SCHOOL 2020 – ICFO FRONTIERS

ICFO-MIT School on the Frontiers of Light

Online Symposium on “Emergent phenomena in Moiré materials”
6-17 July 2020, Barcelona

ONLINE SYMPOSIUM ON “EMERGENT PHENOMENA IN MOIRE MATERIALS”

Overview

Moiré systems with 2D materials offer a novel platform for exploring a plethora of exotic phenomena. The emerging field of twistronics embodies a fundamentally new approach to engineering the electronic and optical properties of materials and devices. A tantalising example is the so-called magic angle rotation between sheets of graphene or semi-conducting 2D materials, which has shown superconducting phases similar to those of unconventional high-Tc materials. The wide tunability of Moiré systems offers many exciting new possibilities to explore.

This year, due the evolving COVID-19 situation, for the first time the ICFO – MIT Schools on the Frontiers of Light will be held online with sessions spread out over 2 weeks, and they’re are open to all interested attendees.

The sessions gather leading experimentalists and theorists, and will cover the optics and electronics of twisted 2D materials: Twistronics, Correlated electron systems, Excitonics, Mott insulators, Polaritonics, Superconductivity, Magnetism, Topology, etc.

The online event will include seminars, round table discussions, hot topics sessions and poster session, where students will have the opportunity to interact and present their current research.

¡NEW! SPIE@ICFO CHAIR RESEARCH FELLOWSHIPS

Call for internship positions launched within the recently announced SPIE@ICFO Chair for Diversity in Photonic Sciences.

Two fellowships are available for outstanding international undergraduate and masters students to conduct a Research Internship, Bachelor or Master Thesis with an ICFO research group, with preference given to students from developing countries.

Link to call

REGISTRATION FOR ICFO-MIT SCHOOLS ON THE FRONTIERS OF LIGHT

If you would like to attend one or more seminars of the online school, please register HERE.

During the 2-week Symposium, we will update you with information regarding the sessions and will email you the links to join in.

Program

	SEMINAR 3PM-4:15PM CEST	SEMINAR 4:30PM-17:45PM CEST	COMMUNITY 6M-7PM CEST
Monday 6 July	Dr. Allan MacDonald (Texas University) Moiré Magic JOIN IN: http://s.ic.fo/AllanMacDonald060720	Dr. Ali Yazdani (Princeton University) Strongly Interacting Electronic States of a Moiré Superlattice JOIN IN: http://s.ic.fo/AliYazdani060720	Poster Pitch Session JOIN IN: http://s.ic.fo/PosterPitchSession060720 + Online Town JOIN IN: http://s.ic.fo/OnlineTown060720
Tuesday 7 July	Dr. Xavier Marie (INSA Toulouse) Excitons in Transition Metal Dichalcogenide Mono- and Bi-layers JOIN IN: http://s.ic.fo/XavierMarie070720	Dr. Paco Guinea (IMDEA Madrid) Electronic structure and interactions in narrow bands in stacks of two-dimensional materials JOIN IN: http://s.ic.fo/PacoGuinea070720	Poster Pitch Session JOIN IN: http://s.ic.fo/PosterPitchSession070720 + Online Town JOIN IN: http://s.ic.fo/OnlineTown070720
Wednesday 8 July	Dr. Andrei Bernevig (Princeton University) Single Particle and Many-Body Phase Diagram of Twisted Bilayer Graphene JOIN IN: http://s.ic.fo/AndreiBernevig080720	Dr. Eli Zeldov (Weizmann Institute) Mapping the twist-angle disorder and unconventional Landau levels in magic angle graphene JOIN IN: http://s.ic.fo/EliZeldov080720	Hot Topics JOIN IN: http://s.ic.fo/HotTopicsSession080720 Download Program: http://frontiers.icfo.eu/wp-content/uploads/2020/07/WED-8-JULY-Hot-Topics-1.pdf
Thursday 9 July	Dr. James Hone (Columbia University) Tunable electronic and optical properties in rotatable heterostructures JOIN IN: http://s.ic.fo/JamesHone090720	Dr. Ashvin Vishwanath (Harvard University) Skyrmion superconductivity and the insulating ground state of magic angle graphene JOIN IN: http://s.ic.fo/AshvinVishwanath090720
Friday 10 July	Dr. Dimitri Basov (Columbia University) Multi-messenger nano-imaging of electrons, polaritons, phonons and excitons in Moire superlattices JOIN IN: http://s.ic.fo/DimitriBasov100720	Dr. Marco Polini (University of Pisa) Collective excitations in twisted bilayer graphene JOIN IN: http://s.ic.fo/MarcoPolini100720	Dr. Tobias Roedel (Nature Editor) Q&A with a Nature editor JOIN IN: http://s.ic.fo/Nature100720

