arXiv subjects

Anthony Nickolas Vamivakas

Publications and source records attributed to Anthony Nickolas Vamivakas.

5 recordsLinked to original sources

arXiv2026

Highly nonlinear Moiré exciton and trion polaritons

Moiré multi-layers of transition metal dichalcogenides have been shown to exhibit optical responses that are endowed with a richness that is absent in single monolayers. Much of this can be attributed to the Moiré superlattice that modulates the electronic landscape of these heterostructures. Strongly coupled layer-hybridized excitons in $\text{MoSe}_2 / \text{WS}_2$ heterobilayers have been shown to exhibit enhanced optical nonlinearities. In this work we strongly couple layer hybridized excitons and trions in n-doped $\text{MoSe}_2 / \text{WS}_2$ heterobilayers inside an optical microcavity. We find that the additional Lindhard screening from dopant electrons and the formation of trions result in a strikingly non-monotonic nonlinear response. The absence of electron capture in the Moiré superlattice plays a crucial role, promising very large second-order nonlinearities. In this work, trion polaritons manifest as high velocity hot polaritons, reaching nominal diffusion lengths approaching 100 microns.

cond-mat.mes-hall↗

arXiv2025

Diffusion of valley-coherent dark excitons in a high-angle incommensurate Moiré homobilayer

The last few years have witnessed a surge in interest and research efforts in the field of twistronics, especially in low-angle twisted bilayers of transition metal dichalocogenides. These novel material platforms have been demonstrated to host periodic arrays of excitonic quantum emitters, interlayer excitons with long lifetimes, and exotic many-body states. While much remains to be known and understood about these heterostructures, the field of large-angle, incommensurate bilayers is even less explored. At twist angles larger than a few degrees, the presence of periodicity in these bilayers becomes chaotic, making the systems essentially aperiodic and incommensurate in nature due to the limitations of fabrication techniques. In this work, we demonstrate the emergence of a brightened dark intralayer exciton in twisted n-doped molybdenum diselenide homobilayer. We show that this dark exciton diffuses across the excitation spot more efficiently as compared to bright trions or excitons, reaching diffusion lengths greater than 4 microns. Temperature-dependent spectra provide corroborative evidence and reveal a brightened dark trion. Almost inexplicably, this dark exciton showcases a robust valley coherence, which we attribute to a small mixing of the spin-resolved conduction bands due to an absence of out-of-plane reflection symmetry arising from a strong dielectric contrast. Our results reveal some of the richness of the physics of these large-angle systems while uncovering new opportunities for valleytronic devices that may utilize these more valley-robust "mixed" dark excitons.

cond-mat.mes-hall↗

arXiv2023

Interplay of trapped species and absence of electron capture in Moiré heterobilayers

Moiré heterobilayers host interlayer excitons in a natural, periodic array of trapping potentials. Recent work has elucidated the structure of the trapped interlayer excitons and the nature of photoluminescence (PL) from trapped and itinerant charged complexes such as interlayer trions in these structures. In this paper, our results serve to add to the understanding of the nature of PL emission and explain its characteristic blueshift with increasing carrier density, along with demonstrating a significant difference between the interlayer exciton-trion conversion efficiency as compared to both localized and itinerant intra-layer species in conventional monolayers. Our results show the absence of optical generation of trions in these materials, which we suggest arises from the highly localized, near sub-nm confinement of trapped species in these Moiré potentials.

cond-mat.mtrl-sci↗

arXiv2011

Sub-Natural Linewidth Single Photons from a Quantum Dot

The observation of quantum dot resonance fluorescence enabled a new solid-state approach to generating single photons with a bandwidth almost as narrow as the natural linewidth of a quantum dot transition. Here, we operate in the Heitler regime of resonance fluorescence to generate sub-natural linewidth and high-coherence quantum light from a single quantum dot. The measured single-photon bandwidth exhibits a 30-fold reduction with respect to the radiative linewidth of the QD transition and the single photons exhibit coherence properties inherited from the excitation laser. In contrast, intensity-correlation measurements reveal that this photon source maintains a high degree of antibunching behaviour on the order of the transition lifetime with vanishing two-photon scattering probability. This light source will find immediate applications in quantum cryptography, measurement-based quantum computing and, in particular, deterministic generation of high-fidelity distributed entanglement among independent and even disparate quantum systems.

quant-ph↗

arXiv2006

Phonon Dispersion in Chiral Single Wall Carbon Nanotubes

The phonon dispersion of chiral single wall carbon nanotubes has been obtained from $6\times 6$ dyanimic matrix. The present manuscript is the extension of G. D. Mahan and Gun Sang Jeon's work on armchair and zigzag nanotubes. [see P. R. B., {\bf 70}, 075405 (2004)]. We use spring and mass model with the proper phonon potential suggested by \cite{M2}. We can calculate the dispersion of single wall carbon nanotubes near $Γ$ point with arbitrary chirality. The results are compatible with Mahan et. al's results for armchair and zigzag SWNTs.

cond-mat.mes-hall↗