Terahertz emission from transient currents and coherent phonons in layered MoSe$_2$ and WSe$_2$. (arXiv:2305.18805v1 [cond-mat.mtrl-sci])

2023-05-31T02:30:04+00:00May 31st, 2023|Categories: Publications|Tags: , |

Terahertz (THz) time-domain emission spectroscopy was performed on layered 2H-MoSe2 and 2H-WSe2. The THz emission shows an initial cycle attributed to surge currents and is followed by oscillations attributed to coherent interlayer phonon modes. To obtain the frequencies of the interlayer vibrations, analysis of the THz emission waveforms were performed, separating the two contributions to the total waveform. Results of the fitting show several vibrational modes in the range of 5.87 to 32.75 cm-1 for the samples, attributed to infrared-active interlayer shear and breathing modes. This study demonstrates that THz emission spectroscopy provides a means of observing these low frequency vibrational modes in layered materials.

Published in: "arXiv Material Science".

Programmable Nanowrinkle-Induced Room-Temperature Exciton Localization in Monolayer WSe2. (arXiv:2305.15506v1 [cond-mat.mes-hall])

2023-05-28T08:32:15+00:00May 28th, 2023|Categories: Publications|Tags: , |

Localized states in two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been the subject of intense study, driven by potential applications in quantum information science. Despite the rapidly growing knowledge surrounding these emitters, their microscopic nature is still not fully understood, limiting their production and application. Motivated by this challenge, and by recent theoretical and experimental evidence showing that nanowrinkles generate localized room-temperature emitters, we demonstrate a method to intentionally induce wrinkles with collections of stressors, showing that long-range wrinkle direction and position are controllable with patterned array design. Nano-photoluminescence (nano-PL) imaging combined with detailed strain modeling based on measured wrinkle topography establishes a correlation between wrinkle properties, particularly shear strain, and localized exciton emission. Beyond the array-induced super-wrinkles, nano-PL spatial maps further reveal that the strain environment around individual stressors is heterogeneous due to the presence of fine wrinkles that are less deterministic. Detailed nanoscale hyperspectral images uncover a wide range of low-energy emission peaks originating from these fine wrinkles, and show that the states can be tightly confined to regions < 10 nm, even in ambient conditions. These results establish a promising potential route towards realizing room temperature quantum emission in 2D TMDC systems.

Published : "arXiv Mesoscale and Nanoscale Physics".

Programmable Nanowrinkle-Induced Room-Temperature Exciton Localization in Monolayer WSe2. (arXiv:2305.15506v1 [cond-mat.mes-hall])

2023-05-28T08:32:14+00:00May 28th, 2023|Categories: Publications|Tags: , |

Localized states in two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been the subject of intense study, driven by potential applications in quantum information science. Despite the rapidly growing knowledge surrounding these emitters, their microscopic nature is still not fully understood, limiting their production and application. Motivated by this challenge, and by recent theoretical and experimental evidence showing that nanowrinkles generate localized room-temperature emitters, we demonstrate a method to intentionally induce wrinkles with collections of stressors, showing that long-range wrinkle direction and position are controllable with patterned array design. Nano-photoluminescence (nano-PL) imaging combined with detailed strain modeling based on measured wrinkle topography establishes a correlation between wrinkle properties, particularly shear strain, and localized exciton emission. Beyond the array-induced super-wrinkles, nano-PL spatial maps further reveal that the strain environment around individual stressors is heterogeneous due to the presence of fine wrinkles that are less deterministic. Detailed nanoscale hyperspectral images uncover a wide range of low-energy emission peaks originating from these fine wrinkles, and show that the states can be tightly confined to regions < 10 nm, even in ambient conditions. These results establish a promising potential route towards realizing room temperature quantum emission in 2D TMDC systems.

Published : "arXiv Mesoscale and Nanoscale Physics".

