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arXiv · 1805.02423

Successive Majorana Topological Transitions Driven by a Magnetic Field in the Kitaev Model

Joji Nasu·Yasuyuki Kato·Yoshitomo Kamiya·Yukitoshi Motome
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Abstract

We study quantum phase transitions in the honeycomb Kitaev model under a magnetic field, focusing on the topological nature of Majorana fermion excitations. We find a gapless phase between the low-field gapless quantum spin liquid and the high-field gapped forced-ferromagnetic state for the antiferromagnetic Kitaev model in the [001] field by using the Majorana mean-field theory, in conjunction with the exact diagonalization and the spin-wave theory supporting the validity of this approach. The transition between the two gapless phases is driven by a topological change of the Majorana spectrum --- line node formation interconnecting two Majorana cones. The peculiar change of the Majorana band topology is rationalized by a sign change of the effective Kitaev coupling by the magnetic field, which does not occur in the ferromagnetic Kitaev case. Upon tilting the magnetic field away from [001], the two gapless phases become gapped and topologically nontrivial, characterized by nonzero Chern numbers with different signs. The sign change of the Chern number leads to a reversal of the thermal edge current in the half-quantized thermal Hall effect.

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Joji Nasu, Yasuyuki Kato, Yoshitomo Kamiya, Yukitoshi Motome. 2018-05-07. Successive Majorana Topological Transitions Driven by a Magnetic Field in the Kitaev Model. https://doi.org/10.1103/physrevb.98.060416

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