Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y72: Optical and Photonic Properties of 2D MaterialsFocus Recordings Available
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Sponsoring Units: DMP Chair: Hanyu Zhu, Rice University Room: Hyatt Regency Hotel -Jackson Park D |
Friday, March 18, 2022 8:00AM - 8:36AM |
Y72.00001: Exciton manipulation and transport in 2D semiconductor heterostructure devices Invited Speaker: Andras Kis Long-lived interlayer excitons in van der Waals heterostructures based on TMDCs have emerged as a promising platform for realizing solid-state devices based on the electrical control of exciton transport. I will show here how by using van der Waals heterostructures, we can realize excitonic transistors with switching action, confinement and control over diffusion length at room temperature in a reconfigurable potential landscape. Heterostructures with long-wavelength moiré potentials on the other hand, allow addressing local areas of he heterostructure with different local symmetries and optical selection rules. By using externally applied electrical fields, we can control their relative intensities and polarization by different regions in the moiré pattern, characterized by different local symmetries and optical selection rules. Our more advanced excitonic devices with an engineered moiré interaction now also offer the way to manipulate the motion of valley (spin) polarized excitons. By using spatial and time-resolved photoluminescence imaging, we observe the dynamics of exciton transport, enabling a direct estimation of the exciton mobility. The presence of interactions significantly modifies the diffusive transport of excitons, effectively acting as a source of drift force and enhancing the diffusion coefficient by one order of magnitude. The repulsive dipolar interactions combined with the electrical control of interlayer excitons opens up appealing new perspectives for excitonic devices. |
Friday, March 18, 2022 8:36AM - 9:12AM |
Y72.00002: Optical spectroscopy of novel correlated states in semiconducting moiré superlattices Invited Speaker: Chun Hung Lui Monolayer transition metal dichalcogenides (TMDs, e.g. MoSe2, WS2, and WSe2) exhibit remarkable optical, optoelectronic, excitonic, and valleytronic properties for novel applications. When two TMD monolayers are stacked together, the mismatch of their lattice constants and/or orientation angles can produce moiré superlattices with substantial confinement and correlation effect. In this talk, I will present our investigations of the novel correlated states in TMD moiré superlattices by optical spectroscopy. We observe optical signatures of trions confined by the moiré potential in the WSe2/MoSe2 moiré superlattices. Such moiré trions exhibit sharp emission lines and complex charge-density dependence, in stark contrast to the behavior of conventional trions. Moreover, we investigate the optical signatures of correlated electronic phases at fractional fillings of the WSe2/WS2 moiré superlattices. These correlated electronic phases can couple to the trion states to modulate the spectra and valley polarization of the trions. Our results demonstrate moiré superlattices as an excellent platform to explore novel correlated phenomena. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y72.00003: Directional transport of interlayer excitons in MoSe2-WSe2 heterostructures Daniel N Shanks, Michael R Koehler, David G Mandrus, Takashi Taniguchi, Kenji Watanabe, Brian J LeRoy, John Schaibley Control of interlayer excitons (IXs) in MoSe2-WSe2 heterostructures has recently been of significant interest, with promising applications to quantum technologies. Previous studies have shown that IXs can be localized by the moiré potential or electrostatic trapping, and that suppression of the moiré potential through an hBN separating layer allows for micron scale diffusion of IXs. It has also been shown that the spatial diffusion of excitons can be controlled using the interaction between the permanent dipole moment of the IX and patterned graphene gates to create a spatially varying electric field, but such studies have been limited to micron-scale gate structures. In this presentation, we show that exciton diffusion can be controlled on a much smaller scale using nanopatterned graphene gates. Specifically, we show that using a triangular graphene etch, we can create unidirectional diffusion of IXs, i.e., an excitonic diode, which can be used in technologies based on excitons in TMD heterostructures. Additionally, we have the potential to study exciton dynamics as a function of continuously varying in-plane potentials with the goal of realizing excitonic circuits. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y72.00004: Room temperature exciton switch Kanak Datta, Zidong Li, Takashi Taniguchi, Kenji Watanabe, Parag B Deotare |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y72.00005: On-chip integration of site controlled hBN quantum emitters in a low-emission silicon nitride platform Shaimaa Azzam, Kamyar Parto, Nicholas Lewis, Galan Moody Single-photon emitters hosted by atomically thin two-dimensional (2D) materials have proven very attractive with high brightness, ambient condition operation, and site-specific engineering. Integrating single photons in 2D hosts with photonic circuits is a central building block for quantum photonics to enhance spectral properties, light-matter interactions, and indistinguishability. Here, we present novel prototypes for integrating room-temperature single-photon emitters in hexagonal boron nitride (hBN) to low-loss, low-emission silicon nitride photonic integrated circuits. Our platform features an optimized approach that couples more than 50% of the generated single-photons to the waveguide's optical mode, microring resonators for Purcell enhancement, and chip-to-fiber coupling. Additionally, a precise alignment of the quantum defects is achieved by combining two sets of global and local alignment marks enabling diffraction-limited accuracy of their positioning on the target chip. This integrated platform is a vital step towards scalable photonic quantum circuits. In the future, the Stark effect can be exploited for efficient spectral tunability, enabling a deterministic control of the single photon's spatio-temporal and spectral properties and their coupling to resonators. |
