arXiv subjects

Sudipta Seth

Publications and source records attributed to Sudipta Seth.

4 recordsLinked to original sources

arXiv2026

Room Temperature Collective Blinking and Photon Bunching from CsPbBr3 Quantum Dot Superlattice

Development of quantum light sources and search for quantum systems capable of supporting collective many-body states are crucial for further progress of modern quantum technologies. Metal halide perovskite quantum dots (QDs) have emerged as a promising candidate for quantum light sources, as individual QDs are reliable single photon emitters even at room temperature. However, photon bunching, a key signature of collective many-body states, has been so far largely observed at cryogenic temperatures in perovskite materials, limiting their applications under ambient conditions. Here, we report the observation of collective blinking and photon bunching in perovskite QD superlattices at room temperature. Sub-wavelength-sized (100 - 500 nm) CsPbBr3 QD superlattices, fabricated via a self-assembly process, exhibit an unusual two-level blinking behavior similar to that of single QDs, and demonstrate photon bunching with a degree of up to 2.75. Time-resolved photoluminescence (PL) measurements and super-resolution imaging reveal that the superlattices have a significantly longer PL lifetime than individual QDs and that their emission is spatially confined to regions tens of nanometers in size. These observations suggest long-range exciton migration to a localized energy trap within the superlattice. Excitation power dependent degree of bunching and analysis of the bunching dynamics indicate that the photon bunching originates from exciton-biexciton cascade emission, a key mechanism for generating entangled photons. These findings establish perovskite QD superlattices as a promising platform for room-temperature collective optical phenomena and quantum light generation, advancing scalable quantum photonic technologies.

physics.optics↗

arXiv2025

M3Scope a 3D multimode multiplane microscope for imaging nanoscale dynamics in soft matter

Fast, volumetric imaging that integrates multiple imaging modalities is essential for probing dynamic, heterogeneous soft and biological matter. Here, we present the M3Scope, a simple yet versatile multiplane microscope that extends widefield detection with a modular multimode cube to enable dual color fluorescence, polarization-resolved, and correlative brightfield fluorescence imaging while (i) preserving simultaneous 3D acquisition at high frame rates (100 fps) and (ii) requiring minimal realignment. We demonstrate its potential by investigating polymer dynamics across multiple spatial and temporal scales. In an acrylamide type polymerizing network, dual color tracking of 100 nm and 300 nm fluorescent probes revealed size dependent viscosities diverging from 15 mPa.s to 40 mPa.s after gelation. Polarization resolved rotational tracking of gold bipyramids yielded viscosities within 10 percent of theoretical values in 80 to 95 percent glycerol and remained accurate in the high-viscosity regime (bigger than 400 mPa.s) where translational motion is undetectable. Fluorescence brightfield imaging correlated structural changes during poly(isopropyl acrylamide) (pNIPAM) phase separation as well as variations in tracer diffusivity, linking morphology and dynamics in 3D. Taken together, these results show that the M3Scope delivers high speed volumetric imaging with flexible modality switching, providing a powerful platform for studying dynamic, heterogeneous systems across disciplines, from polymer physics to cell mechanobiology.

physics.optics↗

arXiv2025

Three-dimensional Optical Reconstruction of colloidal electrokinetics via multiplane imaging

Sorting, filtering, moving and controlling colloidal particles is crucial in many fields, ranging from chemistry to biology and physics. Dielectrophoresis is an outstanding tool for the manipulation of small particles by AC electric fields, due to its high selectivity and the absence of the need for labels. We use a new theoretical-experimental approach to study the dynamics of fluorescently labeled polystyrene nanoparticles of 200 nm under positive and negative dielectrophoresis conditions. Our multiplane widefield microscopy technique combined with single particle tracking offers real-time ($>$ 100 fps) superresolved visualization of colloidal dynamics in three spatial dimensions. This real-time 3D imaging technique allows the reconstruction of superresolved trajectories, enabling the visualisation of local forces with unprecedented detail. To interpret this data, a dedicated multiscale modeling approach was developed, targeting a direct comparison between theory and experiment. In the current model DEP and electro-osmotic forces were considered. Under positive DEP conditions, this resulted in a very good agreement with experiment. Under negative DEP conditions, the agreement is less clear, indicating the importance of other effects. This illustrates the potential of this combined 3D imaging and modeling approach to validate and refine our theoretical understanding of AC field induced colloidal dynamics. This framework is broadly applicable to other complex fluid or microfluidic motion.

cond-mat.soft↗

arXiv2020

Are Shockley-Read-Hall and ABC models valid for lead halide perovskites?

Metal halide perovskites are an important class of emerging semiconductors. Their charge dynamics is poorly understood due to limited knowledge of defect physics and charge recombination mechanisms. Nevertheless, classical ABC and Shockley-Read-Hall (SRH) models are ubiquitously applied to perovskites without considering their validity. Herein, an advanced technique mapping photoluminescence quantum yield (PLQY) as a function of both the excitation pulse energy and repetition frequency is developed and employed to examine the validity of these models. While ABC and SRH fail to explain the charge dynamics in a broad range of conditions, the addition of Auger recombination and trapping to the SRH model enables a quantitative fitting of PLQY maps and low-power PL decay kinetics, and extracting trap concentrations and efficacies. Higher-power PL kinetics requires the inclusion of additional non-linear processes. The PLQY mapping developed herein is suitable for a comprehensive testing of theories and is applicable to any semiconductor.

cond-mat.mtrl-sci↗