Staggered Potential and Elliptical Light Driven Topological Phase Transitions in $\alpha$-${\mathcal{T}}_3$ Lattice

We theoretically investigate the influence of hexagonal boron nitride (h-BN) on the electronic properties of an $\alpha$-${\mathcal{T}}_3$ lattice driven by an off-resonant elliptically polarized light field. The staggered potential $M$ breaks the sublattice inversion symmetry, transforming the initial semimetal into a trivial insulator with Chern number $C=0$. We identify a fundamental geometric singularity at $\alpha =1\mathrm{/}\sqrt{2}$, independent of $M$, below which no finite drive can close the lower band gap, creating a stable topological window where conduction–flat band inversion yields a Chern insulator with $C=1$. Above this critical value the lower gap closes with finite intensity, allowing a transition from $C=1$ to $C=2$ as the dice limit ($\alpha =1$) is approached. The topological phases are characterized by quantized anomalous Hall plateaus at ${\sigma }_{xy}=e^2\mathrm{/}h$ ($C=1$) and ${\sigma }_{xy}=2e^2\mathrm{/}h$ ($C=2$), with each valley contributing exactly $\frac{1}{2}{e}^2\mathrm{/}h$. The $C=1$ plateau remains robust from $0$ K to $300$ K, while $C=2$ requires $T<100$ K due to its narrower gap. A highly asymmetric thermoelectric Seebeck response further serves as an experimental fingerprint of each phase, providing a realistic framework for realizing stable high-Chern-number phases in substrate-supported $\alpha$-${\mathcal{T}}_3$ materials.