Strain-driven spin-flop transition and collapse of the giant magnon gap in the bilayer iridate Sr3Ir2O7
Abstract
The bilayer iridate Sr3Ir2O7 is a c-axis collinear antiferromagnet, held there by a giant interlayer pseudodipolar anisotropy, whereas single-layer Sr2IrO4 cants in the ab plane. We show from first principles that biaxial compression of a few percent (εc≈−2.4%) flops the easy axis of Sr3Ir2O7 into the plane. A magnetic model Hamiltonian built from Wannier functions with no fitted parameter---reproducing the giant magnon gap of the bulk, so far known only from fits to experiment---identifies the mechanism. Compression collapses the interlayer exchange channel, whose straight Ir--O--Ir path weakens as the bent in-plane path strengthens. Hund's exchange sets the scale of the anisotropy and, beyond J/U≈0.15, removes the collinear state altogether. The flop is not a rigid rotation---the ordered moments of the two states cross at εc---and it carries a stark fingerprint, in that the giant easy-axis magnon gap collapses to a gapless, Goldstone-like spectrum. Compressively strained films thus sit on a metamagnetic phase boundary ending in a zero-temperature bicritical point, a charge-neutral handle on spin--orbit-entangled order.
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BibTeX
@misc{kim2026straindriven,
title = {{Strain-driven spin-flop transition and collapse of the giant magnon gap in the bilayer iridate Sr$_3$Ir$_2$O$_7$}},
author = {Choong H. Kim},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.22473},
eprint = {2608.22473},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.22473},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Strain-driven spin-flop transition and collapse of the giant magnon gap in the bilayer iridate Sr_3Ir_2O_7
AU - Choong H. Kim
PY - 2026
DA - 2026/08/28
PB - arXiv
DO - 10.48550/arxiv.2608.22473
UR - https://arxiv.org/abs/2608.22473
AB - The bilayer iridate Sr_3Ir_2O_7 is a c-axis collinear antiferromagnet, held there by a giant interlayer pseudodipolar anisotropy, whereas single-layer Sr_2IrO_4 cants in the ab plane. We show from first principles that biaxial compression of a few percent (ε_c≈−2.4%) flops the easy axis of Sr_3Ir_2O_7 into the plane. A magnetic model Hamiltonian built from Wannier functions with no fitted parameter---reproducing the giant magnon gap of the bulk, so far known only from fits to experiment---identifies the mechanism. Compression collapses the interlayer exchange channel, whose straight Ir--O--Ir path weakens as the bent in-plane path strengthens. Hund's exchange sets the scale of the anisotropy and, beyond J/U≈0.15, removes the collinear state altogether. The flop is not a rigid rotation---the ordered moments of the two states cross at ε_c---and it carries a stark fingerprint, in that the giant easy-axis magnon gap collapses to a gapless, Goldstone-like spectrum. Compressively strained films thus sit on a metamagnetic phase boundary ending in a zero-temperature bicritical point, a charge-neutral handle on spin--orbit-entangled order.
ER -