Vacancy-induced Low-energy States in the Kitaev Model

Since 2006, the Kitaev honeycomb model has attracted significant attention due to the exactly solvable spin-liquid ground state with fractionalized Majorana excitations [1] and the possible materialization in magnetic Mott insulators with strong spin-orbit couplings [2]. Recently, the 5d-electron compound H₃LiIr₂O₆ has shown to be a strong candidate of Kitaev physics considering the absence of long-range ordered magnetic state [3]. In this work, we demonstrate that a finite density of random vacancies gives rise to a remarkable pile up of low-energy states and possibly explains the experimental findings in H₃LiIr₂O₆. We study both the free-flux and the vacancy-induced bound-flux background and their responses to additional time-reversal symmetry-breaking term, which imitates the magnetic field in real experiments.

[1] A. Kitaev, Ann. Phys. 321, 2 (2006).
[2] G. Jackeli and G. Khaliullin, Phys. Rev. Lett. 102, 017205 (2009).
[3] K. Kitagawa, T. Takayama, Y. Matsumoto, A. Kato, R. Takano,Y. Kishimoto, S. Bette, R. Dinnebier, G. Jackeli, and H. Takagi, Nature 554, 341 (2018).