	SEMINAR 3PM-4:15PM CEST	SEMINAR 4:30PM-17:45PM CEST	COMMUNITY 6M-7PM CEST
Monday 13 July	Dr. Eva Andrei (Rutgers University) The magic of atomically thin crystals JOIN IN: http://s.ic.fo/EvaAndrei130720	Dr. Leni Bascones (ICMM Madrid) Interactions in twisted bilayer graphene JOIN IN: http://s.ic.fo/LeniBascones130720	Poster Pitch Session JOIN IN: http://s.ic.fo/PosterPitchSession130720 + Online Town JOIN IN: http://s.ic.fo/OnlineTown130720
Tuesday 14 July	Dr. Atac Imamoglu (ETH Zurich) Signatures of correlated electrons in a moiré superlattice in exciton spectrum JOIN IN: http://s.ic.fo/AtacImamoglu140720	Dr. Rafael Fernandes (University of Minnesota) Electronic nematicity in moiré superlattices JOIN IN: http://s.ic.fo/RafaelFernandez140720	Poster Pitch Session JOIN IN: http://s.ic.fo/PosterPitchSession140720 + Online Town JOIN IN: http://s.ic.fo/OnlineTown140720
Wednesday 15 July	Dr. Senthil Todadri (MIT) Topology and correlations in graphene Moiré lattices JOIN IN: http://s.ic.fo/SenthilTodadri150720	Dr. Jeanie Lau (Ohio State University) Flat Bands in Flatlands JOIN IN: http://s.ic.fo/JeanieLau150720	Contributed Talks JOIN IN: http://s.ic.fo/ContributedTalks150720 Download Program: http://frontiers.icfo.eu/wp-content/uploads/2020/07/WED-15-JULY-Contributed-Talks.pdf + Online Town JOIN IN: http://s.ic.fo/OnlineTown150720
Thursday 16 July	Dr. Tobias Stauber (CSIC Instituto de Ciencia de Materiales de Madrid ) Superconductivity and chirality in twisted bilayer graphene JOIN IN: http://s.ic.fo/TobiasStauber160720	Dr. Jie Shan (Cornell University) Strong correlation physics in semiconductor moiré superlattices JOIN IN: http://s.ic.fo/JieShan160720
Friday 17 July	Dr. Pablo Jarillo-Herrero (MIT) Competing orders and phase transition in magic-angle graphene JOIN IN: http://s.ic.fo/PabloJarillo-Herrero170720	Round Table Discussion Dr. Maciej Lewenstein, Dr. Dmitri Efetov, Dr. Frank Koppens and Dr. Pablo Jarillo-Herrero Moderator: Dr. Antoine Reserbat-Plantey JOIN IN: http://s.ic.fo/RoundTable170720

THE SEMINAR VIDEOS NOW ARE AVAILABLE ONLINE

If you missed a talk or if you want to rewatch it, you will find the seminar videos online.

You are welcome to contribute with your questions and comments or join a discussion.

WATCH SEMINAR VIDEOS

Abstracts

Ali Yazdani

Strongly Interacting Electronic States of a Moiré Superlattice

By Dr. Ali Yazdani (Princeton University)