Resolidified Chalcogen Precursors for High‐Quality 2D Semiconductor Growth

2023-04-11T10:21:19+00:00April 11th, 2023|Categories: Publications|Tags: , , , |

Two-dimensional (2D) semiconductors including transition metal dichalcogenides (TMDCs) have gained attention in optoelectronics for their extraordinary properties. However, the large amount and locally distributed lattice defects affect the optical properties of 2D TMDCs, and the defects originate from unstable factors in the synthesis process. In this work, we develop a method of pre-melting and resolidification of chalcogen precursors (sulfur and selenium), namely resolidified chalcogen, as precursor for the chemical vapor deposition growth of TMDCs with ultrahigh quality and uniformity. Taking WS2 as an example, the monolayer WS2 shows uniform fluorescence intensity and a small full-width at half-maximum of photoluminescence peak at low temperatures with an average value of 13.6 ± 1.9 meV. The defect densities at the interior and edge region are both low and comparable, i.e., (9 ± 3) × 1012 cm-2 and (10 ± 4) × 1012 cm-2, indicating its high structural quality and uniformity. This method is universal in growing high quality monolayer MoS2, WSe2, MoSe2, and will benefit their applications.

Published in: "Angewandte Chemie International Edition".

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers. (arXiv:2303.12881v1 [cond-mat.mes-hall])

2023-03-24T04:30:37+00:00March 24th, 2023|Categories: Publications|Tags: , |

The spin Hall effect (SHE), in which electrical current generates transverse spin current, plays an important role in spintronics for the generation and manipulation of spin-polarized electrons. The phenomenon originates from spin-orbit coupling. In general, stronger spin-orbit coupling favors larger SHEs but shorter spin relaxation times and diffusion lengths. To achieve both large SHEs and long-range spin transport in a single material has remained a challenge. Here we demonstrate a giant intrinsic SHE in AB-stacked MoTe2/WSe2 moir’e bilayers by direct magneto optical imaging. Under moderate electrical currents with density < 1 A/m, we observe spin accumulation on transverse sample edges that nearly saturates the spin density. We also demonstrate long-range spin Hall transport and efficient non-local spin accumulation limited only by the device size (about 10 um). The gate dependence shows that the giant SHE occurs only near the Chern insulating state, and at low temperatures, it emerges after the quantum anomalous Hall breakdown. Our results demonstrate moir'e engineering of Berry curvature and large SHEs for potential spintronics applications.

Published : "arXiv Mesoscale and Nanoscale Physics".

Observation of Rydberg moir’e excitons. (arXiv:2303.09844v1 [cond-mat.mes-hall])

2023-03-20T04:30:51+00:00March 20th, 2023|Categories: Publications|Tags: , , |

Rydberg excitons, the solid-state counterparts of Rydberg atoms, have sparked considerable interest in harnessing their quantum application potentials, whereas a major challenge is realizing their spatial confinement and manipulation. Lately, the rise of two-dimensional moir’e superlattices with highly tunable periodic potentials provides a possible pathway. Here, we experimentally demonstrate this capability through the observation of Rydberg moir’e excitons (XRM), which are moir’e trapped Rydberg excitons in monolayer semiconductor WSe2 adjacent to twisted bilayer graphene. In the strong coupling regime, the XRM manifest as multiple energy splittings, pronounced redshift, and narrowed linewidth in the reflectance spectra, highlighting their charge-transfer character where electron-hole separation is enforced by the strongly asymmetric interlayer Coulomb interactions. Our findings pave the way for pursuing novel physics and quantum technology exploitation based on the excitonic Rydberg states.

Published : "arXiv Mesoscale and Nanoscale Physics".

