Valley coupling constructed topological two-parameter charge pump

Valley coupling is proposed to construct a spatially separated two-parameter pump based on the O- or Y-shaped Kekul\'e (Kek) graphene superlattices (GSs) with a sandwiched graphene layer. It is shown that for the O-shaped Kek GS pumping structure, pumped charges with an integer number can be obtained in a pumping cycle at the Fermi energy residing in the effective energy gap. Particularly, this quantization only from the contribution of intervalley reflection is thoroughly different from the one in previous two-parameter pumps only with the intravalley reflection. This stems from the Hamiltonian of an antiunitary symmetry, leading to a phase analogous to a topological superconductor and thus a perfect pseudo-Andreev reflection in the valley version. The quantization also can be attributed to the topological interfacial state (TIS) arising in between the two pumping sources due to different quantum valley Hall insulator (QVHI) phases. However, for the Y-shaped Kek GS one, the current coming from both the intravalley and intervalley reflections is nonquantized. This is due to the time-dependent coupling term between two valleys only emerging in the $A$ sublattice, which induces no QVHI and no resultant TISs. Our findings may not only pave a new road to design the quantized charge pump device based on the GS, but also provide a sharp experimental signature to detect the O-shaped one and distinguish between the two GSs.