Monday, July 6th 16:30 – 17:45 CEST

Link to join in: http://s.ic.fo/AliYazdani060720

ABSTRACT

Interactions among electrons or the topology of their energy bands can create novel quantum phases of matter. The discovery of electronic bands with flat energy dispersion in magic-angle twisted bilayer graphene (MATBG) has created a unique opportunity to search for new correlated and topological electronic phases. From the initial discovery of correlated insulators, superconductivity, and more recent reports of topological phases in various transport studies it is clear that this is a very rich electronic system. To understand the underlying mechanism for formation of various phases and their properties, we have carried out a series of scanning tunneling microscopy (STM) and spectroscopy (STS) of MATBG while tuning its carrier concentration with a gate. Such density-tuned STS (DT-STS) studies can reveal a variety of key information that are impossible to obtain from other techniques. For example, in our first study, we showed that while the properties of the flat bands in MATBG can be understood with a weakly interacting picture when they are fully occupied or empty, at partial filling such models fails to understand their spectroscopic properties. [1] In a subsequent study, we showed that within this highly interacting states there are a cascade of transition occurring as a function of carrier density, at each integer filling—where insulating phases form at low temperatures. [2] We understand these transitions as a direct consequence of Coulomb interactions and spin/valley quantum degeneracy of this systems splitting the degenerate flat bands into Hubbard sub-bands. I will describe these studies as well as our ongoing efforts to probe the nature insulating, topological, and superconducting states In MATBG using millikelvin STM measurements.

[1] Y. Xie. et al. Nature 572, 101–105 (2019).
[2] D. Wong, et al. Nature 582, pages198–202(2020).

BIO

Ali Yazdani’s research program focuses on the development and application of novel experimental methods to directly visualize exotic electronic phenomena in solids.. Yazdani received his Ph.D. from Stanford University in 1995, after which he was postdoctoral scientist at IBM’s Almaden Research Center in California (1995-1997). After working at IBM, Yazdani went on to establish his research program as a faculty member at the University of Illinois at Urbana-Champaign in 1997. In 2005, he joined the physics faculty at Princeton University and in 2015 was named the Class of 1909 Professor of Physics and is also the Director of the Princeton Center for Complex Materials, an NSF supported Materials Research Science and Engineering Center. He is a member of the National Academy of Sciences (2019), fellow of the American Academy of Arts and Science (2015), fellow of the American Association for Advancement of Science (2012), and fellow of the American Physical Society (2009). He has also received a Humboldt Research award, an NSF CAREER award, and was a Sloan Fellow. He is currently a Betty and Gordon Moore Foundation experimental investigator in quantum materials. He has held a number of lectureships including being a Leob Lectures at Harvard, a Lamb Lecturer at the Max Planck Insitute in Sttutgart, an Einstein Lecturer at the Weizmann Institute, Israel, a Pagels Lecturer at the Aspen Center for Physics, a Kavli Lecturer at the Delft Institute of Technology, Netherlands and a Joliot Chair, École Supérieure de Physique et de Chimie Industrielles de la ville de Paris. Professor Yazdani has held a number of visiting positions, including being a Visiting Fellow at Trinity College in Cambridge, UK (2019-2020).

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

https://www.nature.com/articles/s41586-020-2339-0

https://www.nature.com/articles/s41586-019-1422-x

Allan MacDonalld

Moiré Magic

By Dr. Allan H. MacDonald (Texas University)

Monday, July 6th 15:00 – 16:15 CEST

Link to join in: http://s.ic.fo/AllanMacDonald060720

ABSTRACT

Two-dimensional crystal bilayers form periodic moiré patterns when overlaid with a small difference in lattice constant or orientation. Research over the past couple of years has established artificial moiré crystals as a powerful platform for strongly correlated electron and exciton physics. The possibility of accurate in situ tuning of the number of electrons per period over the full range of band filling simply by using electrical gates provides has provided an unprecedented window into the richness of strongly correlated quantum matter, with superconductors, Mott insulators, Chern insulators, and density-wave states occurring in the same material under different gating or twisting conditions.

After briefly surveying the properties of twisted graphene and transition metal dichalcogenide bilayers, the moiré systems that have been most fully developed to date, I will focus on two aspects of magic-angle twisted bilayer graphene (MATBG), namely its Chern insulator states, and its superconductivity. The Chern insulator state of MATBG is realized by momentum-space condensation and in this sense is distinct from the previously realized Chern insulators states in magnetically doped topological insulators. One interesting consequence that I will discuss is hysteretic behavior as a function of gate voltage in the presence of a weak magnetic field – a type of electrical control of magnetism that has not been realized previously. The superconducting state of MATBG is, as is common in strongly-correlated superconductors, still somewhat mysterious. I will discuss some aspects of superconductivity and linear-in-T resistivity in MATBG.

