Sample interview questions: Can you explain the concept of excitonic insulators and their significance in solid-state physics?
Sample answer:
Excitonic Insulators
Excitonic insulators are a unique class of solids where the ground state is characterized by bound electron-hole pairs, known as excitons. Unlike conventional insulators, where the valence and conduction bands are separated by a large energy gap, excitonic insulators exhibit a very small and indirect bandgap.
Formation and Properties:
Excitonic insulators form when the Coulomb attraction between electrons and holes is strong enough to overcome their kinetic energy. This typically occurs in materials with a large effective mass of electrons and holes, such as organic semiconductors and transition metal oxides. The self-trapping of excitons leads to the formation of tightly bound electron-hole pairs with very low mobility.
Properties of Excitonic Insulators:
- Indirect bandgap: The bandgap arises from the energy difference between bound exciton states and the free-carrier states. This indirect bandgap makes excitonic insulators optically inactive.
- Strong excitonic effects: Excitonic insulators exhibit pronounced excitonic effects, such as large exciton binding energies, strong optical absorption, and long exciton lifetimes.
- High electrical resistivity: Due to the immobilization of charge carriers, excitonic insulators exhibit very high electrical resistivity, making them insulating at low t… Read full answer
Source: https://hireabo.com/job/5_0_12/Solid-State%20Physicist