Terminable Transitions in a Topological Fermion Ladder

Interacting fermion ladders are believed to exhibit various Mott-insulator regions as quantum

phases, such as the D-Mott and S-Mott phase. They hold pre-formed electron pairs and become

paired liquids (d-wave and s-wave) upon doping. We show that D-Mott and S-Mott are in fact

two facets of the same topological phase and that the transition between them is terminable. This

bears similarity to the well-known terminable liquid-gas transition, but is richer in the sense that

the transition can be either second order or first order, depending on the interaction details. The

findings are based on numerically obtained ground-state properties and spectral functions using

the variational uniform matrix-product state (VUMPS) formalism. We also provide analytical and

field-theoretical explanations.