题目：Exciton and Spin/Valley Properties in Transition Metal Dichalcogenide Monolayers

报告人：Xavier MARIE，Professor，National Institute of Applied Sciences (INSA- University of Toulouse，France）

时 间：2024年2月27日（周二）上午10:00

地 点：良乡校区物理实验中心229会议室

摘要：

Encapsulation of Transition Metal Dichalcogenides (TMD) monolayers in hexagonal Boron Nitride (hBN) yields narrow optical transitions approaching the homogeneous exciton linewidth [1-3]. The exciton radiative rate in these van der Waals heterostructures can be tailored by a simple change of the hBN encapsulation layer thickness as a consequence of the Purcell effect [4].

We also measured the exciton fine structure by magneto-photoluminescence spectroscopy in magnetic fields up to 30 T [5-6]. I will show that the bright-dark exciton splitting can be tuned by a few meV, as a result of a significant Lamb shift of the optically active exciton which arises from emission and absorption of virtual photons triggered by the vacuum fluctuations of the electromagnetic field [7].

Finally I will present recent experimental results on spin/valley pumping of resident electrons in WSe2 and WS2 monolayers [8]. Using a spatially-resolved optical pump-probe experiment, we measured the lateral transport of spin/valley polarized electrons over very long distances (tens of micrometers) [9]. These results highlight the key role played by the spin-valley locking effect in TMD monolayers on the pumping efficiency and the polarized electron transport.

[1] G. Wang et al, Rev. Mod. Phys. 90, 021001 (2018)

[2] F. Cadiz et al, Phys. Rev. X 7, 021026 (2017)

[3] G. Wang et al, Phys. Rev. Lett. 119, 047401 (2017)

[4] H. Fang et al, Phys. Rev. Lett. 123, 067401 (2019)

[5] C. Robert et al, Phys. Rev. Lett . 126, 067403 (2021)

[6] C. Robert et al, Nature Com. 11, 4037 (2020)

[7] L. Ren et al, Phys. Rev. Lett 131, 116901 (2023)

[8] C. Robert et al, Nature Com. 12, 5455 (2021)

[9] C. Robert et al, Phys. Rev. Lett. 129, 027402 (2022)

简历：

Xavier Marie is Professor at the National Institute of Applied Sciences (INSA- University of Toulouse). He has joined the Institut Universitaire de France (IUF) in 2005 as a Junior member and in 2015 as a Senior member.

He is currently in charge of the Laboratory of Excellence NanoX (https://nanox-toulouse.fr). which brings together 200 permanent researchers from 6 research laboratories in Toulouse. He is also the co-founder of the Quantum Institute in Occitanie Region, created in 2020 (https://iqoc.fr ).

He has worked for about 30 years on optical spectroscopy of low dimensional semiconductor structures (quantum wells, quantum dots, 2D materials). His main present interest is the optical, valley and spin properties of various van der Waals heterostructures and band structure engineering of semiconductors for optical telecommunication devices, solar cells and quantum technology devices.

He is author or co-author of about 380 papers in refereed journals, 2 books, 12 book chapters and 5 patents (h=73,>~20 000 citations, google scholar). He gave 150 invited talks in International Conferences and seminars and 15 lectures in International Summer Schools. He has been chairman or co-chairman of 10 international conferences or workshops.

He is a regular expert and member of panels for EPSRC (United Kingdom), Department of Energy (USA), DFG (Germany), SNSF (Switzerland), SFI (Ireland), ERC (Europe), CAS (China), ANR (France)...

He has been a member of the editorial board of Physical Review X (American Physics Society) since 2018 and a member of the International Union of Pure and Applied Physics (IUPAP), since 2021.

He received the Jean Ricard prize from the French Society of Physics in 2019, the “Palmes Académiques-Officer” 2020 and is one of the highly Cited Researcher in 2021, 2022 and 2023 (Web of Science, Clarivate).

