Hyperbolic plasmon–phonon dispersion and tunable spontaneous emission enhancement in Ge2Sb2Te5-based multilayer graphene and hBN system

Abstract

Active tunability of phonon dispersion and spontaneous emission (SE) still remain open owing to its exciting application potential. In this study, multilayer graphene and hexagonal boron nitride (hBN) combined with the Ge2Sb2Te5 (GST) functional substrate are proposed to obtain tunable hyperbolic plasmon–phonon dispersion and SE. Results indicate that GST phase change has a profound impact on hyperbolic phonon polaritons in the hBN layer and can obtain an actively tunable SE. Moreover, when graphene is introduced into the hBN/GST system, hyperbolic plasmon–phonon polaritons inside the two reststrahlen (RS) bands of hBN and surface plasmon–phonon polaritons outside the two RS bands can be achieved, both of which can be actively tuned by adjusting the GST phase state and graphene chemical potential. In addition, the coupled polariton branches between hBN phonon polaritons and graphene plasmons become stronger and corresponding SE enhancement regions obviously broaden with increasing the graphene/hBN layer numbers for the fixed thickness multilayer graphene/hBN on GST substrate. These characteristics may provide an available route to realize active tunability of both phonon dispersion and SE enhancement of natural or artificial hyperbolic materials.