Strain-enhanced magnetism in zigzag-edged rhombic graphene quantum dots via quantum Monte Carlo

We investigate interaction-driven magnetism in zigzag-edged rhombic graphene quantum dots using determinant quantum Monte Carlo simulations of the half-filled Hubbard model. Uniaxial strain is incorporated at the tight-binding level through a bond-selective reduction of nearestneighbor hoppings. Although the rhombic geometry is sublattice balanced and therefore has a total-spin singlet ground state at half filling by Lieb’s theorem, we find a pronounced emergence of edge-localized magnetic fluctuations. The susceptibility restricted to the outermost zigzag sites, χ z , strongly exceeds the bulk-averaged response, χ b , and exhibits a marked low-temperature upturn consistent with local moments associated with near-zero-energy zigzag edge states. Increasing the interaction strength enhances both χ z and χ b , with the dominant amplification occurring in the edge sector and the onset of local-moment behavior shifting to higher temperatures. Strain provides an especially efficient tuning knob: reducing selected hoppings selectively boosts the low-temperature edge susceptibility, yielding more than a twofold enhancement for the largest strain considered, while the high-temperature response remains nearly unchanged. Finite-size comparisons indicate weak size dependence over most temperatures, with deviations confined to the lowest-energy regime. These results are consistent with a singlet ground state at half filling accompanied by pronounced edgelocalized magnetic fluctuations, and they identify mechanical strain as a practical route to enhance and control the low-energy edge magnetic response in sublattice-balanced graphene nanostructures.