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Resolving High-Energy States of Interlayer Excitons in MoSe$_2$/WSe$_2$ Heterostructures
Authors:
Chirag Chandrakant Palekar,
Paulo E. Faria Junior,
Tobias Manthei,
Maximilian Nagel,
Bhabani Sankar Sahoo,
Shachi Machchhar,
Imad Limame,
Martin Podhorský,
Jaroslav Fabian,
Bárbara Rosa,
Stephan Reitzenstein
Abstract:
High-energy states of interlayer excitons (IXs) in van der Waals heterostructures remain largely unexplored despite their importance for understanding many-body interactions and nonlinear optical phenomena. Here, we use photoluminescence excitation (PLE) spectroscopy to resolve a Rydberg-like series of excited IX states in MoSe$_2$/WSe$_2$ heterostructures. We observe multiple PLE resonances below…
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High-energy states of interlayer excitons (IXs) in van der Waals heterostructures remain largely unexplored despite their importance for understanding many-body interactions and nonlinear optical phenomena. Here, we use photoluminescence excitation (PLE) spectroscopy to resolve a Rydberg-like series of excited IX states in MoSe$_2$/WSe$_2$ heterostructures. We observe multiple PLE resonances below the intralayer exciton energies, which we assign to the 2s-, 3s-, and 4s-like states of the IXs. These resonances are consistently observed across heterostructures with different twist angles, indicating that the high-energy state spectrum is only weakly affected by the twist angle. Wannier-exciton calculations incorporating screened Coulomb interactions reproduce the overall energy scale and qualitative trends of the measured Rydberg-like series, supporting the assignment of the observed resonances. Our findings demonstrate that PLE provides direct experimental access to the previously unexplored high-energy IX states in van der Waals heterostructures.
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Submitted 3 August, 2026;
originally announced August 2026.
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An integrated all-van der Waals nanobeam laser
Authors:
Aris Koulas-Simos,
Pietro Metuh,
Athanasios Paralikis,
Kartik Gaur,
Maximilian Klonz,
Imad Limame,
Bárbara L. T. Rosa,
Chirag C. Palekar,
Battulga Munkhbat,
Stephan Reitzenstein
Abstract:
Transition-metal dichalcogenides offer a promising platform for integrated coherent light sources, yet lasing has largely relied on hybrid photonic architectures without direct quantum-optical verification. Here, we demonstrate an all-van der Waals (all-vdW) high-$β$ nanobeam laser based on a WS$_2$/MoSe$_2$/WS$_{2}$ heterostructure, with the MoSe$_2$ monolayer directly integrated in the WS$_{2}$-…
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Transition-metal dichalcogenides offer a promising platform for integrated coherent light sources, yet lasing has largely relied on hybrid photonic architectures without direct quantum-optical verification. Here, we demonstrate an all-van der Waals (all-vdW) high-$β$ nanobeam laser based on a WS$_2$/MoSe$_2$/WS$_{2}$ heterostructure, with the MoSe$_2$ monolayer directly integrated in the WS$_{2}$-based optical resonator for optimal gain-mode overlap. The devices exhibit efficient exciton-cavity coupling at cryogenic temperatures, strongly directional and linearly polarized emission, soft nonlinear input-output characteristics and linewidth narrowing, enabling lasing operation with $β$ near unity. Excitation-power-dependent photon-autocorrelation measurements reveal a transition from thermal to Poissonian photon statistics, with $g_{\mathrm{peak}}^{(2)}(0)$ decreasing from $(1.28\,\pm\,0.09)$ near threshold to $(1.07\,\pm\,0.07)$ above threshold, directly verifying lasing operation. Furthermore, temporal broadening of the autocorrelation uncovers fluctuation-dominated lasing dynamics. These results establish all-vdW heterostructures as a highly attractive platform for integrated coherent light sources in layered-material photonic architectures and scalable quantum-photonic circuits.
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Submitted 23 July, 2026;
originally announced July 2026.