Dynamically tunable moir’e Rydberg excitons in a monolayer semiconductor on twisted bilayer graphene. (arXiv:2303.08980v1 [cond-mat.mes-hall])

2023-03-17T02:29:30+00:00March 17th, 2023|Categories: Publications|Tags: , , |

Moir’e excitons are emergent optical excitations in 2D semiconductors with deep moir’e superlattice potentials. While these excitations have been realized in several platforms, a system with dynamically tunable moir’e potential to tailor the moir’e exciton properties is yet to be realized. Here, we present a continuously tunable moir’e potential in a monolayer WSe2 that is enabled by its proximity to twisted bilayer graphene (TBG) near the magic-angle. Due to its flat electronic bands, charge distribution is highly localized and forms a triangular lattice in TBG. Tuning the local charge density via electrostatic gating, TBG thus provides a spatially varying and dynamically tunable dielectric superlattice for modulating monolayer exciton wavefunctions. By performing optical reflection spectroscopy, we observe emergent moir’e exciton Rydberg branches in monolayer WSe2 with increased energy splitting upon doping TBG. The twist-angle dependence reveals that the observation is due to a hybridization between bright and dark Rydberg states enabled by the moir’e potential. Further, at the magic-angle near 1.1{deg}, the moir’e Rydberg excitons form a sawtooth pattern with doping owing to the formation of strongly correlated states in the TBG. Our study provides a new platform for engineering moir’e excitons as well as optical accessibility to the electronic states with small correlation gaps in TBG.

Published in: "arXiv Material Science".

Epitaxial van der Waals heterostructures of Cr2Te3 on 2D materials. (arXiv:2303.03076v1 [cond-mat.mtrl-sci])

2023-03-07T02:29:47+00:00March 7th, 2023|Categories: Publications|Tags: , , |

Achieving large-scale growth of two-dimensional (2D) ferromagnetic materials with high Curie temperature (TC) and perpendicular magnetic anisotropy (PMA) is highly desirable for the development of ultra-compact magnetic sensors and magnetic memories. In this context, van der Waals (vdW) Cr2Te3 appears as a promising candidate. Bulk Cr2Te3 exhibits strong PMA and a TC of 180 K. Moreover, both PMA and TC might be adjusted in ultrathin films by engineering composition, strain, or applying an electric field. In this work, we demonstrate the molecular beam epitaxy (MBE) growth of vdW heterostructures of five-monolayer quasi-freestanding Cr2Te3 on three classes of 2D materials: graphene (semimetal), WSe2 (semiconductor) and Bi2Te3 (topological insulator). By combining structural and chemical analysis down to the atomic level with ab initio calculations, we confirm the single crystalline character of Cr2Te3 films on the 2D materials with sharp vdW interfaces. They all exhibit PMA and TC close to the bulk Cr2Te3 value of 180 K. Ab initio calculations confirm this PMA and show how its strength depends on strain. Finally, Hall measurements reveal a strong anomalous Hall effect, which changes sign at a given temperature. We theoretically explain this effect by a sign change of the Berry phase close to the Fermi level. This transition temperature depends on the 2D material in proximity, notably as a consequence of charge transfer. MBE-grown Cr2Te3/2D material bilayers constitute model systems for the further development of spintronic devices combining PMA, large spin-orbit coupling and sharp vdW interface.

Published in: "arXiv Material Science".

Interlayer donor-acceptor pair excitons in MoSe2/WSe2 moir’e heterobilayer. (arXiv:2302.13003v1 [cond-mat.mes-hall])

2023-02-28T04:30:26+00:00February 28th, 2023|Categories: Publications|Tags: , , , |

Localized interlayer excitons (LIXs) in two-dimensional moir’e superlattices exhibit sharp and dense emission peaks, making them promising as highly tunable single-photon sources. However, the fundamental nature of these LIXs is still elusive. Here, we show the donor-acceptor pair (DAP) mechanism as one of the origins of these excitonic peaks. Numerical simulation results of the DAP model agree with the experimental photoluminescence spectra of LIX in the moir’e MoSe2/WSe2 heterobilayer. In particular, we find that the emission energy-lifetime correlation and the nonmonotonic power dependence of the lifetime agree well with the DAP IX model. Our results provide insight into the physical mechanism of LIX formation in moir’e heterostructures and pave new directions for engineering interlayer exciton properties in moir’e superlattices.

