Terahertz cavity Josephson electrodynamics with subwavelength hybrid silicon-high temperature superconductor van der Waals heterostructure arrays

We propose the engineering of ultrastrong light-matter interactions in a deeply subwavelength microcavity array based on hybrid silicon and high-temperature superconducting (HTS) Bi2Sr2CaCu2O8+δ (BSCCO) van der Waals (vdWs) heterostructure. We perform numerical modelling and analytical calculation to describe Josephson terahertz (THz) cavity electrodynamics and ultrastrong coupling between Josephson plasmon polaritons and subwavelength microcavity arrays. The resonance frequency of microcavities is swept through the Josephson plasma frequency by altering their width. THz reflection demonstrates the anti-crossing behaviour of ultrastrong coupling with a normalized Rabi frequency (coupling strength) 2Ω_R/f_c = 0.29 for the BSCCO thickness t= 200 nm, which increases to the value of 0.87 for t= 800 nm.