Emergent dimensional reduction in a distorted kagome magnet $\mathrm{YCa_3(CrO)_3(BO_3)_4}$ driven by exchange hierarchy

Abstract

Frustrated kagome magnets provide a fertile platform for unconventional collective quantum phenomena, yet the role of lattice distortion in reorganizing magnetic degrees of freedom and controlling low-energy physics remains poorly understood. Here we report a rare realization of dimensional reduction in the distorted kagome material $\mathrm{YCa_3(CrO)_3(BO_3)_4}$, combining thermodynamic experiments with first-principles calculations and large-scale Monte Carlo simulations. Magnetic susceptibility and specific heat show no signatures of spin freezing or long-range magnetic order down to $65~\mathrm{mK}$ despite strong antiferromagnetic interactions. Instead, the susceptibility exhibits a broad maximum characteristic of quasi-one-dimensional spin correlations, while the magnetic specific heat follows a robust power law $C_{\mathrm{mag}}\sim T^2$ over more than a decade in temperature that remains unchanged in applied magnetic fields. This field-independent scaling rules out impurity or conventional magnon contributions and points to a collective low-energy excitation spectrum governed by frustration and local constraints. We show that a strongly hierarchical exchange network reorganizes the system into local antiferromagnetic dimers and weakly coupled spin chains, with frustrated inter-unit couplings suppressing three-dimensional order to ultralow temperatures. Our results demonstrate how a hierarchy of competing exchange interactions can reorganize a frustrated three-dimensional magnet into effectively lower-dimensional correlated units, stabilizing extended regimes of quantum-disordered behavior in realistic materials.