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Probing Interface-Driven Mechanisms of Non-Classical Light in van der Waals Heterostructures
Authors:
Bárbara L. T. Rosa,
Lara Greten,
Raphaela de Oliveira,
César Ribahi,
Aris Koulas-Simos,
Chirag C. Palekar,
Yara Gobato,
Ingrid D. Barcelos,
Andreas Knorr,
Stephan Reitzenstein
Abstract:
Single-photon emitters in two-dimensional semiconductors offer a versatile platform for integrated quantum photonics, yet their performance is strongly influenced by local dielectric environments and substrate-induced disorder. Here, we examine SPEs in monolayer WSe$_2$ incorporated into hBN/WSe$_2$/Clinochlore van der Waals heterostructures and assess how interface-mediated dielectric modulation…
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Single-photon emitters in two-dimensional semiconductors offer a versatile platform for integrated quantum photonics, yet their performance is strongly influenced by local dielectric environments and substrate-induced disorder. Here, we examine SPEs in monolayer WSe$_2$ incorporated into hBN/WSe$_2$/Clinochlore van der Waals heterostructures and assess how interface-mediated dielectric modulation governs their optical and quantum characteristics. Low-temperature micro-photoluminescence reveals narrow emission lines (100 - 300 $μ$eV) and robust non-classical behavior, with $g^{(2)}(0) = 0.13 \pm 0.02$ on SiO$_2$ and $0.54 \pm 0.02$ for emitters directly coupled to Clinochlore. Magneto-optical measurements yield effective g-factors near -8, consistent with defect states hybridized with dark excitons. WSe$_2$ on Clinochlore exhibits up to a fivefold enhancement in emission intensity, attributed to coupling with Fe-related substrate states that introduce resonant absorption near 1.75 eV. Kelvin probe force microscopy confirms strong dielectric contrast across thin and thick Clinochlore regions. Time-resolved photoluminescence shows that emitters on SiO$_2$ display a single $\approx 4$ ns lifetime, whereas those on Clinochlore exhibit biexponential dynamics with sub-nanosecond and tens-of-nanoseconds decay components. A phenomenological model incorporating coupling to bright and dark Fe-related states in Clinochlore accounts for modified excitation pathways. These results establish interface dielectric engineering in vdW heterostructures as an effective strategy for tailoring the radiative dynamics and brightness of quantum emitters in atomically thin materials.
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Submitted 3 March, 2026;
originally announced March 2026.
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Interplay of energy and charge transfer in WSe2/CrSBr heterostructures
Authors:
José Roberto de Toledo,
Caique Serati de Brito,
Barbara L. T. Rosa,
Alisson R. Cadore,
César Ricardo Rabahi,
Paulo E. Faria Junior,
Ana Carolina Ferreira de Brito,
Talieh S. Ghiasi,
Josep Ingla-Aynés,
Christian Schüller,
Herre S. J. van der Zant,
Stephan Reitzenstein,
Ingrid D. Barcelos,
Florian Dirnberger,
Yara Galvão Gobato
Abstract:
Van der Waals heterostructures (vdWHs) composed of transition-metal dichalcogenides (TMDs) and layered magnetic semiconductors offer great opportunities to manipulate exciton and valley properties of TMDs. Here, we present magneto-photoluminescence (PL) studies in a WSe2 monolayer (ML) on a CrSBr crystal, an anisotropic layered antiferromagnetic semiconductor. Our results reveal unique behavior of…
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Van der Waals heterostructures (vdWHs) composed of transition-metal dichalcogenides (TMDs) and layered magnetic semiconductors offer great opportunities to manipulate exciton and valley properties of TMDs. Here, we present magneto-photoluminescence (PL) studies in a WSe2 monolayer (ML) on a CrSBr crystal, an anisotropic layered antiferromagnetic semiconductor. Our results reveal unique behavior of each of the ML-WSe2 PL peaks under magnetic field that is distinct from the pristine case. An intriguing feature is the clear enhancement of the PL intensity that we observe each time the external magnetic field tunes the energy of an exciton in CrSBr into resonance with one of the optical states of WSe2. This result suggests a magnetic field-controlled resonant energy transfer (RET) beyond other effects reported in similar structures. Our work provides deep insight on the importance of different mechanisms into magnetic vdWHs and underscores its great potential for light harvesting and emission enhancement of two-dimensional materials.
