  The proximity coupled topological insulator / superconductor (TI/SC) bilayer
system is a representative system to realize topological superconductivity. In
order to better understand this unique state and design devices from the TI/SC
bilayer, a comprehensive understanding of the microscopic properties of the
bilayer is required. In this work, a microwave Meissner screening study, which
exploits a high-precision microwave resonator technique, is conducted on the
SmB6/YB6 thin film bilayers as an example TI/SC system. The study reveals
spatially dependent electrodynamic screening response of the TI/SC system that
is not accessible to other techniques, from which the corresponding microscopic
properties of a TI/SC bilayer can be obtained. The TI thickness dependence of
the effective penetration depth suggests the existence of a bulk insulating
region in the TI layer. The spatially dependent electrodynamic screening model
analysis provides an estimate for the characteristic lengths of the TI/SC
bilayer: normal penetration depth, normal coherence length, and the thickness
of the surface states. We also discuss implications of these characteristic
lengths on the design of a vortex Majorana device such as the radius of the
vortex core, the energy splitting due to intervortex tunneling, and the minimum
thickness required for a device.
