We investigate the nature of the topological quantum phase transition between
the gapless and gapped Kitaev quantum spin liquid phases away from the exactly
solvable point. The transition is driven by anisotropy of the Kitaev couplings.
At the critical point the two Dirac points of the gapless Majorana modes merge,
resulting in the formation of a semi-Dirac point with quadratic and linear band
touching directions. We derive an effective Gross-Neveu-Yukawa type field
theory that describes the topological phase transition in the presence of
additional magnetic interactions. We obtain the infrared scaling form of the
propagator of the dynamical Ising order parameter field and perform a
renormalization-group analysis. The universality of the transition is found to
be different to that of symmetry-breaking phase transitions of semi-Dirac
electrons. However, as in the electronic case, the Majorana fermions acquire an
anomalous dimension, indicative of the breakdown of the fractionalized
quasiparticle description.Comment: 5 pages, 4 figures, 1 tabl