Strong interaction between interlayer excitons and correlated electrons in WSe2/WS2 moiré superlattice

AbstractHeterobilayers of transition metal dichalcogenides (TMDCs) can form a moiré superlattice with flat minibands, which enables strong electron interaction and leads to various fascinating correlated states. These heterobilayers also host interlayer excitons in a type-II band alignment, in which optically excited electrons and holes reside on different layers but remain bound by the Coulomb interaction. Here we explore the unique setting of interlayer excitons interacting with strongly correlated electrons, and we show that the photoluminescence (PL) of interlayer excitons sensitively signals the onset of various correlated insulating states as the band filling is varied. When the system is in one of such states, the PL of interlayer excitons is relatively amplified at increased optical excitation power due to reduced mobility, and the valley polarization of interlayer excitons is enhanced. The moiré superlattice of the TMDC heterobilayer presents an exciting platform to engineer interlayer excitons through the periodic correlated electron states.

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Narrow-band high-lying excitons with negative-mass electrons in monolayer WSe2

Nature Communications ◽

10.1038/s41467-021-25499-2 ◽

2021 ◽

Vol 12 (1) ◽

Cited By ~ 1

Author(s):

Kai-Qiang Lin ◽

Chin Shen Ong ◽

Sebastian Bange ◽

Paulo E. Faria Junior ◽

Bo Peng ◽

...

Keyword(s):

Quantum Interference ◽

Second Harmonic ◽

Transition Metal Dichalcogenides ◽

Single Layer ◽

Optical Excitation ◽

Band Edge ◽

Negative Mass ◽

Strong Electron ◽

Interference Phenomenon ◽

Metal Dichalcogenides

AbstractMonolayer transition-metal dichalcogenides (TMDCs) show a wealth of exciton physics. Here, we report the existence of a new excitonic species, the high-lying exciton (HX), in single-layer WSe2 with an energy of ~3.4 eV, almost twice the band-edge A-exciton energy, with a linewidth as narrow as 5.8 meV. The HX is populated through momentum-selective optical excitation in the K-valleys and is identified in upconverted photoluminescence (UPL) in the UV spectral region. Strong electron-phonon coupling results in a cascaded phonon progression with equidistant peaks in the luminescence spectrum, resolvable to ninth order. Ab initio GW-BSE calculations with full electron-hole correlations explain HX formation and unmask the admixture of upper conduction-band states to this complex many-body excitation. These calculations suggest that the HX is comprised of electrons of negative mass. The coincidence of such high-lying excitonic species at around twice the energy of band-edge excitons rationalizes the excitonic quantum-interference phenomenon recently discovered in optical second-harmonic generation (SHG) and explains the efficient Auger-like annihilation of band-edge excitons.

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Structural phase transition and superconductivity hierarchy in 1T-TaS2 under pressure up to 100 GPa

npj Quantum Materials ◽

10.1038/s41535-021-00320-x ◽

2021 ◽

Vol 6 (1) ◽

Author(s):

Qing Dong ◽

Quanjun Li ◽

Shujia Li ◽

Xuhan Shi ◽

Shifeng Niu ◽

...

Keyword(s):

Structural Phase ◽

Transition Metal Dichalcogenides ◽

Phonon Coupling ◽

Structural Phase Transitions ◽

Strong Electron ◽

Electron Phonon Coupling ◽

Increasing Trend ◽

Metal Dichalcogenides ◽

Dome Shape ◽

Enhanced Superconductivity

AbstractThe adoption of high pressure not only reinforces the comprehension of the structure and exotic electronic states of transition metal dichalcogenides (TMDs) but also promotes the discovery of intriguing phenomena. Here, 1T-TaS2 was investigated up to 100 GPa, and re-enhanced superconductivity was found with structural phase transitions. The discovered I4/mmm TaS2 presents strong electron–phonon coupling, revealing a good superconductivity of the nonlayered structure. The P–T phase diagram shows a dome shape centered at ~20 GPa, which is attributed to the distortion of the 1T structure. Accompanied by the transition to nonlayered structure above 44.5 GPa, the superconducting critical temperature shows an increasing trend and reaches ~7 K at the highest studied pressure, presenting superior superconductivity compared to the original layered structure. It is unexpected that the pressure-induced re-enhanced superconductivity was observed in TMDs, and the transition from a superconductor with complicated electron-pairing mechanism to a phonon-mediated superconductor would expand the field of pressure-modified superconductivity.

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Investigation of Band Alignment for Hybrid 2D-MoS2/3D-β-Ga2O3 Heterojunctions with Nitridation

Nanoscale Research Letters ◽

10.1186/s11671-019-3181-x ◽

2019 ◽

Vol 14 (1) ◽

Cited By ~ 1

Author(s):

Ya-Wei Huan ◽

Ke Xu ◽

Wen-Jun Liu ◽

Hao Zhang ◽

Dmitriy Anatolyevich Golosov ◽

...

