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The Structure and Dispersion of Exciton-Trion-Polaritons in Two-Dimensional Semiconductors. (arXiv:2101.02070v1 [cond-mat.mes-hall])

2021-01-07T04:30:37+00:00January 7th, 2021|Categories: Publications|Tags: , |

Coupling of excitons and photons in optical waveguides and cavities to realize polaritons has provided insights into light-matter interactions from the classical to the quantum regimes, generated new opportunities for engineering optical nonlinearities, and enabled novel technologies. Polaritons have also opened up new pathways to explore highly correlated many-body states of matter. In doped two-dimensional semiconductors, excitons and trions are not independent excitations but are strongly coupled as a result of Coulomb interactions. When excitons in such a material are also strongly coupled with light inside an optical waveguide, the resulting polariton states are coherent superpositions of exciton, trion, and photon states. We realize these exciton-trion-polaritons by coupling an electron-doped monolayer of two-dimensional material MoSe2 to the optical mode in a photonic crystal waveguide. The optical and Coulomb couplings among the excitons, trions, and photons result in three polariton bands. Our theoretical model, based on a many-body description of these polaritons, reproduces the measured polariton energy band dispersions and the energy splittings among the polariton bands with good accuracy. Our work not only sheds light on the nature of highly correlated many body exciton and trion states in doped semiconductors, but is also expected to open up new avenues for device technologies and for realizing optical nonlinearities

Published : "arXiv Mesoscale and Nanoscale Physics".

Exciton-phonon coupling strength in single-layer MoSe2 at room temperature. (arXiv:2012.11492v1 [cond-mat.mes-hall])

2020-12-22T02:29:40+00:00December 22nd, 2020|Categories: Publications|Tags: |

Single-layer transition metal dichalcogenides are at the center of an ever increasing research effort both in terms of fundamental physics and applications. Exciton-phonon coupling plays a key role in determining the (opto)electronic properties of these materials. However, the exciton-phonon coupling strength has not been measured at room temperature. Here, we develop two-dimensional micro-spectroscopy to determine exciton-phonon coupling of single-layer MoSe2. We detect beating signals as a function of waiting time T, induced by the coupling between the A exciton and the A’1 optical phonon. Analysis of two-dimensional beating maps combined with simulations provides the exciton-phonon coupling. The Huang-Rhys factor of ~1 is larger than in most other inorganic semiconductor nanostructures. Our technique offers a unique tool to measure exciton-phonon coupling also in other heterogeneous semiconducting systems with a spatial resolution ~260 nm, and will provide design-relevant parameters for the development of optoelectronic devices.

Published in: "arXiv Material Science".

Dipolariton propagation in a van der Waals TMDC with {Psi}-shaped channel guides and buffered channel branches. (arXiv:2012.08608v1 [cond-mat.mtrl-sci])

2020-12-17T02:30:06+00:00December 17th, 2020|Categories: Publications|Tags: , , |

Using a computational approach based on the driven diffusion equation for dipolariton wave packets, we simulate the diffusive dynamics of dipolaritons in an optical microcavity embedded with a transition-metal dichalcogenide (TMDC) heterogeneous bilayer encompassing a {Psi}-shaped channel. By considering exciton-dipolaritons, which are a three way superposition of direct excitons, indirect excitons and cavity photons, we are able to drive the dipolaritons in our system by the use of an electric voltage and investigate their diffusive properties. More precisely, we study the propagation of dipolaritons present in a MoSe2-WS2 heterostructure, where the dipolariton propagation is guided by a {Psi}-shaped channel. We also consider the propagation of dipolaritons in the presence of a buffer in the {Psi}-shaped channel and study resulting changes in efficiency. By our consideration of a geometrically novel dipolariton channel guide, we introduce novel designs for optical routers at room temperature as well as replicate the dipolariton redistribution efficiencies of previously proposed polaritronic applications.

Published in: "arXiv Material Science".