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Submitted 31 August, 2025;
originally announced September 2025.
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Ultrafast transition from coherent to incoherent polariton nonlinearities in a hybrid 1L-WS2/plasmon structure
Authors:
Daniel Timmer,
Moritz Gittinger,
Thomas Quenzel,
Alisson R. Cadore,
Barbara L. T. Rosa,
Wenshan Li,
Giancarlo Soavi,
Daniel C. Lünemann,
Sven Stephan,
Lara Greten,
Marten Richter,
Andreas Knorr,
Antonietta De Sio,
Martin Silies,
Giulio Cerullo,
Andrea C. Ferrari,
Christoph Lienau
Abstract:
Exciton polaritons based on atomically thin semiconductors are essential building blocks of quantum optoelectronic devices. Their properties are governed by an ultrafast and oscillatory energy transfer between their excitonic and photonic constituents, resulting in the formation of polaritonic quasiparticles with pronounced nonlinearities induced by the excitonic component. In metallic nanoresonat…
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Exciton polaritons based on atomically thin semiconductors are essential building blocks of quantum optoelectronic devices. Their properties are governed by an ultrafast and oscillatory energy transfer between their excitonic and photonic constituents, resulting in the formation of polaritonic quasiparticles with pronounced nonlinearities induced by the excitonic component. In metallic nanoresonators, dissipation phenomena limit the polariton lifetime to a few ten femtoseconds, so short that the role of these polaritons for the nonlinearities of such hybrids is yet unexplored. Here, we use ultrafast two-dimensional electronic spectroscopy (2DES) to uncover coherent polariton dynamics in a hybrid monolayer (1L) WS2/plasmonic nanostructure. With respect to an uncoupled WS2 flake, we observe an over 20-fold, polarization-dependent enhancement of the optical nonlinearity and a rapid evolution of the 2DES spectra within ~70 fs. We relate these dynamics to a transition from coherent polaritons to incoherent excitations, unravel the microscopic optical nonlinearities, and show the potential of coherent polaritons for ultrafast all-optical switching.
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Submitted 28 July, 2025;
originally announced July 2025.
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Probing Noncentrosymmetric 2D Materials by Fourier Space Second Harmonic Imaging
Authors:
Lucas Lafeta,
Sean Hartmann,
Bárbara Rosa,
Stephan Reitzenstein,
Leandro M. Malard,
Achim Hartschuh
Abstract:
The controlled assembly of twisted 2D structures requires precise determination of the crystal orientation of their component layers. In the established procedure, the second-harmonic generation (SHG) intensity of a noncentrosymmetric layer is recorded while rotating the polarization of both the incident laser field and detected SHG, which can be time-consuming and tedious. Here, we demonstrate th…
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The controlled assembly of twisted 2D structures requires precise determination of the crystal orientation of their component layers. In the established procedure, the second-harmonic generation (SHG) intensity of a noncentrosymmetric layer is recorded while rotating the polarization of both the incident laser field and detected SHG, which can be time-consuming and tedious. Here, we demonstrate that the crystal orientation of transition metal dichalcogenides and hexagonal boron nitride can be directly determined by recording SHG images generated by tightly focused laser beams in Fourier space. Using an azimuthally polarized laser beam, the SHG image distinctly reflects the hexagonal structure of the crystal lattice, revealing its orientation quickly and accurately. This technique could significantly impact the field of twistronics, which studies the effects of the relative angle between the layers of a stacked 2D structure, as well as advances the nanofabrication of 2D materials.
