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

TL;DR

This paper explores spin/fermion ladder models with exact multipole phases, revealing non-trivial orderings with zero magnetization and local conserved quantities, and maps out their phase diagrams.

Contribution

It introduces and analyzes multipole phases in spin/fermion ladders with local conserved quantities and higher-order spin generalizations.

Findings

Identification of multipole phases with zero magnetization.

Phase diagrams for ladder geometries with quadratic couplings.

Experimental signatures via dynamical structure factor.

Abstract

We study spin/fermion ladder models with exact multipole phases, which are traditional spin 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 with quadratic spin couplings 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 traditional spin phases of the higher-order spin.