Optical nonlinearities in the excited carrier density of atomically thin transition metal dichalcogenides. (arXiv:2012.07642v1 [cond-mat.mes-hall])

2020-12-15T04:30:49+00:00December 15th, 2020|Categories: Publications|Tags: , , , |

In atomically thin semiconductors based on transition metal dichalcogenides, photoexcitation can be used to generate high densities of electron-hole pairs. Due to optical nonlinearities, which originate from Pauli blocking and many-body effects of the excited carriers, the generated carrier density will deviate from a linear increase in pump fluence. In this paper, we use a theoretical approach that combines results from ab-initio electronic-state calculations with a many-body treatment of optical excitation to describe nonlinear absorption properties and the resulting excited carrier dynamics. We determine the validity range of a linear approximation for the excited carrier density vs. pump power and identify the role and magnitude of optical nonlinearities at elevated excitation carrier densities for MoS2, MoSe2, WS2, and WSe2 considering various excitation conditions. We find that for above-band-gap photoexcitation, the use of a linear absorption coefficient of the unexcited system can strongly underestimate the achievable carrier density for a wide range of pump fluences due to many-body renormalizations of the two-particle density-of-states.

Published : "arXiv Mesoscale and Nanoscale Physics".

Universal superlattice potential for 2D materials from twisted interface inside h-BN substrate. (arXiv:2011.03933v1 [cond-mat.mes-hall])

2020-11-10T04:30:27+00:00November 10th, 2020|Categories: Publications|Tags: , , , |

Lateral superlattices in 2D materials are emerging as a powerful platform for exploring novel quantum phenomena, which can be realized through the proximity coupling in forming moir’e pattern with another layer. This approach, however, is invasive, material-specific, and requires small lattice mismatch and suitable band alignment, largely limited to graphene and transition metal dichalcogenides (TMDs). Hexagonal boron nitride (h-BN) of anti-parallel (AA’) stacking order has been an indispensable building block, as dielectric substrates and capping layers for realizing high quality van der Waals devices. There is also emerging interest on parallelly aligned h-BN of Bernal (AB) stacking, where the broken inversion and mirror symmetries lead to out-of-plane electrical polarization with sign controlled by interlayer translation. Here we show that the laterally patterned electrical polarization at a nearly parallel interface within the h-BN substrate or capping layer can be exploited to create non-invasively a universal superlattice potential in general 2D materials. The feasibility is demonstrated by first principle calculations for monolayer MoSe2, black phosphorus, and antiferromagnetic MnPSe3 on such h-BN substrate. The potential strength can reach 200 meV, customizable in this range through choice of vertical distance of target material from the interface in h-BN. We also find sizable out-of-plane electric field at the h-BN surface, which can realize superlattice potential for interlayer excitons in TMD bilayers as well as dipolar molecules. The idea is further generalized to AB stacked h-BN film subject to torsion with adjacent layers all twisted with an angle, which allows the potential and field strength to

Published : "arXiv Mesoscale and Nanoscale Physics".

On the Elastic Properties and Fracture Patterns of MoX2 (X = S, Se, Te) Membranes: A Reactive Molecular Dynamics Study. (arXiv:2010.11976v1 [cond-mat.mtrl-sci])

2020-10-26T02:29:36+00:00October 26th, 2020|Categories: Publications|Tags: |

We carried out fully-atomistic reactive molecular dynamics simulations to study the elastic properties and fracture patterns of transition metal dichalcogenide (TMD) MoX2 (X=S, Se, Te) membranes, in their 2H and 1T phases, within the framework of the Stillinger-Weber potential. Results showed that the fracture mechanism of these membranes occurs through a fast crack propagation followed by their abrupt rupture into moieties. As a general trend, the translated arrangement of the chalcogen atoms in the 1T phase contributes to diminishing their structural stability when contrasted with the 2H one. Among the TMDs studied here, 2H-MoSe2 has a higher tensile strength (25.98 GPa).

Published in: "arXiv Material Science".

Valley Depolarization in Monolayer Transition-Metal Dichalcogenides with Zone-Corner Acoustic Phonons. (arXiv:2010.11758v1 [cond-mat.mes-hall])

2020-10-23T04:30:21+00:00October 23rd, 2020|Categories: Publications|Tags: , , |

Although single-layer transition-metal dichalcogenides with novel valley functionalities are promising candidate to realize valleytronic devices, the essential understanding of valley depolarization mechanisms is still incomplete. Based on pump-probe experiments performed for MoSe2 and WSe2 monolayers and corroborating analysis from density functional calculations, we demonstrate that coherent phonons at the K-point of the Brillouin zone can effectively mediate the valley transfer of electron carriers. In the MoSe2 monolayer case, we identify this mode as the flexural acoustic ZA(K) mode, which has broken inversion symmetry and thus can enable electron spin-flip during valley transfer. On the other hand, in the monolayer WSe2 case where spin-preserving inter-valley relaxations are preferred coherent LA(K) phonons with even inversion symmetry are efficiently generated. These findings establish that, while the specifics of inter-valley relaxations depend on the spin alignments of energy bands, the K-point phonons should be taken into account as an effective valley depolarization pathway in transition metal dichalcogenide monolayers.

