NEWS
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Congratulations Vinod & Dipendranath for the publication in Phys. Rev. Applied.
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Congratulations Santu K. Bera, for winning M.P. Young Scientist Award 2023 (1st position)
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Congratulations Pravrati and Riyanka for the publication in Surf Interface Anal.
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Congratulations Ankit for best poster award (Dec, 2022).
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Congratulations Ajay for the Publication in Chemistry of Materials (Dec, 2022)
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Congratulations Santu for the publication in Nano Letters (Nov, 2022).
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Congratulations Megha!!! Sixth Dr. from the group (August, 2022 ).
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Congratulations Ankit for winning for Incubic grant to attend the FIO conference.
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Congratulations Pravrati for wining incubic milton grant for CLEO 2022.
OUR LATEST RESEARCH
Atom-like interaction and giant BGR in atomically thin TMDCs
Coulomb interactions in atomically thin transition metal dichalcogenides can be dynamically engineered by exploiting the dielectric environment to control the optical and electronic properties. Here we demonstrate an optically tunable giant band-gap renormalization (BGR) ∼ 1200 and 850 meV from the edge of the conduction band and complete suppression of the exciton absorption in large-area single-layer (1L) and three-layer (3L) MoS2, respectively. The observed giant BGR is two orders of magnitude larger than that in the conventional semiconductors, and it persists for tens of ps. Strikingly, our results demonstrate photoinduced transparency at the electronic band gap using an intense optical field at room temperature. Exciton bleach recovery in 1L and 3L show a contrasting fluence-dependent response, demonstrating the layer-dependent optical tuning of exciton lifetime in a way that would be both reversible and real time.We find that the optical band gap (exciton resonance peak) shows a transient redshift followed by an anomalous blueshift from the lowest energy point as a function of the photo-generated carrier density. The observed exciton energy shift is analogous to atom-atom interactions, and it varies as a Lennard-Jones like potential as a function of the interexciton separation.
[Santu K. Bera et. al., Phys. Rev. B Lett. 104, L201404 (2021)]
Intervalley polaronic biexcitons in metal halide perovskite quantum dots
The strong band edge exciton-phonon interactions in metal halide perovskite quantum dots (QDs) offer a unique platform to explore many-body phenomena. Employing CsPbBr3 QDs as a perovskite model system, we report the observation of spin-selective polaronic biexcitons using collective excitations of two circularly polarized ultrafast lasers of a duration that is two orders of magnitude shorter than the exciton lifetime and one order of magnitude shorter than the spin relaxation time. The intervalley polaron pairing of charge carriers determines the anomalously strong exciton-exciton interactions, where the Haynes factor is an order of magnitude larger than the bulk and five times larger than the two-dimensional and quantum well semiconductors, demonstrating a very robust correlation of excitons. Our findings reveal a mechanism of generating highly stable biexciton states even at room temperature to realize higher-order correlations of charge carriers such as quantum droplets and Bose-Einstein condensates.
[Ajay K. Poonia et. al., Phys. Rev. B Lett. 104, L161407 (2021)]
Novel heterostructures with enhanced nonlinear optical response
The nonlinear optical absorbance of conventional materials is very weak, yet its magnitude dominates device performance in, for example, optical limiting and pulse shaping. Therefore, achieving a strong nonlinear optical response is a longstanding goal. We propose charge transfer between donor and acceptor materials as a means to greatly enhance nonlinear response, toward the realization of high-performance optical limiters. Excellent agreement between experiment and theory for a test hybrid material validates the idea, and guides the design and fabrication of an actual liquid-cell-based absorptive optical limiter, which outperforms benchmark devices.
[R. Yadav et. al., Phys. Rev. Applied 9, 044043 (2018)]
Exciton many body interactions in colloidal perovskite nanocrystals
Exciton many body interactions is the fundamental light–matter interaction which determines the optical response of the new class of colloidal perovskite nanocrystals of the general formula CsPbX3 [X = Cl or Br or I]. However, the understanding of exciton many body interactions manifested through the transient bi-excitonic Stark effect at the early time scales and the Auger recombination process in this new class of materials still remain rather incomplete. We are focussing on the many body exciton interactions under controlled conditions through ultrafast transient absorption spectroscopy. A large bi-excitonic redshift ∼30 meV to the effect of hot excitations on the excitonic resonance is observed at the early timescales. Fluence dependent studies show two-fold degenerate band edges. This explicit experimental evidence for the exciton many-body interactions in CsPbBr3 nanocrystals provides a powerful tool to explore the development of their prospective applications in light emitting devices, lasers, and solar cells.
[Aneesh J. et. al., J. Phys. Chem. C, 121 4734 (2017) ]