Published : "arXiv Mesoscale and Nanoscale Physics".

Tunable phononic coupling in excitonic quantum emitters. (arXiv:2302.13484v1 [cond-mat.mes-hall])

2023-02-28T04:30:21+00:00February 28th, 2023|Categories: Publications|Tags: , |

Engineering the coupling between fundamental quantum excitations is at the heart of quantum science and technologies. A significant case is the creation of quantum light sources in which coupling between single photons and phonons can be controlled and harnessed to enable quantum information transduction. Here, we report the deterministic creation of quantum emitters featuring highly tunable coupling between excitons and phonons. The quantum emitters are formed in strain-induced quantum dots created in homobilayer semiconductor WSe2. The colocalization of quantum confined interlayer excitons and THz interlayer breathing mode phonons, which directly modulate the exciton energy, leads to a uniquely strong phonon coupling to single-photon emission. The single-photon spectrum of interlayer exciton emission features a single-photon purity >83% and multiple phonon replicas, each heralding the creation of a phonon Fock state in the quantum emitter. Owing to the vertical dipole moment of the interlayer exciton, the phonon-photon interaction is electrically tunable in a wide range, promising to reach the strong coupling regime. Our result demonstrates a new type of solid-state quantum excitonic-optomechanical system at the atomic interface that emits flying photonic qubits coupled with stationary phonons, which could be exploited for quantum transduction and interconnection.

Published : "arXiv Mesoscale and Nanoscale Physics".

Topology hierarchy of transition metal dichalcogenides built from quantum spin Hall layers. (arXiv:2302.13662v1 [cond-mat.mtrl-sci])

2023-02-28T02:29:37+00:00February 28th, 2023|Categories: Publications|Tags: , , , , |

The evolution of the physical properties of two-dimensional material from monolayer limit to the bulk reveals unique consequences from dimension confinement and provides a distinct tuning knob for applications. Monolayer 1T’-phase transition metal dichalcogenides (1T’-TMDs) with ubiquitous quantum spin Hall (QSH) states are ideal two-dimensional building blocks of various three-dimensional topological phases. However, the stacking geometry was previously limited to the bulk 1T’-WTe2 type. Here, we introduce the novel 2M-TMDs consisting of translationally stacked 1T’-monolayers as promising material platforms with tunable inverted bandgaps and interlayer coupling. By performing advanced polarization-dependent angle-resolved photoemission spectroscopy as well as first-principles calculations on the electronic structure of 2M-TMDs, we revealed a topology hierarchy: 2M-WSe2, MoS2, and MoSe2 are weak topological insulators (WTIs), whereas 2M-WS2 is a strong topological insulator (STI). Further demonstration of topological phase transitions by tunning interlayer distance indicates that band inversion amplitude and interlayer coupling jointly determine different topological states in 2M-TMDs. We propose that 2M-TMDs are parent compounds of various exotic phases including topological superconductors and promise great application potentials in quantum electronics due to their flexibility in patterning with two-dimensional materials.

Published in: "arXiv Material Science".

In-Plane Electric Field Induced Orbital Hybridization of Excitonic States In Monolayer WSe2. (arXiv:2302.11373v1 [cond-mat.mes-hall])

2023-02-23T04:30:18+00:00February 23rd, 2023|Categories: Publications|Tags: , |

The giant exciton binding energy and the richness of degrees of freedom make monolayer transition metal dichalcogenide an unprecedented playground for exploring exciton physics in 2D systems. Thanks to the well energetically separated excitonic states, the response of the discrete excitonic states to the electric field could be precisely examined. Here we utilize the photocurrent spectroscopy to probe excitonic states under a static in-plane electric field. We demonstrate that the in-plane electric field leads to a significant orbital hybridization of Rydberg excitonic states with different angular momentum (especially orbital hybridization of 2s and 2p) and consequently optically actives 2p-state exciton. Besides, the electric-field controlled mixing of the high lying exciton state and continuum band enhances the oscillator strength of the discrete excited exciton states. This electric field modulation of the excitonic states in monolayer TMDs provides a paradigm of the manipulation of 2D excitons for potential applications of the electro-optical modulation in 2D semiconductors.