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Submitted 3 September, 2024;
originally announced September 2024.
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Electrical manipulation of intervalley trions in twisted MoSe$_2$ homobilayers at room temperature
Authors:
Bárbara L. T. Rosa,
Paulo E. Faria Junior,
Alisson R. Cadore,
Yuhui Yang,
Aris Koulas-Simos,
Chirag C. Palekar,
Sefaattin Tongay,
Jaroslav Fabian,
Stephan Reitzenstein
Abstract:
The impressive physics and applications of intra- and interlayer excitons in a transition metal dichalcogenide twisted-bilayer make these systems compelling platforms for exploring the manipulation of their optoelectronic properties through electrical fields. This work studies the electrical control of excitonic complexes in twisted MoSe$_2$ homobilayer devices at room temperature. Gate-dependent…
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The impressive physics and applications of intra- and interlayer excitons in a transition metal dichalcogenide twisted-bilayer make these systems compelling platforms for exploring the manipulation of their optoelectronic properties through electrical fields. This work studies the electrical control of excitonic complexes in twisted MoSe$_2$ homobilayer devices at room temperature. Gate-dependent micro-photoluminescence spectroscopy reveals an energy tunability of several meVs originating from the emission of excitonic complexes. Furthermore, our study investigates the twist-angle dependence of valley properties by fabricating devices with stacking angles of $θ\sim1\degree$, $θ\sim4\degree$ and $θ\sim18\degree$. Strengthened by density functional theory calculations, the results suggest that, depending on the twist angle, the conduction band minima and hybridized states at the \textbf{Q}-point promote the formation of intervalley hybrid trions involving the \textbf{Q}-and \textbf{K}-points in the conduction band and the \textbf{K}-point in the valence band. By revealing the gate control of exciton species in twisted homobilayers, our findings open new avenues for engineering multifunctional optoelectronic devices based on ultrathin semiconducting systems.
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Submitted 11 October, 2024; v1 submitted 10 July, 2024;
originally announced July 2024.
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Nature of long-lived moiré interlayer excitons in electrically tunable MoS$_{2}$/MoSe$_{2}$ heterobilayers
Authors:
Evgeny M. Alexeev,
Carola M. Purser,
Carmem M. Gilardoni,
James Kerfoot,
Hao Chen,
Alisson R. Cadore,
Bárbara L. T. Rosa,
Matthew S. G. Feuer,
Evans Javary,
Patrick Hays,
Kenji Watanabe,
Takashi Taniguchi,
Seth Ariel Tongay,
Dhiren M. Kara,
Mete Atatüre,
Andrea C. Ferrari
Abstract:
Interlayer excitons in transition-metal dichalcogenide heterobilayers combine high binding energy and valley-contrasting physics with long optical lifetime and strong dipolar character. Their permanent electric dipole enables electric-field control of emission energy, lifetime, and location. Device material and geometry impacts the nature of the interlayer excitons via their real- and momentum-spa…
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Interlayer excitons in transition-metal dichalcogenide heterobilayers combine high binding energy and valley-contrasting physics with long optical lifetime and strong dipolar character. Their permanent electric dipole enables electric-field control of emission energy, lifetime, and location. Device material and geometry impacts the nature of the interlayer excitons via their real- and momentum-space configurations. Here, we show that interlayer excitons in MoS$_{2}$/MoSe$_{2}$ heterobilayers are formed by charge carriers residing at the Brillouin zone edges, with negligible interlayer hybridization. We find that the moiré superlattice leads to the reversal of the valley-dependent optical selection rules, yielding a positively valued g-factor and cross-polarized photoluminescence. Time-resolved photoluminescence measurements reveal that the interlayer exciton population retains the optically induced valley polarization throughout its microsecond-long lifetime. The combination of long optical lifetime and valley polarization retention makes MoS$_{2}$/MoSe$_{2}$ heterobilayers a promising platform for studying fundamental bosonic interactions and developing excitonic circuits for optical information processing.