Published : "arXiv Mesoscale and Nanoscale Physics".

Epitaxial single-crystal growth of transition metal dichalcogenide monolayers via atomic sawtooth Au surface. (arXiv:2010.10097v1 [cond-mat.mtrl-sci])

2020-10-21T02:30:00+00:00October 21st, 2020|Categories: Publications|Tags: , , , , , , |

Growth of two-dimensional van der Waals layered single-crystal (SC) films is highly desired to manifest intrinsic material sciences and unprecedented devices for industrial applications. While wafer-scale SC hexagonal boron nitride film has been successfully grown, an ideal growth platform for diatomic transition metal dichalcogenide (TMdC) film has not been established to date. Here, we report the SC growth of TMdC monolayers in a centimeter scale via atomic sawtooth gold surface as a universal growth template. Atomic tooth-gullet surface is constructed by the one-step solidification of liquid gold, evidenced by transmission-electron-microscopy. Anisotropic adsorption energy of TMdC cluster, confirmed by density-functional calculations, prevails at the periodic atomic-step edge to yield unidirectional epitaxial growth of triangular TMdC grains, eventually forming the SC film, regardless of Miller indices. Growth using atomic sawtooth gold surface as a universal growth template is demonstrated for several TMdC monolayer films, including WS2, WSe2, MoS2, MoSe2/WSe2 heterostructure, and W1-xMoxS2 alloy. Our strategy provides a general avenue for the SC growth of diatomic van der Waals heterostructures in a wafer scale, to further facilitate the applications of TMdCs in post silicon technology.

Published in: "arXiv Material Science".

Mechanical properties of lateral transition metal dichalcogenide heterostructures. (arXiv:2009.13031v1 [cond-mat.mtrl-sci])

2020-09-29T02:29:48+00:00September 29th, 2020|Categories: Publications|Tags: , , , , |

Transition metal dichalcogenide (TMD) monolayers attract great attention due to their specific structural, electronic and mechanical properties. The formation of their lateral heterostructures allows a new degree of flexibility in engineering electronic and optoelectronic devices. However, the mechanical properties of the lateral heterostructures are rarely investigated. In this study, a comparative investigation on the mechanical characteristics of 1H, 1T’ and 1H/1T’ heterostructure phases of different TMD monolayers including molybdenum disulfide (MoS2) molybdenum diselenide (MoSe2), Tungsten disulfide (WS2), and Tungsten diselenide (WSe2) was conducted by means of density functional theory (DFT) calculations. Our results indicate that the lateral heterostructures have a relatively weak mechanical strength for all the TMD monolayers. The significant correlation between the mechanical properties of the TMD monolayers and their structural phases can be used to tune their stiffness of the materials. Our findings, therefore, suggest a novel strategy to manipulate the mechanical characteristics of TMDs by engineering their structural phases for their practical applications.

Published in: "arXiv Material Science".

Bosonic condensation of exciton-polaritons in an atomically thin crystal. (arXiv:2009.11885v1 [cond-mat.mes-hall])

2020-09-28T02:29:16+00:00September 28th, 2020|Categories: Publications|Tags: |

The emergence of two-dimensional crystals has revolutionized modern solid-state physics. From a fundamental point of view, the enhancement of charge carrier correlations has sparked enormous research activities in the transport- and quantum optics communities. One of the most intriguing effects, in this regard, is the bosonic condensation and spontaneous coherence of many-particle complexes. Here, we find compelling evidence of bosonic condensation of exciton-polaritons emerging from an atomically thin crystal of MoSe2 embedded in a dielectric microcavity under optical pumping. The formation of the condensate manifests itself in a sudden increase of luminescence intensity in a threshold-like manner, and a significant spin-polarizability in an externally applied magnetic field. Spatial coherence is mapped out via highly resolved real-space interferometry, revealing a spatially extended condensate. Our device represents a decisive step towards the implementation of coherent light-sources based on atomically thin crystals, as well as non-linear, valleytronic coherent devices.

