Maryland Shared Open Access Repository

MD-SOAR is a shared digital repository platform for twelve colleges and universities in Maryland. It is currently funded by the University System of Maryland and Affiliated Institutions (USMAI) Library Consortium (usmai.org) and other participating partner institutions. MD-SOAR is jointly governed by all participating libraries, who have agreed to share policies and practices that are necessary and appropriate for the shared platform. Within this broad framework, each library provides customized repository services and collections that meet local institutional needs. Please follow the links below to learn more about each library's repository services and collections.

 

Browse

Communities and Collections | By Issue Date | Author | Titles | Subjects | Type

Submit

Institutions in MD-SOAR

Select a community to browse its collections.

Recent Submissions

Thumbnail Image
Item
Chiral and quantum optics in 2D platforms
(SPIE, 2024-03-13) Suarez-Forero, Daniel G.; Ni, Ruihao; Sarkar, Supratik; Mehrabad, Mahmoud Jalali; Hafezi, Mohammad; Zhou, You
A fundamental requirement for photonic technologies is the ability to control the confinement and propagation of light. Widely utilized platforms include 2D optical microcavities in which electromagnetic waves are confined between either metallic or multi-layer distributed Bragg reflector dielectric mirrors. However, the fabrication complexities of thick Bragg reflectors and high losses in metallic mirrors have motivated the quest for efficient and compact mirrors. Recently, 2D transition metal dichalcogenides hosting tightly bound excitons with high optical quality were shown as promising atomically thin mirrors (a, b). In this work, we propose and experimentally demonstrate a sub-wavelength 2D nanocavity using two atomically thin mirrors (c-f). Remarkably, we show how the excitonic nature of the mirrors enables the formation of chiral and tunable cavity modes upon the application of an external magnetic field (g). Our work establishes a new regime for engineering intrinsically chiral sub-wavelength optical cavities and opens avenues for realizing spin-photon interfaces and exploring chiral many-body cavity electrodynamics.
Thumbnail Image
Item
Excitonic Mott insulator in a Bose-Fermi-Hubbard system of moiré WS₂/WSe₂ heterobilayer
(Nature, 2024-03-14) Gao, Beini; Suarez-Forero, Daniel G.; Sarkar, Supratik; Huang, Tsung-Sheng; Session, Deric; Mehrabad, Mahmoud Jalali; Ni, Ruihao; Xie, Ming; Upadhyay, Pranshoo; Vannucci, Jonathan; Mittal, Sunil; Watanabe, Kenji; Taniguchi, Takashi; Imamoglu, Atac; Zhou, You; Hafezi, Mohammad
Understanding the Hubbard model is crucial for investigating various quantum many-body states and its fermionic and bosonic versions have been largely realized separately. Recently, transition metal dichalcogenides heterobilayers have emerged as a promising platform for simulating the rich physics of the Hubbard model. In this work, we explore the interplay between fermionic and bosonic populations, using a WS₂/WSe₂ heterobilayer device that hosts this hybrid particle density. We independently tune the fermionic and bosonic populations by electronic doping and optical injection of electron-hole pairs, respectively. This enables us to form strongly interacting excitons that are manifested in a large energy gap in the photoluminescence spectrum. The incompressibility of excitons is further corroborated by observing a suppression of exciton diffusion with increasing pump intensity, as opposed to the expected behavior of a weakly interacting gas of bosons, suggesting the formation of a bosonic Mott insulator. We explain our observations using a two-band model including phase space filling. Our system provides a controllable approach to the exploration of quantum many-body effects in the generalized Bose-Fermi-Hubbard model.
Thumbnail Image
Item
Observation of topological frequency combs
