Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Q21: Confined Excitons |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Daniel Rizzo, Columbia University Room: Room 213 |
Wednesday, March 8, 2023 3:00PM - 3:12PM |
Q21.00001: Theoretical investigations of optical properties in homo-bilayers transition metal dichalcogenides : stacking effect and electric field tuning Iann C Gerber Stacking 2D materials to build van der Waals heterostructures provides an interesting approach toward creating artificial lattices with desired band structures and possible new functionalities. In transition metal dichalcogenide (TMD) monolayers the optical absorption is strong, but the transition energy cannot be tuned as the neutral exciton has essentially no out-of-plane static electric dipole. In contrast, for homo-bilayers systems hole delocalization over the bilayer is only allowed in 2H stacking and results in strong interlayer exciton absorption and also in a larger A-B exciton separation as compared to 3R bilayers [1,2]. GW+BSE calculation scheme confirm signatures of efficient interlayer coupling for 2H stacking for the MoS2 bilayer case [3], when theoretical investigations of interlayer exciton properties for others TMD bilayers show interesting features. Besides, interlayer exciton transitions are widely tunable in applied electric fields [4] allowing to investigate the interaction between intra and interlayer excitons [5,6]. |
Wednesday, March 8, 2023 3:12PM - 3:24PM |
Q21.00002: Quantum control of interlayer excitons through engineered confinement in MoSe2/WSe2 heterostructures Nadine Leisgang, Andres M Mier Valdivia, Grace Chen, Ryan J Gelly, Kenji Watanabe, Takashi Taniguchi, Hongkun Park, Philip Kim The pursuit of scalable quantum technologies has led to an increasing demand for better control of quantum properties of materials. An exciton, a bound electron-hole pair, constitutes an atomic-like solid-state system which is optically accessible. In two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), electron-hole pairs have particularly large binding energies, such that the excitons are stable even at room temperature. However, as the excitons are charge neutral, traditional depletion traps as employed for 2D electron gases will only provide weak confinement. In this presentation, we focus on MoSe2/WSe2 heterostructures where the bound electrons and holes reside in different layers. As a result of this separation, using the control of thickness of hBN insertion layers, the interlayer excitons are long-lived and have a large permanent dipole moment. Modulating the out-of-plane dipole through the distance of the electron and holes and through an applied electric field, the interlayer excitons can be controlled on a quantum level. The deterministic creation and control over interlayer exciton systems will open up new avenues for quantum applications. |
Wednesday, March 8, 2023 3:24PM - 3:36PM |
Q21.00003: Tunable transport dynamics of layer-hybridized excitons in a natural van Der Waals homobilayer Fedele Tagarelli, Edoardo Lopriore, Daniel Erkensten, Raul Perea-Causin, Samuel Brem, Joakim Hagel, ZHE SUN, Gabriele Pasquale, Kenji Watanabe, Takashi Taniguchi, Ermin Malic, Andras Kis Dipolar interactions are fundamental for the thermalization and condensation of bosonic gases at finite times. Excitons with out-of-plane dipoles feature enhanced inter-particle interactions and longer lifetime, thanks to the dipole alignment and the electron-hole wavefunctions separation. In this work, we achieve control over the layer-hybridization of excitonic species in TMDC bilayers, thus changing the interplay between many-body interactions by means of a vertical electric field. Spatiotemporally-resolved studies allow us to characterize hybrid interlayer exciton (hIX) diffusion, revealing different trends of interactions according to the degree of hybridization. Finally, study the emission quantum yield with respect to excitation power and separate contributions of radiative and nonradiative decay mechanisms. Our work provides fundamental information for the implementation of efficient optoelectronic devices based on exciton transport and for the realization of condensation of bosonic gases. |
Wednesday, March 8, 2023 3:36PM - 3:48PM Author not Attending |
