Speaker
Description
We investigate the interplay between non-trivial band topology and strong electronic correlations in a two-leg ladder model with a p-wave-like hybridization between the legs. In the non-interacting limit, the model realizes a symmetry-protected topological phase and exhibits three insulating regions, denoted A, B, and C, characterized by free-fermion winding numbers 0, −1, and −2, respectively. Combining density-matrix renormalization group calculations with a continuum field-theoretical analysis of the two critical boundaries, we determine the complete quantum phase diagram in the presence of a repulsive inter-leg density-density interaction. Our analysis, based on the entanglement entropy and entanglement spectrum, reveals a striking dichotomy in the stability
of the topological phases under interactions. In particular, we find that the edge entanglement entropy undergoes a non-trivial change upon introducing interactions. This behavior is explained naturally within the continuum theory, which demonstrates that the two topological phase bound-aries respond qualitatively differently to the same microscopic interaction. The A−C boundary consists of two Dirac valleys located at ±k0 and is described by a free theory with central charge c = 2. The interaction generates an intervalley exchange that gaps the relative axial sector while preserving the total axial symmetry, leaving a single symmetry-protected critical mode with c = 1. Consequently, the interacting critical boundary remains pinned at tc1 = tc2, defining the A′ −C′ transition. In contrast, the B−C boundary contains a single Dirac mode at k = π. Here, the same interaction produces an additive mass renormalization through virtual high-energy modes, shifting the critical point to the B′−C′ boundary while preserving its single-Dirac, c = 1 critical character. These results provide a symmetry-based, interaction-dependent understanding of when a topological phase boundary remains pinned, is shifted, or becomes destabilized.