Why strong spin-orbit coupling does not destabilize the Dirac spin liquid in the Yb delafossites
Abstract
The Yb delafossites NaYbSe2, KYbSe2, CsYbSe2 and NaYbO2 are candidates for the U(1) Dirac spin liquid (DSL) of the triangular lattice. Strong spin-orbit coupling gives their exchange an XXZ anisotropy Δ and bond-dependent couplings J±±, Jz± that lock the spin frame to the lattice. We show that, within a single layer of a stable Heisenberg DSL, these couplings generate no relevant Lorentz-scalar operator of their own. Inversion at the bond centers removes the Dzyaloshinskii-Moriya channel that gaps the kagome DSL, so the locked symmetry forbids a mass, density or current at any order and, assuming continuity, any new monopole term through charge three. Every Lorentz-scalar four-fermion operator induced by spin-orbit coupling shares an SU(4) multiplet, and hence its scaling dimension, with a Heisenberg-allowed one, and the nine non-scalar quartics without such a partner arise only at second order and are irrelevant at large N. The Heisenberg DSL itself allows a Lorentz-vector quartic of large-N dimension 2.92, which a stable phase must also render irrelevant. Beyond a single layer, spin-orbit coupling opens an interlayer monopole channel in rhombohedral stacking. If the Heisenberg DSL is instead multicritical, an anisotropy as small as that of KYbSe2 matters only below tens of mK. At the transition to 120∘ order the anisotropy is relevant, and exact diagonalization indicates that easy-plane anisotropy selects the chiral-Ising class. Existing KYbSe2 neutron data below J do not yet fix the K-point exponent, and gapless out-of-plane spin fluctuations at the K point would test the chiral-Ising selection.
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BibTeX
@misc{iqbal2026strong,
title = {{Why strong spin-orbit coupling does not destabilize the Dirac spin liquid in the Yb delafossites}},
author = {Yasir Iqbal},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.04607},
eprint = {2611.04607},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.04607},
}
RIS
TY - UNPB
TI - Why strong spin-orbit coupling does not destabilize the Dirac spin liquid in the Yb delafossites
AU - Yasir Iqbal
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2611.04607
UR - https://arxiv.org/abs/2611.04607
AB - The Yb delafossites NaYbSe_2, KYbSe_2, CsYbSe_2 and NaYbO_2 are candidates for the U(1) Dirac spin liquid (DSL) of the triangular lattice. Strong spin-orbit coupling gives their exchange an XXZ anisotropy Δ and bond-dependent couplings J_±±, J_z± that lock the spin frame to the lattice. We show that, within a single layer of a stable Heisenberg DSL, these couplings generate no relevant Lorentz-scalar operator of their own. Inversion at the bond centers removes the Dzyaloshinskii-Moriya channel that gaps the kagome DSL, so the locked symmetry forbids a mass, density or current at any order and, assuming continuity, any new monopole term through charge three. Every Lorentz-scalar four-fermion operator induced by spin-orbit coupling shares an SU(4) multiplet, and hence its scaling dimension, with a Heisenberg-allowed one, and the nine non-scalar quartics without such a partner arise only at second order and are irrelevant at large N. The Heisenberg DSL itself allows a Lorentz-vector quartic of large-N dimension 2.92, which a stable phase must also render irrelevant. Beyond a single layer, spin-orbit coupling opens an interlayer monopole channel in rhombohedral stacking. If the Heisenberg DSL is instead multicritical, an anisotropy as small as that of KYbSe_2 matters only below tens of mK. At the transition to 120^∘ order the anisotropy is relevant, and exact diagonalization indicates that easy-plane anisotropy selects the chiral-Ising class. Existing KYbSe_2 neutron data below J do not yet fix the K-point exponent, and gapless out-of-plane spin fluctuations at the K point would test the chiral-Ising selection.
ER -