What Substrates Are Used For Polaritonic Research?

What Is Polariton?

A polariton is a quasiparticle resulting from the strong coupling of a photon with a material excitation, such as an exciton (electron-hole pair), phonon (lattice vibration), or plasmon (collective electron oscillation).

In simple terms:

A polariton is a hybrid light-matter particle—part light, part matter. It inherits properties from both the photon (like high speed and coherence) and the matter excitation (like mass and interactions).

Types of Polaritons:

1. Exciton-Polaritons

   • Formed from the coupling of photons with excitons (bound electron-hole pairs in semiconductors).

   • Often studied in semiconductor microcavities.

   • Can behave like Bose-Einstein condensates at relatively high temperatures.

   • Applications: Polariton lasers, quantum optics.

2. Phonon-Polaritons

   • Arise when photons couple with optical phonons (vibrational modes in crystals).

   • Found in ionic crystals like SiC or GaN.

   • Useful in terahertz and infrared optics.

3. Plasmon-Polaritons

   • Formed by coupling photons with plasmons (oscillations of free electrons at a metal-dielectric interface).

   • Known as surface plasmon-polaritons (SPPs).

   • Used in plasmonics, biosensing, and nanophotonics.

Why Are Polaritons Important?

• They allow light to interact more strongly with matter.

• Enable ultrafast, low-power, and nanoscale devices.

• Key for quantum technologies, nonlinear optics, and next-gen photonic circuits.

• Photons bounce between the mirrors (DBRs).

• Quantum wells in the cavity generate excitons when excited by light.

• The confined photons interact strongly with the excitons, creating exciton-polaritons.

🌀 What Happens in the Cavity:

• The photon energy (E = hf) matches the exciton energy.

• Strong coupling blends the two into a new quasiparticle with:

  • Light-like properties (fast, coherent, can travel)

  • Matter-like properties (can interact, scatter, form condensates)

💡 Application: Polariton Laser

• Traditional lasers require population inversion and high energy.

• A polariton laser works via Bose-Einstein condensation of polaritons—no population inversion needed.

• Advantages:

  • Very low power threshold

  • Operates at room temperature in some materials (e.g., GaN)

  • Compact, efficient, suitable for integrated photonics

🔬 Other Applications:

⚙️ Materials Used:

• Exciton-polaritons: GaAs, GaN, ZnO

• Phonon-polaritons: SiC, h-BN

• Plasmon-polaritons: Gold, Silver, Graphene