Published : "arXiv Mesoscale and Nanoscale Physics".

Dark exciton energy splitting in monolayer WSe2: insights from time-dependent density-functional theory. (arXiv:2302.08375v1 [cond-mat.mtrl-sci])

2023-02-17T02:29:45+00:00February 17th, 2023|Categories: Publications|Tags: , |

We present here a formalism based on time-dependent density-functional theory (TDDFT) to describe characteristics of both intra- and inter-valley excitons in semiconductors, the latter of which had remained a challenge. Through the usage of an appropriate exchange-correlation kernel (nanoquanta), we trace the energy difference between the intra- and inter-valley dark excitons in monolayer (1L) WSe2 to the domination of the exchange part in the exchange-correlation energies of these states. Furthermore, our calculated transition contribution maps establish the momentum resolved weights of the electron-hole excitations in both bright and dark excitons thereby providing a comprehensive understanding of excitonic properties of 1L WSe2. We find that the states consist of hybridized excitations around the corresponding valleys which leads to brightening of the dark excitons, i.e., significantly decreasing their lifetime which is reflected in the PL spectrum. Using many-body perturbation theory, we calculate the phonon contribution to the energy bandgap and the linewidths of the excited electrons, holes and (bright) exciton to find that as the temperature increases the bandgap significantly decreases, while the linewidths increase. Our work paves for describing the ultrafast charge dynamics of transition metal dichalcogenide within an ab initio framework.

Published in: "arXiv Material Science".

Ultra-bright single photon source based on an atomically thin material. (arXiv:2302.06340v1 [quant-ph])

2023-02-14T04:30:30+00:00February 14th, 2023|Categories: Publications|Tags: |

Solid-state single photon sources are central building blocks in quantum communication networks and on-chip quantum information processing. Atomically thin crystals were established as possible candidates to emit non-classical states of light, however, the performance of monolayer-based single photon sources has so far been lacking behind state-of-the-art devices based on volume crystals. Here, we implement a single photon source based on an atomically thin sheet of WSe2 coupled to a spectrally tunable optical cavity. It is characterized by a high single photon purity with a $g^{(2)}(0)$ value as low as $4.7 pm 0.7 %$ and a record-high first lens brightness of linearly polarized photons as large as $65 pm 4 %$. Interestingly, the high performance of our devices allows us to observe genuine quantum interference phenomena in a Hong-Ou-Mandel experiment. Our results demonstrate that open cavities and two-dimensional materials constitute an excellent platform for ultra-bright quantum light sources: the unique properties of such two-dimensional materials and the versatility of open cavities open an inspiring avenue for novel quantum optoelectronic devices.

Published : "arXiv Mesoscale and Nanoscale Physics".

Van der Waals device integration beyond the limits of van der Waals forces via adhesive matrix transfer. (arXiv:2302.05989v1 [physics.app-ph])

2023-02-14T02:29:40+00:00February 14th, 2023|Categories: Publications|Tags: , , , |