BIO

Allan H. MacDonald received his B.Sc. from St. Francis Xavier University, Antigonish, Nova Scotia, Canada in 1973, and a Ph.D. degrees in physics from the University of Toronto in 1978. He was a member of the research staff of the National Research Council of Canada and has taught at Indiana University and the University of Texas at Austin.

He has contributed to research on electronic structure theory, the quantum Hall effect, magnetism, and superconductivity, among a variety of other topics.

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

Nature of the correlated insulator states in twisted bilayer graphene.

M Xie, AH MacDonaldPhysical Review Letters 124 (9), 097601

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.097601

B. Andrei Bernevig

Single Particle and Many-Body Phase Diagram of Twisted Bilayer Graphene

By Dr. B. Andrei Bernevig (Princeton University)

Wednesday 8 July, 15:00 – 16:15 CEST

Link to join in: http://s.ic.fo/AndreiBernevig080720

ABSTRACT

I will review several physical phenomena in TBLG lattices with an emphasis on discovering the topological properties of the bands and their influence on the superconducting state.

BIO

Born: 1978 (age 41 years), Bucharest, Romania

Education: Stanford University (2006)

Books: Topological Insulators and Topological Superconductors

Awards: New Horizons in Physics Prize, Guggenheim Fellowship for Natural Sciences, US & Canada

Ashvin Vishwanath

Skyrmion superconductivity and the insulating ground state of magic angle graphene

By Dr. Ashvin Vishwanath (Harvard University)

Thursday 9 July, 16:30 – 17:45 CEST

Link to join in: http://s.ic.fo/AshvinVishwanath090720

ABSTRACT

We propose a topological mechanism for the observed superconductivity in magic angle graphene, that ties the superconductor to the interaction-driven insulating phases. Specifically, we show that a promising candidate for an ordered insulating phase has the property that skyrmions in its order parameter carry electric charge. Skyrmion condensation can then lead to a superconductor – whose properties we calculate within the theory.

BIO

Ashvin Vishwanath is a condensed matter theorist known for his foundational work on Weyl semimetals, strongly interacting topological states beyond the single particle paradigm and `non-Landau’ quantum phase transitions.

Atac Imamoglu

Signatures of correlated electrons in a moiré superlattice in exciton spectrum

By. Dr. Atac Imamoglu (ETH Zurich)

Tuesday 14 July, 15:00 – 16:15 CEST

Link to join in: http://s.ic.fo/AtacImamoglu140720

ABSTRACT

Signatures of correlated electrons in a moiré superlattice in exciton spectrum

Yuya Shimazaki¹, Ido Schwartz¹, Kenji Watanabe², Takashi Taniguchi², Clemens Kuhlenkamp¹, Tomasz Smolenski¹, Martin Kroner¹, Atac Imamoglu¹

¹ Department of Physics, Institute for Quantum Electronics, ETH Zurich, Zurich 8093, Switzerland

² National Institute for Materials Science, Ibaraki 305-0044, Japan

imamoglu@phys.ethz.ch

2D material moiré heterostructure constitute a novel platform to study many body physics of electrons and excitons. Transport study of twisted bilayer graphene revealed rich exotic phase of electrons including Mott insulator state, superconductivity, strange metal, and ferromagnetism [1, 2]. On the other hand, optical spectroscopy study revealed the effect of moiré lattice potential on excitons in transition metal dichalcogenide (TMD) heterostructure [3], but the correlated phase of electrons has been elusive.