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Submitted 4 June, 2024;
originally announced June 2024.
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Enhancement of interlayer exciton emission in a TMDC heterostructure via a multi-resonant chirped microresonator up to room temperature
Authors:
Chirag C. Palekar,
Barbara Rosa,
Niels Heermeier,
Ching-Wen Shih,
Imad Limame,
Aris Koulas-Simos,
Arash Rahimi-Iman,
Stephan Reitzenstein
Abstract:
We report on multi-resonance chirped distributed Bragg reflector (DBR) microcavities. These systems are employed to investigate the light-mater interaction with both intra- and inter-layer excitons of transition metal dichalcogenide (TMDC) bilayer heterostructures. The chirped DBRs consisting of SiO2 and Si3N4 layers with gradually changing thickness exhibit a broad stopband with a width exceeding…
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We report on multi-resonance chirped distributed Bragg reflector (DBR) microcavities. These systems are employed to investigate the light-mater interaction with both intra- and inter-layer excitons of transition metal dichalcogenide (TMDC) bilayer heterostructures. The chirped DBRs consisting of SiO2 and Si3N4 layers with gradually changing thickness exhibit a broad stopband with a width exceeding 600 nm. Importantly, and in contrast to conventional single-resonance microcavities, our structures provide multiple resonances across a broad spectral range, which can be matched to spectrally distinct resonances of the embedded TMDC heterostructures. We study cavity-coupled emission of both intra- and inter-layer excitons from an integrated WSe2/MoSe2 heterostructure in a chirped microcavity system. We observe an enhanced interlayer exciton emission with a Purcell factor of 6.67 +- 1.02 at 4 K. Additionally, we take advantage of cavity-enhanced emission of the interlayer exciton to investigate its temperature-dependent luminescence lifetime, which yields a value of 60 ps at room temperature. Our approach provides an intriguing platform for future studies of energetically distant and confined excitons in different semiconducting materials, which paves the way for various applications such as microlasers and single-photon sources by enabling precise control and manipulation of excitonic interactions utilizing multimode resonance light-matter interaction.
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Submitted 9 March, 2024;
originally announced March 2024.
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FRET$-$Calc: A Free Software and Web Server for Förster Resonance Energy Transfer Calculation
Authors:
Leandro Benatto,
Omar Mesquita,
João L. B. Rosa,
Lucimara S. Roman,
Marlus Koehler,
Rodrigo B. Capaz,
Graziâni Candiotto
Abstract:
Förster Resonance Energy Transfer Calculator (FRET$-$Calc) is a program and web server that analyzes molar extinction coefficient of the acceptor, emission spectrum of the donor, and the refractive index spectrum of the donor/acceptor blend. Its main function is to obtain important parameters of the FRET process from experimental data, such as: (i) effective refractive index, (ii) overlap integral…
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Förster Resonance Energy Transfer Calculator (FRET$-$Calc) is a program and web server that analyzes molar extinction coefficient of the acceptor, emission spectrum of the donor, and the refractive index spectrum of the donor/acceptor blend. Its main function is to obtain important parameters of the FRET process from experimental data, such as: (i) effective refractive index, (ii) overlap integral, (iii) Förster radius, (iii) FRET efficiency and (iv) FRET rate. FRET$-$Calc is license free software that can be run via dedicated web server (nanocalc.org) or downloading the program executables (for Unix, Windows, and macOS) from the FRET$-$Calc repository on GitHub. The program features a user$-$friendly interface, making it suitable for materials research and teaching purposes. In addition, the program is optimized to run on normal computers and is lightweight. An example will be given with the step by step of its use and results obtained.
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Submitted 26 November, 2023;
originally announced November 2023.
