[en] Full text: When we sandwiched a high-temperature superconductor between two layers of specific Manganite last year, we discovered a that the superconductor adopts a startling new ground state. This 'superconductor sandwich' exhibit many unusual effects; an exotic granularsuperconductor that transitions in a strong magnetic field to a ‘customary’ superconductor. Here, we highlight how we used state-of-the-art THz ellipsometry (Fig. 1) in conjunction with synchrotron-based x-ray studies and transport measurements to reveal the ground-state nature of our superconductor sandwiches. We'll also present some ways we think other spectroscopic probes could be used to elucidate the physics behind these unusual effects. Aside from being a fascinating system to study in its own right, the discovery provides a novel way to study the physics of high-temperature superconductors. It is also a great example of the surprising and useful behaviours that can be realised at engineered interfaces. Figure 1: The optical conductivity measured by ellipsometry of the Superconductor- Manganite sandwich, from the THz to near UV. The superconductor layer is 7 nm thick, each of the Manganite layers 20 nm thick. The large peak around 10 cm^-1 and low temperature is evidence of the unusual granular-superconductor. (author)