• non-local
• heterostructures
• graphene
• coupling
• 2D materials
• polaritons

Light matter-interaction and our understanding of it led to the development of many key photonic technologies such as lasers, LEDs, photodetectors and solar cells. The basic concept exploited in all these technologies is the quantized nature of electronic transitions in matter. For the mid-IR and THz wavelength region it is of particular interest to control transitions between the quantized levels of charge carriers confined in nano-scale quantum wells (QW) - so called intersubband (ISB) transitions. Another main aspect of light-matter interaction is light connement in highly subwavelength volumes. This confinement of radiation leads to a huge increase in field intensity, thus allowing new interaction regimes such as ultra-strong coupling and cavity QED. An example is given by surface polaritons, which are quasiparticles resulting from the coupling of electromagnetic waves with an electric (or magnetic) dipole, like surface plasmons (SPs) at a metal-dielectric interface. The goal of this work is to combine these two concepts and study the interaction between QWs and light confined to subwavelength scales. This is of great interest for both fundamental science and technological implications. In fact, if this coupling was better understood and observed, new phenomena could be explored such as electrical tunability of the emission frequency. This would allow the fabrication of new versatile devices working in the mid-IR and THz regions, like for instance high-efficiency photodetectors. One could also exploit this coupling to solve the problem of easily launching polaritons, as electrical excitation would
become possible. Two dimensional (2D) materials are an excellent platform to explore this coupled regime. They span the entire range of electronic properties, from insulators to metals. In particular, there are semiconductors forming natural QWs in which ISBs have been observed and many materials in which it is possible to excite dierent kinds of surface polaritons, like hyperbolic phonon polaritons in hexagonal boron nitride and plasmon polaritons in graphene. Moreover, 2D materials can be combined into so-called van der Waals heterostructures, where each 2D material is used as a building block with different properties, allowing to achieve unprecedented effects. In this work we present the design, fabrication and characterization of van der Waals heterostructures for coupling ISB transitions in 2D quantum wells with two different 2D surface polaritons: plasmon polaritons in graphene and hyperbolic phonon polaritons in hexagonal boron nitride.