Successive Majorana topological transitions driven by a magnetic field in the Kitaev model

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 antiferr...

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Bibliographic Details
Published in:Physical review. B 2018-08, Vol.98 (6), p.060416, Article 060416
Main Authors: Nasu, Joji, Kato, Yasuyuki, Kamiya, Yoshitomo, Motome, Yukitoshi
Format: Article
Language:English
Subjects:
Antiferromagnetism
Cones
Ferromagnetism
Hall effect
Honeycomb construction
Magnetic fields
Magnetism
Mean field theory
Phase transitions
Spin liquid
Topology
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Summary: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.
ISSN:2469-9950
2469-9969
DOI:10.1103/PhysRevB.98.060416