In this talk, I will present resonant optical measurements on homo-bilayer TMD moiré heterostructure, and report the observation of strongly correlated incompressible electronic states as well as hybrid dipolar excitons [4]. We utilized a boron nitride (hBN) encapsulated MoSe₂ / hBN (1L) / MoSe₂ heterostructure which has top and bottom gate (Fig. 1a). Using top and bottom gate, we can control the chemical potential and the electric field (band alignment) independently. Tightly bound excitons in TMD interact with Fermi sea carriers by forming exciton-polaron [5], and we utilized the energy shift of exciton-polaron resonance to detect layer resolved charge configuration by optical means. In low electron density regime, we found periodic chemical potential dependence of carrier filling behavior indicating existence of moiré subband structure, and estimated that the twist angle of MoSe₂ layers is about 0.8 degree (Fig. 1b). By analyzing interlayer charge transfer behavior between top and bottom MoSe₂ while tuning electric field, we figured out abrupt interlayer charge transfer happens at specific filling around (1 electron / moiré unit cell), evidencing the emergence of strongly correlated incompressible electronic state (Fig. 1c). We also observe interlayer exciton hybridizing with intralayer exciton in neutral regime, and the fine energy splitting of interlayer exciton is consistent with moiré potential induced Umklapp scattering.

This highly tunable twisted MoSe₂ homo bilayer system separated by a monolayer hBN barrier with weak moiré potential, provides a promising platform for investigating strongly correlated Mott-Wigner physics as well as hybrid excitons. In particular, this structure could be used to study Bose-Fermi mixture constituting of strongly correlated electrons interacting with dense excitons and polaritons, and is expected to provide rich playground for many body physics.

References

[1] Y. Cao et al., Nature, 556 43 (2018).

[2] X. Lu et al., Nature, 574 653 (2019).

[3] K. L. Seyler et al., Nature, 567 66 (2019)., K. Tran et al., Nature, 567 71 (2019)., C. Jin et al., Nature, 567 76 (2019)., E. M. Alexeev et al., Nature, 567 81 (2019).

[4] Y. Shimazaki et al., Nature, 580 472 (2020).

[5] M. Sidler et al., Nature Physics, 13 255 (2017).

BIO

Atac Imamoglu received his PhD from Stanford University in 1991. He joined the faculty of University of California, Santa Barbara in 1993. In 2002 he moved to ETH Zurich as a professor of physics where he currently leads the quantum photonics group. His research interests cover quantum optics and condensed matter physics.

Figure 1. (a) Schematic sketch of the device structure. (b) Layer contrasted carrier filling behavior monitored by repulsive exciton-polaron resonance energy shift. and correspond to the axes of electric field and chemical potential. (c) Difference of exciton-polaron resonance energy between top and bottom layers, highlighting charge imbalance between top and bottom layers.

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

Strongly correlated electrons and hybrid excitons in a moiré heterostructure.

Nature, vol. 580: no. 7804, pp. 472-477, 2020

https://doi.org/10.1038/s41586-020-2191-2

Dimitri Basov

Multi-messenger nano-imaging of electrons, polaritons, phonons and excitons in Moire superlattices

By. Dr. Dimitri Basov (Columbia University)

Friday 10 July, 15:00 – 16:15 CEST

Link to join in: http://s.ic.fo/DimitriBasov100720

ABSTRACT

D.N. Basov Columbia University, http://infrared.cni.columbia.edu

I will describe a series of nano-imaging experiments aimed at visualizing rich electronic, lattice, polaritonic and excitonic phenomena in Moire superlattices of van der Waals materials. Central to our ability to visualize these effects is multi-messenger nano-imaging: a scanning probe approach for correlating in time and space images produced by diverse contrast mechanisms and carrying complementary massages about the studied phenomena.

A.S. McLeod, J. Zhang, M. Q. Gu , Feng Jin, G. Zhang , K. W. Post, X. G. Zhao, A. J. Millis, Wenbin Wu, J. M. Rondinelli, R. D. Averitt, & D. N. Basov “Multi-messenger nano-probes of hidden magnetism in a strained manganite” Nature Materials 19, 397 (2020).

Sai S. Sunku, Alexander S. McLeod, Tobias Stauber, Hyobin Yoo, Dorri Halbertal, Guangxin Ni, Aaron Sternbach, Bor-Yuan Jiang, Takashi Taniguchi, Kenji Watanabe, Philip Kim, Michael M. Fogler, and D. N. Basov “Nano-photocurrent Mapping of Local Electronic Structure in Twisted Bilayer Graphene” Nano Lett. 20, 2958 (2020).