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Amplification of interlayer exciton emission in twisted WSe$_2$/WSe$_2$/MoSe$_2$ heterotrilayers
Authors:
Chirag C. Palekar,
Paulo E. Faria Junior,
Barbara Rosa,
Frederico B. Sousa,
Leandro M. Malard,
Jaroslav Fabian,
Stephan Reitzenstein
Abstract:
Transition metal dichalcogenide (TMDC) heterostructures have unique properties that depend on the twisting angle and stacking order of two or more monolayers. However, their practical applications are limited by the low photoluminescence yield of interlayer excitons. This limits the use of layered 2D materials as a versatile platform for developing innovative optoelectronic and spintronic devices.…
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Transition metal dichalcogenide (TMDC) heterostructures have unique properties that depend on the twisting angle and stacking order of two or more monolayers. However, their practical applications are limited by the low photoluminescence yield of interlayer excitons. This limits the use of layered 2D materials as a versatile platform for developing innovative optoelectronic and spintronic devices. In this study, we report on the emission enhancement of interlayer excitons in multilayered-stacked monolayers through the fabrication of heterotrilayers consisting of WSe$_2$/WSe$_2$/MoSe$_2$ with differing twist angles. Our results show that an additional WSe$_2$ monolayer introduces new absorption pathways, leading to an improvement in the emission of interlayer excitons by more than an order of magnitude. The emission boost is affected by the twist angle, and we observe a tenfold increase in the heterotrilayer area when there is a 44$^\circ$ angle between the WSe$_2$ and MoSe$_2$ materials, as opposed to their heterobilayer counterparts. Furthermore, using density functional theory, we identify the emergence of new carrier transfer pathways in the three-layer sample which extends the current understanding of 2D semiconducting heterostructures. In addition, our research provides a viable way to significantly enhance the emission of interlayer excitons. The emission enhancement of interlayer excitons is significant not only for studying the fundamental properties of interlayer excitons, but also for enabling optoelectronic applications that utilize engineered 2D quantum materials with high luminescence yield.
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Submitted 4 November, 2023;
originally announced November 2023.
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Twist Angle Dependence of Exciton Resonances in WSe$_2$/MoSe$_2$ Moiré Heterostructures
Authors:
Chirag Chandrakant Palekar,
Joakim Hagel,
Barbara Rosa,
Samuel Brem,
Ching-Wen Shih,
Imad Limame,
Martin von Helversen,
Sefaattin Tongay,
Ermin Malic,
Stephan Reitzenstein
Abstract:
Van der Waals heterostructures based on TMDC semiconducting materials have emerged as promising materials due to their spin-valley properties efficiently contrived by the stacking-twist angle. The twist angle drastically alters the interlayer excitonic response by determining the spatial modulation, confining moiré potential, and atomic reconstruction in those systems. Nonetheless, the impact of t…
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Van der Waals heterostructures based on TMDC semiconducting materials have emerged as promising materials due to their spin-valley properties efficiently contrived by the stacking-twist angle. The twist angle drastically alters the interlayer excitonic response by determining the spatial modulation, confining moiré potential, and atomic reconstruction in those systems. Nonetheless, the impact of the interlayer twist angle on the band alignment of the monolayers composing the heterostructure has received scant attention in the current research. Here, we systematically investigate the twist-angle dependence of intra- and inter-layer excitons in twisted WSe2/MoSe2 heterobilayers. By performing photoluminescence excitation spectroscopy, we identify the twist-angle dependence of interlayer emission response, where an energy redshift of about 100 meV was observed for increasing twist angles. The applied microscopic theory predicts, on the contrary, a blueshift, which suggests that additional features, such as atomic reconstruction, may also surpass the moiré potential confinement. Those findings also prompt the effects of dielectric screening by addressing the redshift response to the stacking layer order. Furthermore, our findings support the evidence of a band offset dependence on the twist angle for the adjacent monolayers composing the heterobilayer system. Our fundamental study of exciton resonances deepens the current understanding of the physics of twisted TMDC heterostructures and paves the way for future experiments and theoretical works.
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Submitted 28 September, 2023;
originally announced September 2023.
