Quantum criticality and confinement in weak Mott insulators

Electrons undergoing a Mott transition may shed their charge but persist as neutral excitations of a quantum spin liquid (QSL). We introduce concrete two-dimensional models exhibiting this exotic behavior as they transition from superconducting or topological phases into fully charge-localized insulators. We study these Mott transitions and the confinement of neutral fermions at a second transition into a symmetry-broken phase. In the process, we also derive coupled-wire parent Hamiltonians for a non-Abelian QSL and a ${\mathbb{Z}}_4$ QSL.

Figure 1

Phase diagram of a superconductor that undergoes a Mott transition upon increasing the on-site repulsion $u$. The parameter $\lambda$ modifies the spin correlations within the superconductor. Depending on its value, the insulating phase may be a valence bond solid or a ${\mathbb{Z}}_2$ spin liquid. The coupled-wire formalism affords us theoretical control along the dashed line, passing through all phases and phase transitions.