Friday, March 18, 2022 9:48AM - 10:00AM |
Y72.00006: Photoluminescence quenching in mixed-dimensional heterostructures from non-covalent functionalization of monolayer WSe2 via aryl diazonium chemistry Iqbal B Utama, Hongfei Zeng, Anushka Dasgupta, Tumpa Sadhukhan, S. Carin Gavin, Dmitry Lebedev, Wei Wang, Jia-Shiang Chen, Kenji Watanabe, Takashi Taniguchi, Tobin J Marks, Xuedan Ma, George C Schatz, Nathaniel P Stern, Mark C Hersam Monolayer WSe2 is an important member of the 2D layered materials family due to its valley physics and excitonic properties with potential applications in quantum optoelectronics. Chemical functionalization of monolayer WSe2 has been performed with nitrobenzenediazonium (4-NBD), resulting in surface functionalization with nitrophenyl oligomers that induces hole doping of the monolayer. Here, we discuss the optical properties of 4-NBD-treated WSe2 at the limit of full coverage of the nitrophenyl oligomers. In ambient conditions, we observe strong photoluminescence (PL) quenching and redshifting. Moreover, the PL at low temperature shows a nearly complete quenching of the exciton fine structures beyond the neutral exciton. This quenching effect is reversible upon oligomer removal and can be attributed to processes beyond hole doping. X-ray photoelectron spectroscopy reveals that the functionalization is non-covalent, and further elucidates the mixed-dimensional heterojunction formation that contributes to PL quenching in a manner consistent with first-principles calculations. Overall, these results demonstrate that diazonium functionalization is an effective pathway for modifying the optical properties of monolayer WSe2. |
Friday, March 18, 2022 10:00AM - 10:12AM |
Y72.00007: Theoretical study of the enhancement of spontaneous two-photon emission in Er3+ by graphene plasmons Colin Whisler, Gregory R Holdman, Victor W Brar, Deniz D Yavuz Spontaneous two-photon emission (STPE) occurs when an excited emitter decays through the spontaneous production of two photons rather than one photon. This process provides an intriguing potential source of entangled photons with a broad distribution of frequencies. In most cases, the rate of STPE is dramatically slower than that of single-photon emission; however, it has recently been predicted that, for hydrogenic atoms, the optical surface waves in 2D materials could be used to significantly increase the STPE rate. Here we investigate the efficiency of this process for the 4I13/2 → 4I15/2 transition of trivalent erbium, which occurs around 1550 nm and is used in telecommunications. We perform a comprehensive calculation of all matrix elements involved in the STPE process and couple this with finite-difference time-domain simulations of the emission rate enhancement of an erbium emitter placed near a graphene sheet. We derive experimental conditions whereby graphene plasmons augment the STPE rates to become comparable to single-photon transition rates. Furthermore, we show that patterning the graphene into an array of nanoribbons allows the radiative two-photon emission to become strongly enhanced when the graphene’s Fermi energy is tuned to the proper resonance value. |
Friday, March 18, 2022 10:12AM - 10:24AM |
Y72.00008: Unraveling heat transport and dissipation in suspended MoSe2 crystals from bulk to monolayer Matthieu J Verstraete, Zeila Zanolli, Roberta Farris, Olle Hellman, Klaas-Jan Tielrooij, Pablo Ordejon Understanding thermal transport in layered transition metal dichalcogenide (TMD) crystals is crucial for a myriad of applications exploiting these materials. Despite significant efforts, several basic thermal transport properties of TMDs are currently not well understood. Here, we present a combined experimental-theoretical study of the intrinsic lattice thermal conductivity of the representative TMD MoSe2, focusing on the effect of material thickness and the material's environment. We use Raman thermometry measurements on suspended crystals, where we identify and eliminate crucial artefacts, and perform ab initiosimulations with phonons at finite, rather than zero, temperature. We find that phonon dispersions and lifetimes change strongly with thickness, yet (sub)nanometer thin TMD films exhibit a similar in-plane thermal conductivity (∼20~Wm−1K−1) as bulk crystals (∼40~Wm−1K−1). This is the result of compensating phonon contributions, in particular low-frequency modes with a surprisingly long mean free path of several micrometers that contribute significantly to thermal transport for monolayers. We furthermore demonstrate that out-of-plane heat dissipation to air is remarkably efficient, in particular for the thinnest crystals. These results are crucial for the design of TMD-based applications in thermal management, thermoelectrics and (opto)electronics. |
Friday, March 18, 2022 10:24AM - 10:36AM |
Y72.00009: Control of Thermal Conductance across Vertically Stacked Two-Dimensional van der Waals Materials via Interfacial Engineering Kazuhiro Yanagi, Wenyu Yuan, Kan Ueji, Takashi Yagi, Takahiko Endo, Hong E Lim, Yasumitsu Miyata, Yohei Yomogida A comprehensive understanding of the roles of various nanointerfaces in thermal transport is of critical significance but remains challenging. A two-dimensional van der Waals (vdW) heterostructure with tunable interface lattice mismatch provides an ideal platform to explore the correlation between thermal properties and nanointerfaces and achieve controllable tuning of heat flow. Here, we demonstrate that interfacial engineering is an efficient strategy to tune thermal transport via systematic investigation of the thermal conductance (G) across a series of large-area four-layer stacked vdW materials using an improved polyethylene glycol-assisted time-domain thermoreflectance method. Owing to its rich interfacial mismatch and weak interfacial coupling, the vertically stacked MoSe2-MoS2-MoSe2-MoS2 heterostructure demonstrates the lowest G of 1.5 MW m-2 K-1 among all vdW structures. A roadmap to tune G via homointerfacial mismatch, interfacial coupling, and heterointerfacial mismatch is further demonstrated for thermal tuning.The design principle is promising for application in other areas, such as the electrical tuning of energy storage and conversion and the thermoelectricity tuning of thermoelectronics. |
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