Intermediate gapless phase and topological phase transition of Kitaev model in a uniform magnetic field

TL;DR

This paper investigates the phase transitions and gapless regimes of the Kitaev spin liquid under a uniform magnetic field, revealing a topological transition and a robust intermediate gapless phase driven by symmetry and particle-hole asymmetry.

Contribution

It introduces a mean field theory approach revealing a topological phase transition and a stable intermediate gapless phase in the Kitaev model under magnetic field, supported by dynamical mean field results.

Findings

Discovery of a robust intermediate gapless phase in the Kitaev model.

Identification of a topological phase transition at a critical magnetic field.

Confirmation of phase diagrams through dynamical mean field theory.

Abstract

We study the Kitaev spin liquid (KSL) in a [001] magnetic field employing the mean field theory (MFT/MF) in the Majorana fermion representation. The MF Hamiltonian of the system has the Bogoliubov de-Gennes (BdG) form of a 2D Weyl superconductor. We discover a robust gapless regime in intermediate magnetic field for both gapless and gapped AFM KSL with Jx = Jy before the system is polarized in high magnetic field. A topological phase transition (PT) connecting two gapless phases with nodal lines takes place at a critical magnetic field hc1 in this regime. While the nodal lines at hc1 is protected by the mirror symmetry with Jx = Jy and disappear at Jx 6= Jy with a gap opening near the critical field, the nodal points at E = 0 can exist at intermediate fields even without mirror symmetry. We reveal that the phase evolution of the KSL in the magnetic field is driven by the competition between the magnetic field and the particle-hole (p-h) asymmetry of the normal state of the BdG Hamiltonian, which results in the robust intermediate gapless phase for AFM KSL. For FM KSL, there is no intermediate PT before polarization. The above phase diagrams are confirmed by dynamical MFT (DMFT) results.