Thermodynamic pitch offset near the ferrimagnetic boundary

Determine whether the extrapolated modulation wavevector near $J_2=0.26$ represents a genuine incommensurability or instead reflects the non-asymptotic finite-size regime close to the first-order ferrimagnetic-to-singlet transition.

Background

In most of the investigated singlet phase, finite-size extrapolations are consistent with a rigid commensurate modulation at q=3π/4q=3\pi/4. However, the point at J2=0.26J_2=0.26, immediately above the first-order boundary, lies measurably above this value in a three-size fit and has a substantially larger residual.

The available system sizes do not establish whether this deviation survives in the thermodynamic limit. Resolving the issue requires larger systems or improved finite-size scaling capable of distinguishing a genuine incommensurate wavevector from pre-asymptotic behavior.

References

It lies next to the first-order boundary $J_2{c1}$; whether it is a genuine incommensurability or the onset of the non-asymptotic regime seen at $L=40$ is not decided by the present data.

— A rigid commensurate host and a defect that switches: vacancies in the frustrated alternating spin-(1, 1/2) Heisenberg chain  (2610.22140 - Silva et al., 15 Oct 2026) in Section 4, The pitch of the singlet phase, subsection “What is not resolved”