( American Association for the Advancement of Science, 2024-06-20) Flower, Christopher J.; Jalali Mehrabad, Mahmoud; Xu, Lida; Moille, Gregory; Suarez-Forero, Daniel G.; Oğulcan Örsel; Bahl, Gaurav; Chembo, Yanne; Srinivasan, Kartik; Mittal, Sunil; Hafezi, Mohammad
On-chip generation of optical frequency combs using nonlinear ring resonators has enabled numerous applications of combs that were otherwise limited to mode-locked lasers. Nevertheless, on-chip frequency combs have relied predominantly on single-ring resonators. In this study, we experimentally demonstrate the generation of a novel class of frequency combs, the topological frequency combs, in a two-dimensional lattice of hundreds of ring resonators that hosts fabrication-robust topological edge states with linear dispersion. By pumping these edge states, we demonstrate the generation of a nested frequency comb that shows oscillation of multiple edge state resonances across ≈40 longitudinal modes and is spatially confined at the lattice edge. Our results provide an opportunity to explore the interplay between topological physics and nonlinear frequency comb generation in a commercially available nanophotonic platform.
Thumbnail Image
Item
Giant enhancement of exciton diffusion near an electronic Mott insulator
(2024-09-27) Upadhyay, Pranshoo; Suarez-Forero, Daniel G.; Huang, Tsung-Sheng; Mehrabad, Mahmoud Jalali; Gao, Beini; Sarkar, Supratik; Session, Deric; Watanabe, Kenji; Taniguchi, Takashi; Zhou, You; Knap, Michael; Hafezi, Mohammad
Bose-Fermi mixtures naturally appear in various physical systems. In semiconductor heterostructures, such mixtures can be realized, with bosons as excitons and fermions as dopant charges. However, the complexity of these hybrid systems challenges the comprehension of the mechanisms that determine physical properties such as mobility. In this study, we investigate interlayer exciton diffusion in an H-stacked WSe₂/WS₂ heterobilayer. Our measurements are performed in the ultra-low exciton density regime at low temperatures to examine how the presence of charges affects exciton mobility. Remarkably, for charge doping near the Mott insulator phase, we observe a giant enhancement of exciton diffusion of three orders of magnitude compared to charge neutrality. We attribute this observation to mobile valence holes, which experience a suppressed moiré potential due to the electronic charge order in the conduction band, and recombine with any conduction electron in a non-monogamous manner. This new mechanism emerges for sufficiently large fillings in the vicinity of correlated generalized Wigner crystal and Mott insulating states. Our results demonstrate the potential to characterize correlated electron states through exciton diffusion and provide insights into the rich interplay of bosons and fermions in semiconductor heterostructures.
Thumbnail Image
Item
X-ray outburst of a radio-loud quasar
(The Astronomer's Telegram, 2025-04-23) Orish, M.; Behar, E.; Nagashima, N.; Pottschmidt, Katja; et al
We report that the XRISM/XTEND Transient Search source XRISM J1826-3651, observed on 2025-04-12 and reported in ATel #17145 was observed again with the Swift X-Ray Telescope (XRT) on 2025-04-22 for a total (non continuous) on-source time of 2642 s. The source is still X-ray luminous, and was detected with a count rate 0.022±0.004 cts/s at this position: alpha=18 26 08.16 and delta=-36 50 46.8, with a position uncertainty of 4.2 arcseconds. The spectrum is relatively hard and can be fitted with a power law, with photon index 1.9(+0.8/-0.6), absorbing column density N(H)=2.2(+3.6/-2.1) cm⁻², absorbed flux of 1.0±0.5 x 10⁻¹² erg/cm/⁻²/s, and unabsorbed flux ~1.3 x 10⁻¹² erg/cm⁻²/s. The most likely counterpart is the radio-loud quasar and blazar 1WGA J1826.1-3650 at redshift z=0.888 (Veron Cetty et al. 2010, A&A, 518, 10), which also corresponds to GAIA source 6728071805422016896, at 2.9 arcsec from the Swift XRT position. This object was serendipitously observed with ROSAT in X-rays as 1WGA J1826.1-3650 at comparable luminosity in 1992 March, so this is not the first X-ray active state, but X-ray observations in the intervening time are missing.