联系方式：gw@bit.edu.cn

邀请人： 王刚 教授

网 址：/

承办单位：物理学院、先进光电量子结构设计与测量教育部重点实验室

*Title：Exciton and Spin/Valley Properties in Transition Metal Dichalcogenide Monolayers

*Reporter：Xavier MARIE，Professor，National Institute of Applied Sciences (INSA- University of Toulouse，France）

*Time：Feb. 27th , 2024 (Tuesday) 10:00am

*Place：Room 229 Physics Experiment Center, Liangxiang Campus

*Contact Person: Gang Wang, Professor, gw@bit.edu.cn

*Abstract:

Encapsulation of Transition Metal Dichalcogenides (TMD) monolayers in hexagonal Boron Nitride (hBN) yields narrow optical transitions approaching the homogeneous exciton linewidth [1-3]. The exciton radiative rate in these van der Waals heterostructures can be tailored by a simple change of the hBN encapsulation layer thickness as a consequence of the Purcell effect [4].

We also measured the exciton fine structure by magneto-photoluminescence spectroscopy in magnetic fields up to 30 T [5-6]. I will show that the bright-dark exciton splitting can be tuned by a few meV, as a result of a significant Lamb shift of the optically active exciton which arises from emission and absorption of virtual photons triggered by the vacuum fluctuations of the electromagnetic field [7].

Finally I will present recent experimental results on spin/valley pumping of resident electrons in WSe2 and WS2 monolayers [8]. Using a spatially-resolved optical pump-probe experiment, we measured the lateral transport of spin/valley polarized electrons over very long distances (tens of micrometers) [9]. These results highlight the key role played by the spin-valley locking effect in TMD monolayers on the pumping efficiency and the polarized electron transport.

[1] G. Wang et al, Rev. Mod. Phys. 90, 021001 (2018)

[2] F. Cadiz et al, Phys. Rev. X 7, 021026 (2017)

[3] G. Wang et al, Phys. Rev. Lett. 119, 047401 (2017)

[4] H. Fang et al, Phys. Rev. Lett. 123, 067401 (2019)

[5] C. Robert et al, Phys. Rev. Lett . 126, 067403 (2021)

[6] C. Robert et al, Nature Com. 11, 4037 (2020)

[7] L. Ren et al, Phys. Rev. Lett 131, 116901 (2023)

[8] C. Robert et al, Nature Com. 12, 5455 (2021)

[9] C. Robert et al, Phys. Rev. Lett. 129, 027402 (2022)

*Profile：

Xavier Marie is Professor at the National Institute of Applied Sciences (INSA- University of Toulouse). He has joined the Institut Universitaire de France (IUF) in 2005 as a Junior member and in 2015 as a Senior member.

He is currently in charge of the Laboratory of Excellence NanoX (https://nanox-toulouse.fr). which brings together 200 permanent researchers from 6 research laboratories in Toulouse. He is also the co-founder of the Quantum Institute in Occitanie Region, created in 2020 (https://iqoc.fr ).

He has worked for about 30 years on optical spectroscopy of low dimensional semiconductor structures (quantum wells, quantum dots, 2D materials). His main present interest is the optical, valley and spin properties of various van der Waals heterostructures and band structure engineering of semiconductors for optical telecommunication devices, solar cells and quantum technology devices.

He is author or co-author of about 380 papers in refereed journals, 2 books, 12 book chapters and 5 patents (h=73,>~20 000 citations, google scholar). He gave 150 invited talks in International Conferences and seminars and 15 lectures in International Summer Schools. He has been chairman or co-chairman of 10 international conferences or workshops.

He is a regular expert and member of panels for EPSRC (United Kingdom), Department of Energy (USA), DFG (Germany), SNSF (Switzerland), SFI (Ireland), ERC (Europe), CAS (China), ANR (France)...

He has been a member of the editorial board of Physical Review X (American Physics Society) since 2018 and a member of the International Union of Pure and Applied Physics (IUPAP), since 2021.

He received the Jean Ricard prize from the French Society of Physics in 2019, the “Palmes Académiques-Officer” 2020 and is one of the highly Cited Researcher in 2021, 2022 and 2023 (Web of Science, Clarivate).