Casimir-like Excitonic States from Twin-Structured Type-II Core/Shell Quantum Dots

The Casimir effect, where conducting plates restrict electromagnetic vacuum modes, is a cornerstone of quantum field theory but has no known analogue in semiconductor excitonic systems. Here we report a Casimir-like excitonic state in twin-structured type-II core/shell quantum dots, where the two-core geometry analogously suppresses hole wave functions. Using a finite-difference effective-mass framework, we identify three excitonic states in CdS/ZnSe quantum dots: a weakly confined state, a Casimir-like state in which the intercore gap suppresses the hole wave function by analogy with conducting plates in the Casimir effect, and a bonding state with intercore hole delocalization. Energy-distance analysis reveals a characteristic intercore gap where the Casimir-like force vanishes, marking the attractive-repulsive transition. The exciton binding energy remains nearly invariant across all three states, contrasting with single-core QDs where it varies streriously. These results establish intercore geometry as an effective degree of freedom for exciton engineering in multicore quantum dot architectures.