J. McGilly, A. Kerelsky, N. R. Finney, K. Shapovalov, E.-M. Shih, A. Ghiotto, Y. Zeng, S. L. Moore, W. Wu, Y. Bai, K. Watanabe, T. Taniguchi, M. Stengel, L. Zhou, J. Hone, X.-Y. Zhu, D. N. Basov, C. Dean, C. E. Dreyer, and A. N. Pasupathy “Seeing mire superlattices”, Nature Nanotechnology 2020. arXiv:1912.06629

Yusong Bai, Lin Zhou, Jue Wang, Wenjing Wu, Leo McGilly, Dorri Halbertal, Chiu Fan, B. Lo, Fang Liu, Jenny Ardelean, Pasqual Rivera, Nathan R. Finney, Xuchen Yang, Dmitri N. Basov, Wang Yao, Xiaodong Xu, James Hone, Abhay Pasupathy, Xiaoyang Zhu “One-Dimensional Moiré Excitons in Transition-Metal Dichalcogenide Heterobilayers” Nature Materials (2020) arXiv:1912.06628

BIO

Dmitri N. Basov (PhD 1991) is a Higgins professor and Chair of the Department of Physics at Columbia University [http://infrared.cni.columbia.edu], the Director of the DOE Energy Frontiers Research Center on Programmable Quantum Materials and co-director of Max Planck Society – New York Center for Nonequilibrium Quantum Phenomena. He has served as a professor (1997-2016) and Chair (2010-2015) of Physics, University of California San Diego. Research interests include: physics of quantum materials, superconductivity, two-dimensional materials, infrared nano-optics. Prizes and recognitions: Sloan Fellowship (1999), Genzel Prize (2014), Humboldt research award (2009), Frank Isakson Prize, American Physical Society (2012), Moore Investigator (2014, 2020), K.J. Button Prize (2019), Vannevar Bush Faculty Fellowship (U.S. Department of Defense, 2019), National Academy of Sciences (2020).

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

arXiv:1911.00007v2

Eli Zeldov

Mapping the twist-angle disorder and unconventional Landau levels in magic angle graphene

By. Dr. Eli Zeldov (Weizmann Institute)

Wednesday 8 July, 16:30 – 17:45 CEST

Link to join in: http://s.ic.fo/EliZeldov080720

ABSTRACT

The emergence of flat bands and of strongly correlated and superconducting phases in twisted bilayer graphene crucially depends on the interlayer twist angle upon approaching the magic angle. Utilizing a scanning nanoSQUID-on-tip, we attain tomographic imaging of the Landau levels and derive nanoscale high precision maps of the twist-angle disorder in high quality hBN encapsulated devices, which reveal substantial twist-angle gradients and a network of jumps [1]. We show that the twist-angle gradients generate large gate tunable in-plane electric fields, unscreened even in the metallic regions, which drastically alter the quantum Hall state by forming edge channels in the bulk of the samples. The correlated states are found to be particularly fragile with respect to twist-angle disorder. We establish the twist-angle disorder as a fundamentally new kind of disorder, which alters the local band structure and may significantly affect the correlated and superconducting states.

[1] A. Uri, S. Grover, Y. Cao, J. A. Crosse, K. Bagani, D. Rodan-Legrain, Y. Myasoedov, K. Watanabe, T. Taniguchi, P. Moon, M. Koshino, P. Jarillo-Herrero, and E. Zeldov, Nature 581, 47 (2020).

BIO

Born in Riga, Latvia, he received his BSc and PhD from the Technion – Israel Institute of Technology, carried out his postdoc at IBM – Yorktown Heights, NY, and joined Weizmann Institute of Science in 1992. Eli Zeldov is an expert in superconductivity and vortex matter in superconductors. In recent years he has focused on development of new tools for magnetic and thermal imaging for study of condensed matter systems. In particular, he has developed nanoSQUID-on-tip that reaches single spin sensitivity and scanning cryogenic nanothermometry with µK sensitivity. His current research interests include vortex dynamics, dissipation and magnetism in quantum states of matter, and van der Waals materials.

