Kavli Affiliate: Natalia Chepiga
| First 5 Authors: Aman Sharma, Mithilesh Nayak, Natalia Chepiga, Frédéric Mila,
| Summary:
We study the dynamical structure factor of the frustrated spin-$3/2$
$J_1$-$J_2$ Heisenberg chains, with particular focus on the partially dimerized
phase that emerges between two Kosterlitz-Thouless transitions. Using a valence
bond solid ansatz corroborated by density matrix renormalization group
simulations, we investigate the nature of magnon and spinon excitations through
the single-mode approximation. We show that the magnon develops an
incommensurate dispersion at $J_2 approx 0.32J_1$, while the spinons, viewed
as domain walls between degenerate valence bond solid states, become
incommensurate at $J_2 approx 0.4J_1$ beyond the Lifshitz point ($J_2 approx
0.388J_1$). The dynamical structure factor exhibits rich spectral features
shaped by the interplay between these excitations, with magnons appearing as
resonances embedded in the spinon continuum. The spinon gap shows a
nonmonotonic behavior, reaching a peak near the center of the partially
dimerized phase and closing at the boundaries, suggesting the appearance of a
floating phase as a result of the condensation of incommensurate spinons.
Comparative analysis with the spin-$5/2$ case confirms the universality of
these phenomena across half-integer higher-spin systems. Our results provide
detailed insight into how fractionalization and incommensurate condensation
govern the spectral properties of frustrated spin chains, offering a unified
picture across different spin magnitudes.
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