Published in: "arXiv Material Science".

Experimental observation of topological exciton-polaritons in transition metal dichalcogenide monolayers. (arXiv:2009.11237v1 [cond-mat.mes-hall])

2020-09-24T02:29:28+00:00September 24th, 2020|Categories: Publications|Tags: |

The rise of quantum science and technologies motivates photonics research to seek new platforms with strong light-matter interactions to facilitate quantum behaviors at moderate light intensities. One promising platform to reach such strong light-matter interacting regimes is offered by polaritonic metasurfaces, which represent ultrathin artificial media structured on nano-scale and designed to support polaritons – half-light half-matter quasiparticles. Topological polaritons, or ‘topolaritons’, offer an ideal platform in this context, with unique properties stemming from topological phases of light strongly coupled with matter. Here we explore polaritonic metasurfaces based on 2D transition metal dichalcogenides (TMDs) supporting in-plane polarized exciton resonances as a promising platform for topological polaritonics. We enable a spin-Hall topolaritonic phase by strongly coupling valley polarized in-plane excitons in a TMD monolayer with a suitably engineered all-dielectric topological photonic metasurface. We first show that the strong coupling between topological photonic bands supported by the metasurface and excitonic bands in MoSe2 yields an effective phase winding and transition to a topolaritonic spin-Hall state. We then experimentally realize this phenomenon and confirm the presence of one-way spin-polarized edge topolaritons. Combined with the valley polarization in a MoSe2 monolayer, the proposed system enables a new approach to engage the photonic angular momentum and valley degree of freedom in TMDs, offering a promising platform for photonic/solid-state interfaces for valleytronics and spintronics.

Published in: "arXiv Material Science".

High-Performance Flexible Nanoscale Field-Effect Transistors Based on Transition Metal Dichalcogenides. (arXiv:2009.04056v1 [cond-mat.mtrl-sci])

2020-09-10T02:29:34+00:00September 10th, 2020|Categories: Publications|Tags: , , , |

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) are good candidates for high-performance flexible electronics. However, most demonstrations of such flexible field-effect transistors (FETs) to date have been on the micron scale, not benefitting from the short-channel advantages of 2D-TMDs. Here, we demonstrate flexible monolayer MoS2 FETs with the shortest channels reported to date (down to 50 nm) and remarkably high on-current (up to 470 {mu}A/{mu}m at 1 V drain-to-source voltage) which is comparable to flexible graphene or crystalline silicon FETs. This is achieved using a new transfer method wherein contacts are initially patterned on the rigid TMD growth substrate with nanoscale lithography, then coated with a polyimide (PI) film which becomes the flexible substrate after release, with the contacts and TMD. We also apply this transfer process to other TMDs,reporting the first flexible FETs with MoSe2 and record on-current for flexible WSe2 FETs. These achievements push 2D semiconductors closer to a technology for low-power and high-performance flexible electronics.

Published in: "arXiv Material Science".

Seeded growth of high-quality transition metal dichalcogenide single crystals via chemical vapor transport. (arXiv:2009.02988v1 [cond-mat.mtrl-sci])

2020-09-08T02:29:30+00:00September 8th, 2020|Categories: Publications|Tags: , , |

Transition metal dichalcogenides (TMDs) are van der Waals layered materials with sizable and tunable bandgaps, offering promising platforms for two-dimensional electronics and optoelectronics. To this end, the bottleneck is how to acquire high-quality single crystals in a facile and efficient manner. As one of the most widely employed method of single-crystal growth, conventional chemical vapor transport (CVT) generally encountered problems including the excess nucleation that leads to small crystal clusters and slow growth rate. To address these issues, a seed crystal is introduced to suppress the nucleation and an inner tube is adopted as both a separator and a flow restrictor, favoring the growth of large-size and high-quality TMD single crystals successfully. Three examples are presented, the effective growth of millimeter-sized MoSe2 and MoTe2 single crystals, and the greatly shortened growth period for PtSe2 single crystal, all of which are synthesized in high quality according to detailed characterizations. The mechanism of seeded CVT is discussed. Furthermore, a phototransistor based on exfoliated multi-layered MoSe2 displays excellent photoresponse in ambient conditions, and considerably rapid rise and fall time of 110 and 125 us are obtained. This work paves the way for developing a facile and versatile method to synthesize high-quality TMD single crystals in laboratory, which could serve as favorable functional materials for potential low-dimensional optoelectronics.