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In-situ spontaneous emission control of MoSe$_2$-WSe$_2$ interlayer excitons with near-unity quantum yield
Authors:
Bo Han,
Chirag Chandrakant Palekar,
Sven Stephan,
Frederik Lohof,
Victor Nikolaevich Mitryakhin,
Jens-Christian Drawer,
Alexander Steinhoff,
Lukas Lackner,
Martin Silies,
Bárbara Rosa,
Martin Esmann,
Falk Eilenberger,
Christopher Gies,
Stephan Reitzenstein,
Christian Schneider
Abstract:
Optical resonators are a powerful platform to control the spontaneous emission dynamics of excitons in solid-state nanostructures. Here, we study a MoSe$_2$-WSe$_2$ van-der-Waals heterostructure that is integrated in a widely tunable open optical microcavity to gain insights into fundamental optical properties of the emergent interlayer charge-transfer excitons. First, we utilize an ultra-low qual…
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Optical resonators are a powerful platform to control the spontaneous emission dynamics of excitons in solid-state nanostructures. Here, we study a MoSe$_2$-WSe$_2$ van-der-Waals heterostructure that is integrated in a widely tunable open optical microcavity to gain insights into fundamental optical properties of the emergent interlayer charge-transfer excitons. First, we utilize an ultra-low quality factor open planar vertical cavity and investigate the modification of the excitonic lifetime as on- and off-resonant conditions are met with consecutive longitudinal modes. Time-resolved photoluminescence measurements reveal that the interlayer exciton lifetime can thus be periodically tuned with an amplitude of 110 ps. The resulting oscillations of the interlayer exciton lifetime allows us to extract a 0.5 ns free-space radiative lifetime and a quantum efficiency as high as 81 \%. We subsequently engineer the local density of optical states by introducing a spatially confined and fully spectrally tunable Tamm-plasmon resonance. The dramatic redistribution of the local optical modes in this setting allows us to encounter a profound inhibition of spontaneous emission of the interlayer excitons by a factor of 3.2. We expect that specifically engineering the inhibition of radiation from moiré excitons is a powerful tool to steer their thermalization, and eventually their condensation into coherent condensate phases.
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Submitted 20 December, 2023; v1 submitted 26 June, 2023;
originally announced June 2023.
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Monolayer WS$_2$ electro- and photo-luminescence enhancement by TFSI treatment
Authors:
A. R. Cadore,
B. L. T. Rosa,
I. Paradisanos,
S. Mignuzzi,
D. De Fazio,
E. M. Alexeev,
J. E. Muench,
G. Kakavelakis,
S. M. Shinde,
D. Yoon,
S. Tongay,
K. Watanabe,
T. Taniguchi,
E. Lidorikis,
I. Goykhman,
G. Soavi,
A. C. Ferrari
Abstract:
Layered material heterostructures (LMHs) can be used to fabricate electroluminescent devices operating in the visible spectral region. A major advantage of LMH-light emitting diodes (LEDs) is that electroluminescence (EL) emission can be tuned across that of different exciton complexes (e.g. biexcitons, trions, quintons) by controlling the charge density. However, these devices have an EL quantum…
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Layered material heterostructures (LMHs) can be used to fabricate electroluminescent devices operating in the visible spectral region. A major advantage of LMH-light emitting diodes (LEDs) is that electroluminescence (EL) emission can be tuned across that of different exciton complexes (e.g. biexcitons, trions, quintons) by controlling the charge density. However, these devices have an EL quantum efficiency as low as$\sim$10$^{-4}$\%. Here, we show that the superacid bis-(triuoromethane)sulfonimide (TFSI) treatment of monolayer WS$_2$-LEDs boosts EL quantum efficiency by over one order of magnitude at room temperature. Non-treated devices emit light mainly from negatively charged excitons, while the emission in treated ones predominantly involves radiative recombination of neutral excitons. This paves the way to tunable and efficient LMH-LEDs
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Submitted 2 May, 2023;
originally announced May 2023.
