Figure 2.

The topological winding numbers $w_0$ [in panel (a)] and $w_{\pi }$ [in panel (b)] versus the real and imaginary parts of the vertical hopping amplitude $J_y^r$ and $J_y^i$. The other system parameters are chosen as $(J_x,J_d,V)=(0.5\pi ,4\pi ,0.1\pi )$. In both panels, each region with a uniform color corresponds to a Floquet topological phase of the non-Hermitian periodically quenched two-leg ladder (PQTLL) model, with the values of winding numbers $(w_0,w_{\pi })$ denoted explicitly therein. The lines separating different regions are the boundaries between different topological phases, which can be obtained numerically from the gap closing conditions ${\Delta }_0=0$ and ${\Delta }_{\pi }=0$ with the help of Equations (9) and (10).