Published in: "arXiv Material Science".

Many-body effect in optical properties of monolayer molybdenum diselenide. (arXiv:2008.10801v1 [cond-mat.mes-hall])

2020-08-26T04:30:41+00:00August 26th, 2020|Categories: Publications|Tags: |

Excitons in monolayer transition metal dichalcogenide (TMD) provide a paradigm of composite Boson in 2D system. This letter reports a photoluminescence and reflectance study of excitons in monolayer molybdenum diselenide (MoSe2) with electrostatic gating. We observe the repulsive and attractive Fermi polaron modes of the band edge exciton, its excited state and the spin-off excitons. Our data validate the polaronic behavior of excitonic states in the system quantitatively where the simple three-particle trion model is insufficient to explain.

Published : "arXiv Mesoscale and Nanoscale Physics".

The role of device asymmetries and Schottky barriers on the helicity-dependent photoresponse of 2D phototransistors. (arXiv:2008.09023v1 [cond-mat.mtrl-sci])

2020-08-21T02:29:35+00:00August 21st, 2020|Categories: Publications|Tags: |

Circular photocurrents (CPC), namely circular photogalvanic (CPGE) and photon drag effects, have recently been reported both in monolayer and multilayer transition metal dichalcogenide (TMD) phototransistors. However, the underlying physics for the emergence of these effects are not yet fully understood. In particular, the emergence of CPGE is not compatible with the D3h crystal symmetry of two-dimensional TMDs, and should only be possible if the symmetry of the electronic states is reduced by influences such as an external electric field or mechanical strain. Schottky contacts, nearly ubiquitous in TMD-based transistors, can provide the high electric fields causing a symmetry breaking in the devices. Here, we investigate the effect of these Schottky contacts on the CPC by characterizing the helicity-dependent photoresponse of monolayer MoSe2 devices both with direct metal-MoSe2 Schottky contacts and with h-BN tunnel barriers at the contacts. We find that, when Schottky barriers are present in the device, additional contributions to CPC become allowed, resulting in emergence of CPC for illumination at normal incidence.

Published in: "arXiv Material Science".

Deep moir’e potentials in twisted transition metal dichalcogenide bilayers. (arXiv:2008.07696v1 [cond-mat.mes-hall])

2020-08-19T04:30:24+00:00August 19th, 2020|Categories: Publications|Tags: , |

In twisted bilayers of semiconducting transition metal dichalcogenides (TMDs), a combination of structural rippling and electronic coupling gives rise to periodic moir’e potentials that can confine charged and neutral excitations. Here, we report experimental measurements of the structure and spectroscopic properties of twisted bilayers of WSe2 and MoSe2 in the H-stacking configuration using scanning tunneling microscopy (STM). Our experiments reveal that the moir’e potential in these bilayers at small angles is unexpectedly large, reaching values of above 300 meV for the valence band and 150 meV for the conduction band – an order of magnitude larger than theoretical estimates based on interlayer coupling alone. We further demonstrate that the moir’e potential is a non-monotonic function of moir’e wavelength, reaching a maximum at around a 13nm moir’e period. This non-monotonicity coincides with a drastic change in the structure of the moir’e pattern from a continuous variation of stacking order at small moir’e wavelengths to a one-dimensional soliton dominated structure at large moir’e wavelengths. We show that the in-plane structure of the moir’e pattern is captured well by a continuous mechanical relaxation model, and find that the moir’e structure and internal strain rather than the interlayer coupling is the dominant factor in determining the moir’e potential. Our results demonstrate the potential of using precision moir’e structures to create deeply trapped carriers or excitations for quantum electronics and optoelectronics.

Published : "arXiv Mesoscale and Nanoscale Physics".

Unveiling the optical emission channels of monolayer semiconductors coupled to silicon nanoantennas. (arXiv:2007.12612v1 [cond-mat.mes-hall])

2020-07-27T04:30:15+00:00July 27th, 2020|Categories: Publications|Tags: , |

Monolayers (MLs) of transition metal dichalcogenides (TMDs) such as WSe2 and MoSe2 can be placed by dry stamping directly on broadband dielectric resonators, which have the ability to enhance the spontaneous emission rate and brightness of solid-state emitters at room temperature. We show strongly enhanced emission and directivity modifications in room temperature photoluminescence mapping experiments. By varying TMD material (WSe2 versus MoSe2) transferred on silicon nanoresonators with various designs (planarized versus non-planarized), we experimentally separate the different physical mechanisms that govern the global light emission enhancement. For WSe2 and MoSe2 we address the effects of Mie Resonances and strain in the monolayer. For WSe2 an important additional contribution comes from out-of-plane exciton dipoles. This paves the way for more targeted designs of TMD-Si nanoresonator structures for room temperature applications.

