Strong Dimerization and Field-Induced Reconstruction of the Low-Energy Spectrum in Cu3(OH)4(HCO2)2
Abstract
We investigate the field-dependent low-energy thermodynamics of the distorted triangular quantum antiferromagnet Cu3(OH)4(HCO2)2 using a sector-resolved Superblock Diagonalization Method (SBDM) supplemented by a transfer-matrix treatment of weakly coupled layers. The strong exchange hierarchy, dominated by the Cu1--Cu1 intradimer coupling J2=150 K, separates a high-energy dimer sector from a much softer magnetic manifold formed predominantly by the Cu2 moments. In the 24-site cluster, sixteen Cu1 spins form the strongly bound sector while eight Cu2 spins remain magnetically active; polarization of these eight spins gives Sz=4 compared with Szsat=12, providing a direct microscopic origin for the one-third magnetization scale. The finite-temperature thermodynamics reveals a non-monotonic field evolution of the low-energy scale: the dominant C/T feature softens with increasing field, reaches a minimum near the field region around 2 T, and subsequently hardens as the low-temperature magnetization approaches Msat/3. Temperature and field sweeps thus expose a common field-induced spectral reconstruction, while the strongly reduced entropy reflects the restricted number of thermally active degrees of freedom below the dimer excitation scale. Our results identify strong-dimer-induced reduction of the active magnetic Hilbert space, followed by field-driven reorganization of the residual spin sector, as the common microscopic origin of the one-third magnetic response and the non-monotonic low-temperature thermodynamics.
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BibTeX
@misc{rahaman2026strong,
title = {{Strong Dimerization and Field-Induced Reconstruction of the Low-Energy Spectrum in $\mathrmCu_3(\mathrmOH)_4(\mathrmHCO_2)_2$}},
author = {Sk Saniur Rahaman and S. R. Hassan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2609.39966},
eprint = {2609.39966},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.39966},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Strong Dimerization and Field-Induced Reconstruction of the Low-Energy Spectrum in Cu_3(OH)_4(HCO_2)_2
AU - Sk Saniur Rahaman
AU - S. R. Hassan
PY - 2026
DA - 2026/10/01
PB - arXiv
DO - 10.48550/arxiv.2609.39966
UR - https://arxiv.org/abs/2609.39966
AB - We investigate the field-dependent low-energy thermodynamics of the distorted triangular quantum antiferromagnet Cu_3(OH)_4(HCO_2)_2 using a sector-resolved Superblock Diagonalization Method (SBDM) supplemented by a transfer-matrix treatment of weakly coupled layers. The strong exchange hierarchy, dominated by the Cu1--Cu1 intradimer coupling J_2=150 K, separates a high-energy dimer sector from a much softer magnetic manifold formed predominantly by the Cu2 moments. In the 24-site cluster, sixteen Cu1 spins form the strongly bound sector while eight Cu2 spins remain magnetically active; polarization of these eight spins gives S^z=4 compared with S^z_sat=12, providing a direct microscopic origin for the one-third magnetization scale. The finite-temperature thermodynamics reveals a non-monotonic field evolution of the low-energy scale: the dominant C/T feature softens with increasing field, reaches a minimum near the field region around 2 T, and subsequently hardens as the low-temperature magnetization approaches M_sat/3. Temperature and field sweeps thus expose a common field-induced spectral reconstruction, while the strongly reduced entropy reflects the restricted number of thermally active degrees of freedom below the dimer excitation scale. Our results identify strong-dimer-induced reduction of the active magnetic Hilbert space, followed by field-driven reorganization of the residual spin sector, as the common microscopic origin of the one-third magnetic response and the non-monotonic low-temperature thermodynamics.
ER -