Q21.00004: Seeing quantum correlations through an excitonic lens Sina Zeytinoglu, Valentin Walther Two-dimensional materials provide a fascinating playground for exotic and strongly correlated phenomena of quantum particles. However, current optical experiments that aim to explore the microscopic organization in these materials face an important challenge arising from the optical diffraction limit. The mismatch between the dispersion relation of light and that of the collective many-body excitations of the two-dimensional material constrains the optical measurements to probe matter correlations that fall inside a narrow region in momentum space, the so-called light-cone. Here, we present a protocol for circumventing these constraints through an excitonic lens, which (i) probes with the high-momentum matter correlations of the two-dimensional material through Coulomb interactions, and (ii) implements a Fourier transformation that converts the probe excitonic fields that lie outside of the light-cone to low-momentum fields inside the light-cone. Moreover, the excitonic lens allows correlation functions in momentum space to be read off from the spatial correlations of the output light. We evaluate the performance of our method by numerically simulating an experiment where the signatures of a subwavelength pattern formation can be measured. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q21.00005: Magnetic-field-induced Wigner crystallization of charged interlayer excitons in van der Waals heterostructures Igor V Bondarev, Yu (Yurii) E Lozovik We develop the theory of the magnetic-field-induced Wigner crystallization effect for charged interlayer excitons (CIE) discovered recently in transition-metal-dichalcogenide (TMD) heterobilayers [1]. We derive the ratio of the average potential interaction energy to the average kinetic energy for the many-particle CIE system subjected to the perpendicular magnetic field of an arbitrary strength, analyze the weak and strong field regimes, and discuss the 'cold' crystallization phase transition for the CIE system in the strong field regime [2]. We also generalize the effective g-factor concept previously formulated for interlayer excitons [3], to include the formation of CIEs in electrostatically doped TMD heterobilayers. We show that magnetic-field-induced Wigner crystallization and melting of CIEs can be observed in strong-field magneto-photoluminescence experiments with TMD heterobilayes of systematically varied electron-hole doping concentrations. Our results advance the capabilities of the TMD bilayers as a new family of transdimensional quantum materials. – [1] L.A.Jauregui, et al., Science 366, 870 (2019); [2] I.V.Bondarev and Yu.E.Lozovik, arXiv:2112.13995 (to appear in Communications Physics - Nature); [3] P.Nagler, et al., Nature Communications 8, 1551 (2017). |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q21.00006: Evidence for Exciton Crystals and Quantum Phase Transitions in a 2D Semiconductor Trilayer Yusong Bai, Yiliu Li, Song Liu, Yinjie Guo, Jordan Pack, Jue Wang, Cory R Dean, James C Hone, Xiaoyang Zhu Two-dimensional (2D) transition metal dichalcogenides (TMDC) and their moire interfaces have been demonstrated for correlated electron states, including Mott insulators and electron/hole crystals commensurate with moire superlattices. Here we present spectroscopic evidence for ordered bosons - interlayer exciton crystals in a WSe2/MoSe2/WSe2 trilayer, where the enhanced Coulomb interactions over those in heterobilayers have been predicted to result in exciton ordering. While the dipolar interlayer excitons in the heterobilayer may be ordered by the periodic moire traps, their mutual repulsion results in de-trapping at exciton density larger than 1011 cm-2 to form mobile exciton gases and further to electron-hole plasmas, both accompanied by broadening in photoluminescence (PL) peaks and large increases in mobility. In contrast, ordered interlayer excitons in the trilayer are characterized by negligible mobility and by sharper PL peaks persisting to nex larger than 1012 cm-2. We find that an optically dark state attributed to the predicted quadrupolar exciton crystal transitions to the bright dipolar excitons either with increasing nex or by an applied electric field. These ordered interlayer excitons may serve as models for the exploration of quantum phase transitions and quantum coherent phenomena. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q21.00007: Organic-2D material heterostructures: A promising platform for Excitonic Bose-Einstein Condensation Kanchan A Ulman, Su Ying Quek The exotic state of Bose-Einstein condensation (BEC), generally observed at extremely low temperatures, occurs when all the bosons in the system occupy the ground state. Due to their smaller bosonic mass compared to atoms, Excitons, which are bound electron hole pairs generated in matter by the absorption of photons, can undergo BEC at higher temperatures. However, these excitons need to have long lifetimes, high densities, and small exciton momenta, in order to undergo BEC. While experiments on MoSe2/WSe2 bilayers exhibit excitonic BEC at high temperatures of ~100 K, precise alignment of the layers is required to maintain coherence and hence BEC [1]. Here, we predict that the lowest energy charge transfer excitons in ZnPc-MoS2 organic-2D material heterostructures are ideal candidates for BEC, using first principles GW-BSE calculations [2]. The lowest energy charge transfer excitons in these heterostructures arise from direct transitions, are strongly bound (localized in ~1-2 nm) and have long lifetimes of the order of nanoseconds, and achieving BEC transition temperatures of ~50-100 K. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q21.00008: Magneto-optic characterization of quaternion state in TMD bilayers with metallic screening Qiaochu Wan, Jonathan C Beaumariage, Rui Xue, Li Xiang, Jessica Chisholm, Kenji Watanabe, Takashi Taniguchi, Igor V Bondarev, Dmitry Smirnov, David W Snoke, Zheng Sun Van der Waals (vdW) heterostructures have served as a new platform for exploring novel higher-order excitonic bound states including trions, biexictions and even “hexcitons” and “oxcitons.” [1] In our recent experiments [2], we observed evidence for a new bound excitonic state in a bilayer structure: two free carriers bound to an exciton, forming a doubly charged “quaternion.” The key feature of this state is that the metallic screening helps to reduce the overall repulsion of like charges. We have conducted many controlled experiments with different designs to show that the quaternion state only exist when the full structure is in place, including the bilayer and the metallic layer under it. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q21.00009: Engineering strain and interlayer excitons of 2D materials via lithographically engraved hexagonal boron nitride substrates Yu-Chiang Hsieh, Zhen-You Lin, Shin-Ji Fung, Sheng-Chin Ho, Siang-Ping Hong, Sheng-Zhu Ho, Chiu-Hua Huang, Takashi Taniguchi, Kenji Watanabe, Yi-Chun Chen, Chung-Lin Wu, Tse-Ming Chen Strain engineering has recently emerged as a viable option to modify the electronic, optical, and magnetic properties of two-dimensional (2D) materials, e.g., by introducing a giant pseudo-magnetic field and unconventional Hall effects [1,2]. However, it remains challenging to arbitrarily control the strain distribution and magnitude, limiting the extent to which straintronics can operate and advance. Here, by using atomic-scale etching to create any desired surface topography or nanostructures in hexagonal boron nitride (hBN) substrates, we can arbitrarily manipulate the strain of molybdenum disulfide (MoS2) flakes placed onto the hBN. The phonon and exciton emissions are shown to vary in accordance with our strain (structure) designs, enabling us to create arbitrary phonon vibration and photoluminescence color images. Moreover, the strain engineering is found to substantially enhance the interlayer excitons. Such an enhancement is significant because the conventional uniaxial strain does not affect the oscillator strength of interlayer excitons. The proof-of-concept demonstration of our strain engineering may well open new opportunities for 2D straintronics and optoelectronics. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q21.00010: Creating lateral quantum wells in monolayer semiconductors by an electrostatic confinement mechanism Jenny Hu, Etienne LORCHAT, Xueqi Chen, Elie Vandoolaeghe, Puneet A Murthy, Tony F Heinz, Thibault Chervy Excitons in monolayer TMDC semiconductors have proven to be an excellent platform for revealing much new physics of correlated electronic states and also offer promise for next-generation optoelectronic devices. Lateral confinement, combined with the natural vertical confinement of 2D materials, provides new routes to modify and control excitons, including the possibility of creating arbitrarily placed quantum emitters. Various approaches, such as localized strain and moiré potentials, have been successfully developed. Recent studies have also revealed that excitons in monolayer MoSe2 can be confined effectively at the edge of the top gate in a dual-gated device structure. [1] This confinement results from the spatially localized parallel component of the electric field, as well as from the influence of doping. As a purely electrostatic mechanism, the confinement can easily be switched on or off, as well as tuned continuously. Here we employ this confinement mechanism to study the interaction between excitons confined by the edges of two parallel, closely spaced electrostatic gates. We demonstrate the independent tunability of two sets of 1D confined states using optical absorption and emission spectroscopy. We further show that a single quantum well for excitons can be formed a result of the two edges for an appropriate geometry. These results advance our capabilities for the manipulation and hybridization of confined excitons, as well as for the creation of large, degenerate quantum emitter arrays. [1] Thureja, D., Imamoglu, A., Smolenski, T. et al. Electrically tunable quantum confinement of neutral excitons. Nature 606, 298–304 (2022). |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q21.00011: Tunable quantum traps for excitons in 2D semiconductors Puneet A. Murthy, Deepankur Thureja, Atac Imamoglu, Tomasz Smolenski, Ivan Amelio, Alexander Popert, Thibault Chervy, David J Norris, Martin Kroner The realization of fully tunable quantum emitters in solid state systems has been an outstanding goal of optoelectronics and quantum photonics. In this talk, we will discuss our recent experimental results demonstrating quantum confinement of neutral excitons