Research Projects

The interactions of light with quantum particles, namely excitons, free carriers, spin, and phonons, offer a unique platform to explore the many-body phenomena at the nanoscale. The real-time manipulation of their non-equilibrium dynamics and many-body physics could play an important role in controlling the electronic and optical properties and lead to several emerging quantum technologies like sensing and quantum information processing. The condensation of charge carriers confined at a semiconductor nanocrystal known as electron-hole liquid (EHL) is an ideal platform to explore the exotic state of matter where the macroscopic wave function of correlated particles behaves as a unique collective quantum state of matter. The EHL phase is difficult to observe under ambient conditions due to the excess thermal energy and the low binding energy of the correlated particles. However, EHL is realized at extreme conditions, like cryogenic temperature and in materials having multivalley indirect band-structure, restricting their potential applications in high-performance devices in photonics. Here, we plan to explore experimentally and theoretically EHL and plasma state in the direct bandgap metal halide perovskite nanocrystals (MHPN) using circularly polarized ultrafast pump-probe pulses of near bandgap from cryogenic to room temperatures, engineering the threshold gain for lasing through shape and temperature. Another fascinating phenomenon of semiconductor nanocrystals is multiple-exciton generation (MEG) in which two or more carriers are generated by absorbing a single high-energy photon. The current state-of-the-art materials showing MEG suffer a high loss due to fast carrier thermalization. Since the MEG process competes with hot-carrier thermalization, the intrinsic phonon bottleneck leading to slow hot-carrier thermalization observed in perovskite nanocrystals makes this material highly promising for MEG. However, the previously studied MEG in Pb-based perovskites (CsPbBr3, CsPbI3, and FAPbI3) have a band gap in the visible wavelength, making them impractical for solar cell applications. Interestingly, in a new class of mixed-metal halide perovskites such as partial substitution Pb with Sn/Yb/Er, FACsSnI3, FAMACsPbSnI3, etc., the bandgap can be reduced to NIR region. The important outcomes are the observation of EHL at room temperature provides a completely new landscape for future physical investigations and applications in lasing, optical detection, and modulation. Our proposed idea of reducing MEG by doping with Sn/Yb/Er as low as the ultimate energy conservation limit of 2Eg can be useful for a plethora of applications. Here, we propose that gain threshold for amplified spontaneous emission can be lowered by many folds by modulating the Auger recombination rates and thermalization time to the emitting states. These studies provide a new design strategy for nanocrystal lasers.