquid candidate a-RuCl3 under a critical magnetic field to suppress the long-range ordering [6]. The purpose of this project is to improve the understanding of the spin liquid ground state. This will include materials synthesis, measuring thermal (Hall) signatures of exotic quasiparticles and performing measurements of NMR and other spectroscopy studies.
References
[1] L. Savary and L. Balents, Rep. Prog. Phys. 80, 016502 (2016).; Y. Zhou et al., Rev. Mod. Phys. 89, 025003 (2017).
[2] A. Kitaev, Annals of Physics 321, 2 (2006).
[3] Review in A. Stern and N. H. Lindner, Science 339, 1179 (2013).
[4] G. Jackeli and G. Khaliullin, Phys. Rev. Lett. 102, 017205 (2009).
[5] K. Kitagawa et al., Nature 554, 341 (2018).
[6] Y. Kasahara et al., Nature 559, 227 (2018).
Principal investigators / Participating scientists:
H. Takagi
K. Kitagawa