in monolayer Transition metal dichalcogenides with full electrical control [1]. We show that excitons can be quantum confined to below 10 nanometers using strong in-plane electric fields that induce a dc Stark shift. Using optical spectroscopy, we observe discrete excitonic states below the continuum that originate from the quantization of the motional states of excitons due to confinement. Furthermore, through magneto-optical measurements, we find that the electric field induced confinement has a dramatic influence also on the relative wavefunction of excitons. We anticipate that our quantum confinement approach may provide a scalable platform for arrays of identical single photon sources and constitute building blocks of strongly correlated photonic many-body systems. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q21.00012: Electrostatic single exciton trapping in a 2D semiconductor heterostructure using nanopatterned graphene Daniel N Shanks, Fateme Mahdikhanysarvejahany, David G Mandrus, Michael Koehler, Takashi Taniguchi, Kenji Watanabe, Brian J LeRoy, John Schaibley Interlayer excitons (IXs) in 2D semiconductors have long lifetimes and spin-valley coupled physics, with a long-standing goal of single exciton trapping for quantum applications. In this work, we use a nano-patterned graphene gate to create an electrostatic IX trap. In photoluminescence measurements, we observe narrow linewidth emission, which is a signature of strong spatial confinement, and a unique power-dependent blue-shift of IX energy, with jumps between discrete emission energies. We attribute these jumps to quantized increases of the number occupancy of IXs within the trap. We compare these results to a theoretical model to assign the lowest energy emission line to single IX recombination, indicating that we can create a population of a single exciton within our trap using low laser excitation power. These traps are advantageous over other trapping methods involving strain or moiré potentials due to their deterministic lithographically defined process, 100 meV energy tunability by applied gate voltage, and scalability to create large arrays of single quantum emitters with controllable placement. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q21.00013: Collective optical emission by dark moire excitons Benyamin Remez, Nigel R Cooper In two-dimensional Van der Waals heterostructures, tightly bound and long-lived interlayer excitons allow us to explore rich many-body physics. Particularly compelling are twisted bilayers, where a trapping moire potential promotes strong interactions and correlated phases like exciton condensates. Yet the twist-induced indirect band gap renders these excitons momentum-dark, leading to an optically inaccessible dark condensate. We show that the strong interactions drive an emergent emission process where the recombination recoil is absorbed by longitudinal collective modes – a kind of excitonic Mossbauer effect. This many-body "leaky emission" dominates the condensate optical signature at low temperatures. Strong interactions and a valley degree of freedom may lead to additional collective phenomena, such as excitonic density ordering. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q21.00014: Programmable nano-wrinkle induced room-temperature exciton localization in monolayer WSe2 Emanuil S Yanev, Thomas P Darlington, Matthew Strasbourg, Song Liu, Nicholas Borys, James C Hone, P. James Schuck Localized states in two-dimensional transition metal dichalcogenides (TMDCs) have been the subject of intense study recently, largely due to the exciting prospect of their application in quantum information science. Despite the rapidly growing knowledge surrounding these emitters, their exact microscopic nature is still not fully understood. A popular approach for exploring quantum emission from these materials has been the use of pillars, particles, or other nanostructures to induce local strain. However, directly probing local correlations between strain and quantum emission has proven challenging due to the requirement for sub-diffraction spatial resolution. Motivated by recent theoretical and experimental evidence suggesting that nanoscale wrinkles are responsible for localized emission1, here we focus on intentionally inducing wrinkles and mapping their photoluminescence (PL) using nano-optical techniques. We show that long-range wrinkle direction is controllable with patterned array design. Meanwhile, the strain environment around individual stressors is often highly heterogeneous due to the presence of ultrafine wrinkles that are less deterministic. Detailed PL maps reveal a wide range of low-energy emission peaks originating from these ultrafine wrinkles, and that the states can be tightly confined to regions < 10 nm, even at room temperature. This is promising evidence that, under the right conditions, room temperature quantum emission could be achievable in 2D TMDC systems. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700