Multipole phases in a type of spin/fermion ladders with local conserved quantities and generalizations

Abstract: We study spin/fermion ladder models with multipole phases, which are traditional transverse-field-Ising phases formed by multipole moments. These phases feature non-trivial order with zero magnetization. The multipole models have dimer local conserved quantities that are Ising terms of spin. The Hilbert spaces are locally fragmented into independent sectors described effectively by {\it higher-order spin}. For dipole models, we consider two ladder geometries and work out the phase diagrams. Different phases of the model can be distinguished experimentally with the dynamical structure factor. Higher-order multipole models are obtained by introducing more dimer conserved quantities. The phases are characterized by the values of the local conserved quantities and the transverse-Ising phases of the higher-order spin.