arXiv subjects

Varun-Varma Pusapati

Publications and source records attributed to Varun-Varma Pusapati.

3 recordsLinked to original sources

arXiv2020

Plasmonic antenna coupling to hyperbolic phonon-polaritons for sensitive and fast mid-infrared photodetection with graphene

Integrating and manipulating the nano-optoelectronic properties of Van der Waals heterostructures can enable unprecedented platforms for photodetection and sensing. The main challenge of infrared photodetectors is to funnel the light into a small nanoscale active area and efficiently convert it into an electrical signal. Here, we overcome all of those challenges in one device, by efficient coupling of a plasmonic antenna to hyperbolic phonon-polaritons in hexagonal-BN to highly concentrate mid-infrared light into a graphene pn-junction. We balance the interplay of the absorption, electrical and thermal conductivity of graphene via the device geometry. This novel approach yields remarkable device performance featuring room temperature high sensitivity (NEP of 82 pW-per-square-root-Hz) and fast rise time of 17 nanoseconds (setup-limited), among others, hence achieving a combination currently not present in the state-of-the-art graphene and commercial mid-infrared detectors. We also develop a multiphysics model that shows excellent quantitative agreement with our experimental results and reveals the different contributions to our photoresponse, thus paving the way for further improvement of these types of photodetectors even beyond mid-infrared range.

cond-mat.mes-hall↗

arXiv2020

Far-field Excitation of Single Graphene Plasmon Cavities with Ultra-compressed Mode-volumes

Acoustic-graphene-plasmons (AGPs) are highly confined electromagnetic modes, carrying large momentum and low loss in the mid-infrared/Terahertz spectra. Owing to their ability to confine light to extremely small dimensions, they bear great potential for ultra-strong light-matter interactions in this long wavelength regime, where molecular fingerprints reside. However, until now AGPs have been restricted to micron-scale areas, reducing their confinement potential by several orders-of-magnitude. Here, by utilizing a new type of graphene-based magnetic-resonance, we realize single, nanometric-scale AGP cavities, reaching record-breaking mode-volume confinement factors of $\thicksim5\cdot10^{-10}$. This AGP cavity acts as a mid-infrared nanoantenna, which is efficiently excited from the far-field, and electrically tuneble over an ultra-broadband spectrum. Our approach provides a new platform for studying ultra-strong-coupling phenomena, such as chemical manipulation via vibrational-strong-coupling, and a path to efficient detectors and sensors, in this challenging spectral range.

physics.optics↗

arXiv2019

Near-unity light absorption in a monolayer WS2 van der Waals heterostructure cavity

Excitons in monolayer transition-metal-dichalcogenides (TMDs) dominate their optical response and exhibit strong light-matter interactions with lifetime-limited emission. While various approaches have been applied to enhance light-exciton interactions in TMDs, the achieved strength have been far below unity, and a complete picture of its underlying physical mechanisms and fundamental limits has not been provided. Here, we introduce a TMD-based van der Waals heterostructure cavity that provides near-unity excitonic absorption, and emission of excitonic complexes that are observed at ultra-low excitation powers. Our results are in full agreement with a quantum theoretical framework introduced to describe the light-exciton-cavity interaction. We find that the subtle interplay between the radiative, non-radiative and dephasing decay rates plays a crucial role, and unveil a universal absorption law for excitons in 2D systems. This enhanced light-exciton interaction provides a platform for studying excitonic phase-transitions and quantum nonlinearities and enables new possibilities for 2D semiconductor-based optoelectronic devices.

physics.optics↗