Keyword(s):

Valence Band ◽

Transition Metal Dichalcogenides ◽

Three Dimensional ◽

Optoelectronic Devices ◽

Band Alignment ◽

Band Offsets ◽

Group Iii ◽

Nanoelectronic Devices ◽

Metal Dichalcogenides ◽

Band Alignments

AbstractHybrid heterojunctions based on two-dimensional (2D) and conventional three-dimensional (3D) materials provide a promising way toward nanoelectronic devices with engineered features. In this work, we investigated the band alignment of a mixed-dimensional heterojunction composed of transferred MoS2 on β-Ga2O3($$ 2- $$2-01) with and without nitridation. The conduction and valence band offsets for unnitrided 2D-MoS2/3D-β-Ga2O3 heterojunction were determined to be respectively 0.43 ± 0.1 and 2.87 ± 0.1 eV. For the nitrided heterojunction, the conduction and valence band offsets were deduced to 0.68 ± 0.1 and 2.62 ± 0.1 eV, respectively. The modified band alignment could result from the dipole formed by charge transfer across the heterojunction interface. The effect of nitridation on the band alignments between group III oxides and transition metal dichalcogenides will supply feasible technical routes for designing their heterojunction-based electronic and optoelectronic devices.

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Nanoscale Characterization of WSe2for Opto-electronics Applications

MRS Advances ◽

10.1557/adv.2017.410 ◽

2017 ◽

Vol 2 (60) ◽

pp. 3715-3720 ◽

Cited By ~ 1

Author(s):

Nirmal Adhikari ◽

Avra Bandyopadhyay ◽

Anupama Kaul

Keyword(s):

Transition Metal Dichalcogenides ◽

Chemical Vapor ◽

Absorber Layer ◽

Band Alignment ◽

Transport Layer ◽

Electron Transport Layer ◽

Kelvin Probe ◽

Nanoscale Characterization ◽

Efficient Charge ◽

Metal Dichalcogenides

ABSTRACTTwo dimensional (2D) thin transition metal dichalcogenides are being widely investigated for optoelectronics applications. Here, we report on the interfacial study of WSe2with photo-absorber materials for efficient charge transport using Kelvin Probe Force Microscopy (KPFM) for solar cell applications. The WSe2in these experiments was synthesized using Chemical Vapor Deposition (CVD) with a WO3powder and Se pellets as the precursors, where the selenium was placed upstream in an Ar carrier gas within the furnace at a temperature zone of 260-270°C. For the interfacial analysis, nanoscale KPFM measurements show an average surface potential of 125 meV for the CVD synthesized WSe2flakes. KPFM measurements signify that a thin layer of WSe2can be used to suppress back recombination of carriers between the electron transport layer (ETL) and the absorber layer. A proper band alignment between ETL and absorber layer helps to increase the overall device performance, which we will elaborate upon in this work. Capacitance-voltage and capacitance-frequency measurements were measured to study the role of defects.

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Highly-efficient heterojunction solar cells based on two-dimensional tellurene and transition metal dichalcogenides

Journal of Materials Chemistry A ◽

10.1039/c9ta00280d ◽

2019 ◽

Vol 7 (13) ◽

pp. 7430-7436 ◽

Cited By ~ 22

Author(s):

Kai Wu ◽

Huanhuan Ma ◽

Yunzhi Gao ◽

Wei Hu ◽

Jinlong Yang

Keyword(s):

Solar Cells ◽

Transition Metal ◽

Charge Separation ◽

Transition Metal Dichalcogenides ◽

Band Alignment ◽

Type Ii ◽

Two Dimensional ◽

Heterojunction Solar Cells ◽

Highly Efficient ◽

Metal Dichalcogenides

Tellurene and TMDs show desirable type II band alignment for constructing highly-efficient heterojunction solar cells with strong charge separation and enhanced sunlight absorption.

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Erratum: “Band alignment of two-dimensional transition metal dichalcogenides: Application in tunnel field effect transistors” [Appl. Phys. Lett. 103, 053513 (2013)]

Applied Physics Letters ◽

10.1063/1.4932088 ◽

2015 ◽

Vol 107 (13) ◽

pp. 139904 ◽

Cited By ~ 21

Author(s):

Cheng Gong ◽

Hengji Zhang ◽

Weihua Wang ◽

Luigi Colombo ◽

Robert M. Wallace ◽

...

