層間轉(zhuǎn)角角度決定了莫爾布里淵區(qū)（MBZ）與單層晶胞布里淵區(qū)（UBZs）之間的關(guān)聯(lián)，引發(fā)了相關(guān)的莫爾勢。這導(dǎo)致了在UBZs中具有不同動量態(tài)之間的光允許電子–空穴躍遷，這可能與吸收過程中激子的精細(xì)結(jié)構(gòu)有關(guān)。為了對激子結(jié)構(gòu)與轉(zhuǎn)角角度之間關(guān)系進(jìn)行全面理解，需要對轉(zhuǎn)角結(jié)構(gòu)中的激子進(jìn)行基于GW-BSE的多體微擾理論分析。

來自印度科學(xué)研究所物理系凝聚態(tài)理論中心的Sudipta Kundu等，提出了一種使用GW-BSE研究TMD異質(zhì)結(jié)中雙層轉(zhuǎn)角角度對激子性質(zhì)和光學(xué)選擇規(guī)則影響的方法。作者在一個相對旋轉(zhuǎn)角度為16°的轉(zhuǎn)角MoS₂/MoSe₂異質(zhì)結(jié)構(gòu)上演示了其方法，該結(jié)構(gòu)允許在UBZs中不同高對稱點之間發(fā)生躍遷，由原子重構(gòu)和層間不匹配確定。通過分析，作者揭示了一種獨特的動量混合激子性質(zhì)，其狀態(tài)由層間和層內(nèi)電子–空穴激發(fā)組成。?

這些結(jié)果指出了動量直接激子和光學(xué)活躍激子的一般性質(zhì)，其混合了層UBZs中的不同點，并且在較小的角度下同樣有效。這一結(jié)果表明，激子性質(zhì)和光譜特征與轉(zhuǎn)角的TMD異質(zhì)結(jié)構(gòu)的底層結(jié)構(gòu)之間存在直接的關(guān)系，可為通過選擇層間轉(zhuǎn)角角度來調(diào)節(jié)激子性質(zhì)提供了潛在可能性。該文最近發(fā)布于npj Computational Materials 9: 186 (2023).?

Editorial Summary

Moiré patterns generated due to a lattice mismatch between layers of two-dimensional materials serve as an emerging platform for novel correlated electronic and excitonic physics. In particular, twisted heterostructures of transition metal dichalcogenides (TMDs) with a type-II band alignment hold intriguing optical properties due to the varying exciton localization associated with the twist-induced moiré potential. The interlayer twist angle dictates the relation between the moiré Brillouin Zone (MBZ) and the unit-cell Brillouin Zones (UBZs) of the separate layers, inducing an associated moiré potential. This leads to optically-allowed electron-hole transitions between states of different momenta in the UBZs, which can be associated with the exciton fine structure in absorption. A full GW-BSE based many-body theory analysis of excitons in the twisted structure is required for a general ab initio understanding of the relation between the twist angle and the exciton structure.

Sudipta Kundu et al. from the Centre for Condensed Matter Theory, Department of Physics, Indian Institute of Science, presented an approach to study the effect of twist angle on the exciton nature and optical selection rules in TMD hetero-bilayers by using GW-BSE. They demonstrated their approach on a twisted MoS₂/MoSe₂heterostructure with a relative rotation angle of 16°, which allows transitions between distinct high-symmetry points in the UBZs, determined by the atomic reconstruction and interlayer mismatch. Analyses reveal a unique momentum-mixed excitonic nature, with states that are comprised of both inter- and intra-layer electron-hole excitations. These results point to a general property of momentum-direct and optically-active excitons that mix different points in the layer UBZs, and is valid at smaller angles as well. Their findings suggest a direct relation between exciton nature and spectral features to the underlying structure in twisted TMD heterostructures, offering potential tunability of excitonic properties upon the choice of interlayer twist angle. This article was recently published in npj Computational Materials?9:?186?(2023).

原文Abstract及其翻譯

Exciton fine structure in twisted transition metal dichalcogenide heterostructures （轉(zhuǎn)角過渡金屬硫化物異質(zhì)結(jié)構(gòu)中的激子精細(xì)結(jié)構(gòu)）

Sudipta Kundu,?Tomer Amit,?H. R. Krishnamurthy,?Manish Jain?&?Sivan Refaely-Abramson?

Abstract?Moiré superlattices of transition metal dichalcogenide (TMD) heterostructures give rise to rich excitonic phenomena associated with the interlayer twist angle. Theoretical calculations of excitons in such systems are typically based on model moiré potentials that mitigate the computational cost. However, predictive understanding of the electron-hole coupling dominating the excitations is crucial to realize the twist-induced modifications of the optical selection rules. In this work, we use many-body perturbation theory to evaluate the relation between twist angle and exciton properties in TMD heterostructures. We present an approach for unfolding excitonic states from the moiré Brillouin zone onto the separate-layer ones. Applying this method to a large-angle twisted MoS₂/MoSe₂?bilayer, we find that the optical spectrum is dominated by mixed electron–hole transitions with different momenta in the separate monolayers, leading to unexpected hybridization between interlayer and intralayer excitons. Our findings offer a design pathway for exciton layer-localization in TMD heterostructures.

摘要過渡金屬硫化物（TMD）異質(zhì)結(jié)構(gòu)的莫爾超晶格引起了與層間轉(zhuǎn)角相關(guān)豐富的激子現(xiàn)象。此類系統(tǒng)中激子的理論計算通?；谀Ｐ湍獱杽荩瑥亩档陀嬎愠杀?。然而，對主導(dǎo)激發(fā)的電子–空穴耦合的預(yù)測性理解，對于實現(xiàn)光學(xué)選擇規(guī)則扭轉(zhuǎn)引起的修改至關(guān)重要。在本工作中，我們使用多體微擾理論評估了TMD異質(zhì)結(jié)構(gòu)中的轉(zhuǎn)角和激子性質(zhì)之間的關(guān)系。我們提出了一種從莫爾布里淵區(qū)展開激子態(tài)到單獨層的方法。將這種方法應(yīng)用于大角度扭曲的MoS₂/MoSe₂雙層，我們發(fā)現(xiàn)，光譜主要由在單獨單層中具有不同動量的混合電子–空穴躍遷主導(dǎo)，導(dǎo)致層間和層內(nèi)激子之間的意外雜化。我們的發(fā)現(xiàn)為TMD異質(zhì)結(jié)構(gòu)中的激子層定位提供了設(shè)計途徑。?