Substantial enhancement of nonlinear high-order harmonics generation based onFano-resonant nanostructures has received growing interest due to theirpromising potential for developing integrated and advanced next-generationnanophotonic devices. In this study, going beyond conventional subwavelengthstructures, we propose an optothermally functional hetero-metallodielectricasymmetric eight-member octamer cluster composed of a central silicon nanodiskand peripheral disks with a phase-change material (Ge2Sb2Te5). Using fullelectromagnetic calculations, we show that in the amorphous phase of thesurrounding particles, the oligomer acts as an all-dielectric cluster, while inthe crystalline regime, the octamer turns into a hybrid metallodielectricassembly. Exploiting the exquisite ability of supporting distinct Fanolineshapes at different wavelengths depending on the phase of Ge2Sb2Te5, weshowed the generation of both second and third harmonics at amorphous andcrystalline phases of GST nanodisks, respectively with the produced harmonicwavelengths of 425 nm and 317 nm, respectively. Our calculations for thecorresponding conversion efficiencies revealed significant enhancements as{\eta}SHG=0.012% and {\eta}THG=0.0081% for SHG and THG, respectively. Such anexquisite feature of multiresonant optothermally tunable cluster allowsgeneration of several higher-harmonics with distinct intensities using a singlesystem for future photonics applications.
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