Moiré ﬂat bands in twisted 2D hexagonal vdW materials

Abstract Moiré superlattices in twisted bilayer graphene (TBG) and its derived structures can host exotic correlated quantum phenomena because the narrow moiré ﬂat minibands in those systems effectively enhance the electron-electron interaction. Correlated phenomena are also observed in 2H-transitional metal dichalcogenides moiré superlattices. However, the number of moiré systems that have been explored in experiments are still very limited. Here we theoretically investigate a series of two-dimensional (2D) twisted bilayer hexagonal materials (TBHMs) beyond TBG at ﬁxed angles of 7.34◦ and 67.34◦ with 22 2D van der Waals (vdW) layered materials that are commonly studied in experiments. First-principles calculations are employed to systemically study the moiré minibands in these systems. We ﬁnd that ﬂat bands with narrow bandwidth generally exist in these systems. Some of the systems such as twisted bilayer In2Se3, InSe, GaSe, GaS and PtS2 even host ultra-ﬂat bands with bandwidth less than 20 meV even for such large angles, which make them especially appealing for further experimental investigations. We further analysis the characters of moiré ﬂat bands and provides guidance for further exploration of 2D moiré superlattices that could host strong electron correlations.

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

Nature Communications ◽

10.1038/s41467-021-23732-6 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Shengnan Miao ◽

Tianmeng Wang ◽

Xiong Huang ◽

Dongxue Chen ◽

Zhen Lian ◽

...

Keyword(s):

Transition Metal Dichalcogenides ◽

Strongly Correlated Electrons ◽

Optical Excitation ◽

Excitation Power ◽

Band Alignment ◽

Electron Interaction ◽

Correlated Electrons ◽

Strong Electron ◽

Correlated Electron ◽

Metal Dichalcogenides

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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Realization of electron antidoping by modulating the breathing distortion in BaBiO3

10.21203/rs.3.rs-128095/v1 ◽

2020 ◽

Author(s):

Hui Cao ◽

Hongli Guo ◽

Yu-Cheng Shao ◽

Qixin Liu ◽

Xuefei Feng ◽

...

Keyword(s):

Band Gap ◽

Oxygen Vacancies ◽

Functional Materials ◽

Electron Systems ◽

First Principles Calculations ◽

Strong Electron ◽

Correlated Electron Systems ◽

Strong Electron Correlations ◽

Correlated Electron ◽

Conduction Bands

Abstract The recent proposal of antidoping scheme breaks new ground in conceiving conversely functional materials and devices, yet the few available examples belong to the correlated electron systems. Here we demonstrate both theoretically and experimentally that the main group oxide BaBiO3 is a model system for antidoping using oxygen vacancies. The first-principles calculations show that the band gap systematically increases due to the strongly enhanced Bi-O breathing distortions away from the vacancies and the annihilation of Bi 6s/O 2p hybridized conduction bands near the vacancies. The spectroscopic experiments confirm the band gap increasing systematically with electron doping, with a maximal gap enhancement of ~75% when the film’s stoichiometry is reduced to BaBiO2.75. The Raman and diffraction experiments show the suppression of the overall breathing distortion. The study unambiguously demonstrates the remarkable antidoping effect in a material without strong electron correlations and underscores the importance of bond disproportionation in realizing such an effect.

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Parameters synergism in the preparation of TiN(100) transition layer with high structural integrity on Si(100): First‐principles calculations and experimental investigations

Surface and Interface Analysis ◽

10.1002/sia.6936 ◽

2021 ◽

Author(s):

Yang Wang ◽

Weihua Wang ◽

Guoyang Shu ◽

Shishu Fang ◽

Bing Dai ◽

...

Keyword(s):

First Principles ◽

Transition Layer ◽

Structural Integrity ◽

Experimental Investigations ◽

First Principles Calculations

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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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Fine structures of valley-polarized excitonic states in monolayer transitional metal dichalcogenides

Nanophotonics ◽

10.1515/nanoph-2020-0054 ◽

2020 ◽

Vol 9 (7) ◽

pp. 1811-1829 ◽

Cited By ~ 1

Author(s):

Zhipeng Li ◽

Tianmeng Wang ◽

Shengnan Miao ◽

Zhen Lian ◽

Su-Fei Shi

Keyword(s):

Optical Excitation ◽

Coherence Time ◽

Two Dimensions ◽

Degree Of Freedom ◽

Research Progress ◽

Many Body ◽

Transitional Metal ◽

Metal Dichalcogenides ◽

Fine Structures ◽

Excitonic States

AbstractMonolayer transitional metal dichalcogenides (TMDCs), a new class of atomically thin semiconductor, respond to optical excitation strongly with robust excitons, which stem from the reduced screening in two dimensions. These excitons also possess a new quantum degree of freedom known as valley spin, which has inspired the field of valleytronics. The strongly enhanced Coulomb interaction allows the exciton to bind with other particles to form new excitonic states. However, despite the discovery of trions, most of the excitonic states in monolayer TMDCs remain elusive until recently, when new light was shed into the fascinating excitonic fine structures with drastically improved sample quality through boron nitride encapsulation. Here, we review the latest research progress on fine structures of excitonic states in monolayer TMDCs, with a focus on tungsten-based TMDCs and related alloy. Many of the new excitonic complexes inherit the valley degree of freedom, and the valley-polarized dark excitonic states are of particular interest because of their long lifetime and possible long valley coherence time. The capability of resolving the excitonic fine structures also enables the investigation of exciton–phonon interactions. The knowledge of the interlayer between excitons and other particles not only advances our understanding of many-body effects in the monolayer TMDCs but also provides guidance on future applications based on TMDCs.

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Interplay of spin–orbit coupling and Coulomb interaction in ZnO-based electron system

Nature Communications ◽

10.1038/s41467-021-23483-4 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

D. Maryenko ◽

M. Kawamura ◽

A. Ernst ◽

V. K. Dugaev ◽

E. Ya. Sherman ◽

...

Keyword(s):

Coulomb Interaction ◽

High Mobility ◽

Electron System ◽

Orbit Coupling ◽

Electron Interaction ◽

Spin Orbit Coupling ◽

Spin Orbit ◽

Strong Electron ◽

Strongly Coupled ◽

Dimensional Electron System

AbstractSpin–orbit coupling (SOC) is pivotal for various fundamental spin-dependent phenomena in solids and their technological applications. In semiconductors, these phenomena have been so far studied in relatively weak electron–electron interaction regimes, where the single electron picture holds. However, SOC can profoundly compete against Coulomb interaction, which could lead to the emergence of unconventional electronic phases. Since SOC depends on the electric field in the crystal including contributions of itinerant electrons, electron–electron interactions can modify this coupling. Here we demonstrate the emergence of the SOC effect in a high-mobility two-dimensional electron system in a simple band structure MgZnO/ZnO semiconductor. This electron system also features strong electron–electron interaction effects. By changing the carrier density with Mg-content, we tune the SOC strength and achieve its interplay with electron–electron interaction. These systems pave a way to emergent spintronic phenomena in strong electron correlation regimes and to the formation of quasiparticles with the electron spin strongly coupled to the density.

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