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Identification of exciton complexes in a charge-tuneable Janus WSeS monolayer
Authors:
Matthew S. G. Feuer,
Alejandro R. -P. Montblanch,
Mohammed Sayyad,
Carola M. Purser,
Ying Qin,
Evgeny M. Alexeev,
Alisson R. Cadore,
Barbara L. T. Rosa,
James Kerfoot,
Elaheh Mostaani,
Radosław Kalęba,
Pranvera Kolari,
Jan Kopaczek,
Kenji Watanabe,
Takashi Taniguchi,
Andrea C. Ferrari,
Dhiren M. Kara,
Sefaattin Tongay,
Mete Atatüre
Abstract:
Janus transition-metal dichalcogenide monolayers are fully artificial materials, where one plane of chalcogen atoms is replaced by chalcogen atoms of a different type. Theory predicts an in-built out-of-plane electric field, giving rise to long-lived, dipolar excitons, while preserving direct-bandgap optical transitions in a uniform potential landscape. Previous Janus studies had broad photolumine…
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Janus transition-metal dichalcogenide monolayers are fully artificial materials, where one plane of chalcogen atoms is replaced by chalcogen atoms of a different type. Theory predicts an in-built out-of-plane electric field, giving rise to long-lived, dipolar excitons, while preserving direct-bandgap optical transitions in a uniform potential landscape. Previous Janus studies had broad photoluminescence (>15 meV) spectra obfuscating their excitonic origin. Here, we identify the neutral, and negatively charged inter- and intravalley exciton transitions in Janus WSeS monolayer with $\sim 6$ meV optical linewidth. We combine a recently developed synthesis technique, with the integration of Janus monolayers into vertical heterostructures, allowing doping control. Further, magneto-optic measurements indicate that monolayer WSeS has a direct bandgap at the K points. This work provides the foundation for applications such as nanoscale sensing, which relies on resolving excitonic energy shifts, and photo-voltaic energy harvesting, which requires efficient creation of long-lived excitons and integration into vertical heterostructures.
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Submitted 13 October, 2022;
originally announced October 2022.
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Tunable out-of-plane excitons in 2D single crystal perovskites
Authors:
A. Fieramosca,
L. De Marco,
M. Passoni,
L. Polimeno,
A. Rizzo,
B. L. T. Rosa,
G. Cruciani,
L. Dominici,
M. De Giorgi,
G. Gigli,
L. C. Andreani,
D. Gerace,
D. Ballarini,
D. Sanvitto
Abstract:
Hybrid organic-inorganic perovskites have emerged as very promising materials for photonic applications, thanks to the great synthetic versatility that allows to tune their optical properties. In the two-dimensional (2D) crystalline form, these materials behave as multiple quantum-well heterostructures with stable excitonic resonances up to room temperature. In this work strong light-matter coupli…
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Hybrid organic-inorganic perovskites have emerged as very promising materials for photonic applications, thanks to the great synthetic versatility that allows to tune their optical properties. In the two-dimensional (2D) crystalline form, these materials behave as multiple quantum-well heterostructures with stable excitonic resonances up to room temperature. In this work strong light-matter coupling in 2D perovskite single-crystal flakes is observed, and the polarization-dependent exciton-polariton response is used to disclose new excitonic features. For the first time, an out-of-plane component of the excitons is observed, unexpected for such 2D systems and completely absent in other layered materials, such as transition-metal dichalcogenides. By comparing different hybrid perovskites with the same inorganic layer but different organic interlayers, it is shown how the nature of the organic ligands controllably affects the out-of-plane exciton-photon coupling. Such vertical dipole coupling is particularly sought in those systems, e.g. plasmonic nanocavities, in which the direction of the field is usually orthogonal to the material sheet. Organic interlayers are shown to affect also the strong birefringence associated to the layered structure, which is exploited in this work to completely rotate the linear polarization degree in only few microns of propagation, akin to what happens in metamaterials.
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Submitted 2 November, 2018;
originally announced November 2018.