Published : "arXiv Mesoscale and Nanoscale Physics".

Novel 2D MoSe2 as a Promising Chemo-resistive Sensor for N2O Detection: A DFT Approach. (arXiv:2006.16698v1 [cond-mat.mtrl-sci])

2020-07-01T02:29:32+00:00July 1st, 2020|Categories: Publications|Tags: , |

We have investigated the structural and electronic properties of 2D MoSe2 monolayer using DFT approach. The adsorption energy of toxic N2O gas has been calculated at varying adsorbent distances from Top Mo (Top Se) configurations and observed that it increases as the N2O gas molecule moves towards the surface of 2D MoSe2 monolayer. In this work, as a result of N2O gas absorption, charge transfer and density of states (DOS) are changed and these parameters are extracted as electronic properties of 2D MoSe2 monolayer nano-gas sensor. The calculated results predict that there is increase in charge transfer with the decrease in adsorbent distance towards the monolayer. Meanwhile, the Fermi level shifts upward towards conduction band by -1.76 (-1.75) eV upon absorption of the N2O gas on the surface of 2D MoSe2 monolayer. Interestingly, the modification in DOS with N2O gas absorption redistribute and increase the density of electrons in the conduction band and thereby its conductivity. Moreover, the spin up and down states in the DOS results in considerable magnetic moment altering the magnetic property of the 2D MoSe2 monolayer. Later, the desorption property of the 2D MoSe2 monolayer towards the target N2O gas molecule at three different temperature are calculated. Thus, the paper concludes with outcomes of the structural and electronic properties aligning its behavior as a chemo-resistive nano-gas sensor and showing it as a potential applicant for sensing of toxic N2O gas molecule.

Published in: "arXiv Material Science".

Strain engineering in single-, bi- and tri-layer MoS2, MoSe2, WS2 and WSe2. (arXiv:2006.06660v1 [cond-mat.mtrl-sci])

2020-06-12T02:29:21+00:00June 12th, 2020|Categories: Publications|Tags: , , , |

Strain is a powerful tool to modify the optical properties of semiconducting transition metal dichalcogenides like MoS2, MoSe2, WS2 and WSe2. In this work we provide a thorough description of the technical details to perform uniaxial strain measurements on these two-dimensional semiconductors and we provide a straightforward calibration method to determine the amount of applied strain with high accuracy. We then employ reflectance spectroscopy to analyze the strain tunability of the electronic properties of single-, bi- and tri-layer MoS2, MoSe2, WS2 and WSe2. Finally, we quantify the flake-to-flake variability by analyzing 15 different single-layer MoS2 flakes.

Published in: "arXiv Material Science".

Enhanced exciton-exciton collisions in an ultra-flat monolayer MoSe2 prepared through deterministic flattening. (arXiv:2006.02640v1 [cond-mat.mes-hall])

2020-06-05T04:30:28+00:00June 5th, 2020|Categories: Publications|Tags: , , , |

Squeezing bubbles and impurities out of interlayer spaces by applying force through a few-layer graphene capping layer leads to van der Waals heterostructures with ultra-flat structure free from random electrostatic potential arising from charged impurities. Without the graphene capping layer, a squeezing process with an AFM tip induces applied-force-dependent charges of n ~ 2 x 10^12 cm^-2 uN^-1, resulting in strong intensity of trions in photoluminescence spectra of MoSe2 at low temperature. We found that a hBN/MoSe2/hBN prepared with the “modified nano-squeezing method” shows a strong excitonic emission with negligible trion peak, and the residual linewidth of the exciton peak is only 2.2 meV, which is comparable to the homogeneous limit. Furthermore, in this high-quality sample, we found that formation of biexciton occurs even at extremely low excitation power (Phi ~ 2.3 x 10^19 cm^-2 s^-1) due to the enhanced collisions between excitons.

Published : "arXiv Mesoscale and Nanoscale Physics".

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