Fractonic Constraints and Magnetic Order in a Dipole-Conserving Spin Chain
This work investigates the competition between dipole conservation, which imposes strong dynamical constraints and prevents the propagation of isolated spin excitations, and Ising-type interactions that favor ordering. Specifically, we explore the ground state phase diagram of a one-dimensional spin chain in the presence of both fractonic constraints and interactions. Despite the kinetic constraints, the system stabilizes an antiferromagnetic dipole-ordered ground state, where the ordering occurs at the level of spin pairs rather than individual spins. At a large Ising interaction strength, the model undergoes a phase transition from a dipole-ordered phase to a spin antiferromagnetic phase. In contrast, for ferromagnetic Ising interactions, the model exhibits both antiferromagnetic and ferromagnetic dipole ordered phases. At sufficiently large negative interaction strength, the dipole ordered phase transitions to a ferromagnetic phase with conventional spin ferromagnetic order. To characterize these distinct phases, we employ density matrix renormalization group (DMRG) simulations alongside large-scale diagonalization. We analyze appropriate order parameters, along with features of the entanglement spectrum and dynamical spectral functions. In limiting cases, the observed transitions can be understood by mapping the dipole conserving model onto effective XXZ models in a restricted Hilbert space of composite spins.