Pristine van der Waals (vdW) interfaces between two-dimensional (2D) and other materials are core to emerging optical and electronic devices. Their direct fabrication is, however, challenged as the vdW forces are weak and cannot be tuned to accommodate integration of arbitrary layers without solvents, sacrificial-layers or high-temperatures, steps that can introduce damage. To address these limitations, we introduce a single-step 2D material-to-device integration approach in which forces promoting transfer are decoupled from the vdW forces at the interface of interest. We use this adhesive matrix transfer to demonstrate conventionally-forbidden direct integration of diverse 2D materials (MoS2, WSe2, PtS2, GaS) with dielectrics (SiO2, Al2O3), and scalable, aligned heterostructure formation, both foundational to device development. We then demonstrate a single-step integration of monolayer-MoS2 into arrays of transistors. With no exposure to polymers or solvents, clean interfaces and pristine surfaces are preserved, which can be further engineered to demonstrate both n- and p-type behavior. Beyond serving as a platform to probe the intrinsic properties of sensitive nanomaterials without the influence of processing steps, our technique allows efficient formation of unconventional device form-factors, with an example of flexible transistors demonstrated.

Published in: "arXiv Material Science".

Anisotropic Lattice Expansion of Monolayer WSe2 Revealed by Ultrafast Electron Diffraction. (arXiv:2302.02554v1 [cond-mat.mtrl-sci])

2023-02-07T02:29:34+00:00February 7th, 2023|Categories: Publications|Tags: |

Bulk layered MX2 transition metal chalcogenides (M = Mo, W and X = S, Se) are known to exhibit an indirect to direct band gap transition as the number of layers is reduced. Previous time-resolved work has principally focused on the investigation of the transient evolution of the band structure after photo-excitation, but additional information on the dynamics of the concomitant lattice rearrangement is needed to fully understand this phenomenon. Here, ultrafast electron diffraction is used to probe the atomic motion and bond dilation in monolayer WSe2 with femtosecond temporal resolution. The change in the intensity of the Bragg diffraction spots is characterized by single-exponential dynamics, consistent with a collective response of the lattice during electron-phonon and phonon-phonon equilibration that is repeatable over many hours of illumination with ultrafast pulses. Moreover, a transient and highly anisotropic lattice expansion is observed. A possible explanation for this behavior is axial strain induced by the laser excitation that breaks the degeneracy of the in-plane phonon modes, and that strongly influences the electronic band structure. Such degeneracy-breaking induced by distortions in the lattice are well characterized in static strain measurements, and the results presented here provide valuable insights into the nature and time scales of the structural rearrangement that occurs following optical photo-excitation in monolayer tungsten diselenide.

Published in: "arXiv Material Science".

A room-temperature moir’e interlayer exciton laser. (arXiv:2302.01266v1 [physics.optics])

2023-02-03T04:30:21+00:00February 3rd, 2023|Categories: Publications|Tags: , , , , |

Moir’e superlattices in van der Waals heterostructures offer highly tunable quantum systems with emergent electronic and excitonic properties such as superconductivity, topological edge states, and moir’e-trapped excitons. Theoretical calculations predicted the existence of the moir’e potential at elevated temperatures; however, its impact on the optical properties of interlayer excitons (IXs) at room temperature is lacking, and the benefits of the moir’e effects for lasing applications remain unexplored. We report that the moir’e potential in a molybdenum disulfide/tungsten diselenide (MoS2/WSe2) heterobilayer system can significantly enhance light emission, elongate the IX lifetime, and modulate the IX emission energy at room temperature. By integrating a moir’e superlattice with a silicon topological nanocavity, we achieve ultra-low-threshold lasing at the technologically important telecommunication O-band thanks to the significant moir’e modulation. Moreover, the high-quality topological nanocavities facilitate the highest spectral coherence of < 0.1 nm linewidth among all reported two-dimensional material-based laser systems. Our findings not only open a new avenue for studying correlated states at elevated temperatures, but also enable novel architectures for integrated on-chip photonics and optoelectronics.

Published : "arXiv Mesoscale and Nanoscale Physics".