Keyword(s):

Transition Metal ◽

Field Effect ◽

Field Effect Transistors ◽

Transition Metal Dichalcogenides ◽

Band Alignment ◽

Two Dimensional ◽

Metal Dichalcogenides

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Atomic–layer–confined multiple quantum wells enabled by monolithic bandgap engineering of transition metal dichalcogenides

Science Advances ◽

10.1126/sciadv.abd7921 ◽

2021 ◽

Vol 7 (13) ◽

pp. eabd7921

Author(s):

Yoon Seok Kim ◽

Sojung Kang ◽

Jae-Pil So ◽

Jong Chan Kim ◽

Kangwon Kim ◽

...

Keyword(s):

Transition Metal ◽

Quantum Wells ◽

Building Block ◽

Transition Metal Dichalcogenides ◽

Atomic Layer ◽

Band Alignment ◽

Type I ◽

Bandgap Engineering ◽

Strong Light ◽

Metal Dichalcogenides

Quantum wells (QWs), enabling effective exciton confinement and strong light-matter interaction, form an essential building block for quantum optoelectronics. For two-dimensional (2D) semiconductors, however, constructing the QWs is still challenging because suitable materials and fabrication techniques are lacking for bandgap engineering and indirect bandgap transitions occur at the multilayer. Here, we demonstrate an unexplored approach to fabricate atomic–layer–confined multiple QWs (MQWs) via monolithic bandgap engineering of transition metal dichalcogenides and van der Waals stacking. The WOX/WSe2 hetero-bilayer formed by monolithic oxidation of the WSe2 bilayer exhibited the type I band alignment, facilitating as a building block for MQWs. A superlinear enhancement of photoluminescence with increasing the number of QWs was achieved. Furthermore, quantum-confined radiative recombination in MQWs was verified by a large exciton binding energy of 193 meV and a short exciton lifetime of 170 ps. This work paves the way toward monolithic integration of band-engineered heterostructures for 2D quantum optoelectronics.

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Interlayer exciton formation, relaxation, and transport in TMD van der Waals heterostructures

Light Science & Applications ◽

10.1038/s41377-021-00500-1 ◽

2021 ◽

Vol 10 (1) ◽

Author(s):

Ying Jiang ◽

Shula Chen ◽

Weihao Zheng ◽

Biyuan Zheng ◽

Anlian Pan

Keyword(s):

Integrated Circuits ◽

Integrated Circuit ◽

Van Der Waals ◽

Transition Metal Dichalcogenides ◽

Band Alignment ◽

Great Promise ◽

Comprehensive Overview ◽

Potential Applications ◽

Metal Dichalcogenides ◽

Population Recombination

AbstractVan der Waals (vdW) heterostructures based on transition metal dichalcogenides (TMDs) generally possess a type-II band alignment that facilitates the formation of interlayer excitons between constituent monolayers. Manipulation of the interlayer excitons in TMD vdW heterostructures holds great promise for the development of excitonic integrated circuits that serve as the counterpart of electronic integrated circuits, which allows the photons and excitons to transform into each other and thus bridges optical communication and signal processing at the integrated circuit. As a consequence, numerous studies have been carried out to obtain deep insight into the physical properties of interlayer excitons, including revealing their ultrafast formation, long population recombination lifetimes, and intriguing spin-valley dynamics. These outstanding properties ensure interlayer excitons with good transport characteristics, and may pave the way for their potential applications in efficient excitonic devices based on TMD vdW heterostructures. At present, a systematic and comprehensive overview of interlayer exciton formation, relaxation, transport, and potential applications is still lacking. In this review, we give a comprehensive description and discussion of these frontier topics for interlayer excitons in TMD vdW heterostructures to provide valuable guidance for researchers in this field.

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Probing biexciton in monolayer WS2 through controlled many-body interaction

2D Materials ◽

10.1088/2053-1583/ac3b1c ◽

2021 ◽

Author(s):

Suman Chatterjee ◽

Sarthak Das ◽

Garima Gupta ◽

Kenji Watanabe ◽

Takashi Taniguchi ◽

...

Keyword(s):

Radiative Recombination ◽

Transition Metal Dichalcogenides ◽

Excitation Power ◽

Equation Model ◽

Final States ◽

Many Body ◽

Time Resolved ◽

Spectral Separation ◽

Metal Dichalcogenides ◽

Time Resolved Photoluminescence

Abstract The monolayers of semiconducting transition metal dichalcogenides host strongly bound excitonic complexes and are an excellent platform for exploring many-body physics. Here we demonstrate a controlled kinetic manipulation of the five-particle excitonic complex, the charged biexciton, through a systematic dependence of the biexciton peak on excitation power, gate voltage, and temperature using steady-state and time-resolved photoluminescence (PL). With the help of a combination of the experimental data and a rate equation model, we argue that the binding energy of the charged biexciton is less than the spectral separation of its peak from the neutral exciton. We also note that while the momentum-direct radiative recombination of the neutral exciton is restricted within the light cone, such restriction is relaxed for a charged biexciton recombination due to the presence of near-parallel excited and final states in the momentum space.

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