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arXiv · 2302.09088

Magnetic fragmentation and fractionalized Goldstone modes in a bilayer quantum spin liquid

Aayush Vijayvargia·Emilian Marius Nica·Roderich Moessner·Yuan-Ming Lu·Onur Erten
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Abstract

We study the phase diagram of a bilayer quantum spin liquid model with Kitaev-type interactions on a square lattice. We show that the low energy limit is described by a $\pi$-flux Hubbard model with an enhanced SO(4) symmetry. The antiferromagnetic Mott transition of the Hubbard model signals a magnetic fragmentation transition for the spin and orbital degrees of freedom of the bilayer. The fragmented "N\'eel order" features a non-local string order parameter for an in-plane N\'eel component, in addition to an anisotropic local order parameter. The associated quantum order is characterized by an emergent $\mathbb{Z}_{2} \times \mathbb{Z}_{2}$ gauge field when the N\'eel vector is along the $\hat{z}$ direction, and a $\mathbb{Z}_2$ gauge field otherwise. We underpin these results with a perturbative calculation, which is consistent with the field theory analysis. We conclude with a discussion on the low energy collective excitations of these phases and show that the Goldstone boson of the $\mathbb{Z}_{2} \times \mathbb{Z}_{2}$ phase is fractionalized and non-local.

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Aayush Vijayvargia, Emilian Marius Nica, Roderich Moessner, Yuan-Ming Lu, Onur Erten. 2023-02-17. Magnetic fragmentation and fractionalized Goldstone modes in a bilayer quantum spin liquid. https://doi.org/10.1103/physrevresearch.5.l022062

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