Discontinuity at the left boundary of the correlation-assisted C = -2 topological phase

Determine whether a discontinuity of the magnetization or superconducting gap occurs at the left-hand boundary of the C = -2 topological superconducting region, near electronic density n ≈ 0.76, where the Chern number changes despite the absence of a resolved bulk single-particle gap closure.

Background

The paper identifies a C = -2 topological superconducting region in the hole-doped part of the phase diagram of the Rashba-coupled t-J-U model under an applied Zeeman field. Its boundaries are associated with changes in the Chern number, but the transition mechanisms differ from the conventional C = -4 transition because the single-particle gap does not close at the C = -2 boundaries.

At the right-hand boundary of the C = -2 region, the authors observe a magnetization jump and attribute it to a correlation-driven first-order transition with phase coexistence. At the left-hand boundary, near n ≈ 0.76, the Chern number changes reproducibly, but the simulations do not resolve a corresponding discontinuity in either the magnetization or the superconducting gap. Clarifying whether a weak first-order transition or another mechanism is responsible remains unresolved.

References

Remarkably, despite a reproducible change of Chern number on the left-hand side of the $C = -2$ TSC state ($n \approx 0.76$), we have not been able to resolve the corresponding discontinuity of either magnetization or SC gap in our simulations.

— Correlation-assisted topological and metamagnetic transitions in Rashba-coupled superconductors: $t$-$J$-$U$ model study  (2609.37812 - Dey et al., 29 Sep 2026) in Section “Correlation-assisted topological transitions”