Electroluminescence as a probe of strong exciton-plasmon coupling in few-layer WSe2. (arXiv:2302.00023v1 [cond-mat.mes-hall])

2023-02-02T04:30:21+00:00February 2nd, 2023|Categories: Publications|Tags: |

The manipulation of coupled quantum excitations is of fundamental importance in realizing novel photonic and optoelectronic devices. We use electroluminescence to probe plasmon-exciton coupling in hybrid structures each consisting of a nanoscale plasmonic tunnel junction and few-layer two-dimensional transition-metal dichalcogenide transferred onto the junction. The resulting hybrid states act as a novel dielectric environment to affect the radiative recombination of hot carriers in the plasmonic nanostructure. We determine the plexcitonic spectrum from the electroluminescence and find Rabi splittings exceeding 25 meV, near the onset of strong coupling. Our experimental findings are supported by electromagnetic simulations that enable us to explore systematically, and in detail, the emergence of plexciton polaritons as well as the polarization characteristics of their far-field emission. Electroluminescence modulated by plexciton coupling provides potential applications for engineering compact photonic devices with tunable optical and electrical properties.

Published : "arXiv Mesoscale and Nanoscale Physics".

Dynamics of moire trion and its valley polarization in microfabricated WSe2/MoSe2 heterobilayer. (arXiv:2301.11012v1 [physics.optics])

2023-01-27T02:29:55+00:00January 27th, 2023|Categories: Publications|Tags: , , |

The moire potential, induced by stacking two monolayer semiconductors with slightly different lattice mismatches, acts as periodic quantum confinement for optically generated excitons, resulting in spatially ordered zero-dimensional quantum systems. However, there are limitations to exploring intrinsic optical properties of moire excitons due to ensemble averaged and broadened emissions from many peaks caused by the inhomogeneity of the moire potential. In this study, we proposed a microfabrication technique based on focused Ga+ ion beams, which enables us to control the number of peaks originating from the moire potential and thus explore unknown moire optical characteristics of WSe2/MoSe2 heterobilayers. By taking advantage of this approach, we reveal emissions from a single moire exciton and charged moire exciton (trion) under electrostatic doping conditions. We show the momentum dark moire trion state above the bright trion state with a splitting energy of approximately 4 meV and clarify that the dynamics are determined by the initial trion population in the bright state. Furthermore, the degree of negative circularly polarized emissions and their valley dynamics of moire trions are dominated by a very long valley relaxation process lasting ~700 ns. Our findings on microfabricated heterobilayers could be viewed as an extension of our groundbreaking efforts in the field of quantum optics application using moire superlattices.

Published in: "arXiv Material Science".

Strain-induced dynamic control over the population of quantum emitters in two-dimensional materials. (arXiv:2301.10273v1 [cond-mat.mtrl-sci])

2023-01-26T02:29:16+00:00January 26th, 2023|Categories: Publications|Tags: , |

The discovery of quantum emitters in two-dimensional materials has triggered a surge of research to assess their suitability for quantum photonics. While their microscopic origin is still the subject of intense studies, ordered arrays of quantum emitters are routinely fabricated using static strain-gradients, which are used to drive excitons toward localized regions of the 2D crystals where quantum-light-emission takes place. However, the possibility of using strain in a dynamic fashion to control the appearance of individual quantum emitters has never been explored so far. In this work, we tackle this challenge by introducing a novel hybrid semiconductor-piezoelectric device in which WSe2 monolayers are integrated onto piezoelectric pillars delivering both static and dynamic strains. Static strains are first used to induce the formation of quantum emitters, whose emission shows photon anti-bunching. Their excitonic population and emission energy are then reversibly controlled via the application of a voltage to the piezoelectric pillar. Numerical simulations combined with drift-diffusion equations show that these effects are due to a strain-induced modification of the confining-potential landscape, which in turn leads to a net redistribution of excitons among the different quantum emitters. Our work provides relevant insights into the role of strain in the formation of quantum emitters in 2D materials and suggests a method to switch them on and off on demand.

Published in: "arXiv Material Science".

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