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

Nanoscale imaging of equilibrium quantum Hall edge currents and of the magnetic monopole response in graphene
Aviram Uri, Youngwook Kim, Kousik Bagani, Cyprian K. Lewandowski, Sameer Grover, Nadav Auerbach, Ella O. Lachman, Yuri Myasoedov, Takashi Taniguchi, Kenji Watanabe, Jurgen Smet, and Eli Zeldov
Nature Physics 16, 164 (2020)

https://arxiv.org/abs/1908.02466

https://www.nature.com/articles/s41567-019-0713-3

Eva Andrei

The magic of atomically thin crystals

By. Dr. Eva Andre (Rutgers University)

Monday 13 July, 15:00 – 16:15 CEST

Link to join in: http://s.ic.fo/EvaAndrei130720

ABSTRACT

The discovery of two dimensional (2D) atomically thin crystals has made it possible for the first time to tune the electronic properties of a material without changing its chemical composition, for example by introducing strain1, plucking out atoms2,3, or intentionally stacking 2D crystals in various ways. One of the simplest techniques, changing the relative orientation of superposed 2D crystals, makes it possible to control the electronic band-structure with a mere twist4. In particular, by tuning the twist between two stacked graphene layers to a “magic” angle, one can create nearly flat electronic bands where the enhanced Coulomb interactions favor the emergence of correlated states that alternate between superconducting, ferromagnetic or nematic5 phases. More recently, the discovery of flat bands in grapehene membranes that underwent a buckling transition6, points the way to more robust strategies for inducing correlated phases without the requirement of fine tuning. In this talk I will cover highlights of this rapidly evolving field from its serendipitous discovery4 to recent developments.

1. Visualizing Strain-Induced Pseudo Magnetic Fields in Graphene through an hBN Magnifying Glass,Y. Jiang, J. Mao, J. Duan, X. Lai, K. Watanabe, T. Taniguchi, Francois M. Peeters and Eva Y. Andrei, Nano Letters, 17 , (2017) 2839
2. Realization of a Tunable Artificial Atom at a Charged Vacancy in Graphene, J. Mao, Y. Jiang, D. Moldovan, G. Li, K. Watanabe, T. Taniguchi, M. Ramezani Masir, F. M. Peeters, E. Y. Andrei, Nature Physics 2 (2016) 545
3. Inducing Kondo screening at point defects in graphene with gating and local curvature, Y. Jiang, J. Mao, Po-Wei Lo, D. May, G. Li, G-Yu Guo, F. B. Anders, K. Watanabe, T. Taniguchi, F. and E.Y. Andrei, Nature Communocations 9 (2018) 2349
4. Observation of Van Hove singularities in twisted graphene layers, G. Li, et al , Nature Physics. 6 (2010) 109 5. Charge-ordering and broken rotational symmetry in magic angle twisted bilayer , Y. Jiang, J. Mao, X. Lai, K. Watanabe, T. Taniguchi, K. Haule and E.Y. Andrei, Nature, 573 (2019) 91.
6. Evidence of Flat Bands and Correlated States in Buckled Graphene Superlattices, J. Mao,et al arXiv:2006.01660, Nature in print (2020)

BIO

Eva Y. Andrei is an experimental condensed matter physicist known for her work on low dimensional systems, including 2D Wigner crystals, vortex lattices in superconductors, and the electronic properties of graphene. Andrei is the Board of Governors chaired professor in the department of Physics and Astronomy at Rutgers University and is currently a Betty and Gordon Moore Foundation experimental investigator in quantum materials. She is a fellow of the National Academy of Sciences, the American Academy of Arts and Sciences, the American Physical Society and the American Association for the Advancement of Science. Andrei is currently serving as Chair of the Division of Condensed Matter Physics of the American Physical Society.

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

Charge-ordering and broken rotational symmetry in magic angle twisted bilayer , Y. Jiang, J. Mao, X. Lai, K. Watanabe, T. Taniguchi, K. Haule and E.Y. Andrei, Nature, 573 (2019) 91.

https://www.nature.com/articles/s41586-019-1460-4

James Hone

Tunable electronic and optical properties in rotatable heterostructures

By. Dr. James Hone (Columbia University)

Thursday 9 July, 15:00 – 16:15 CEST

Link to join in: http://s.ic.fo/JamesHone090720

ABSTRACT

Department of Mechanical Engineering, Center for Precision Assembly of Superstratic and Superatomic Solids, Columbia University, New York 10027 USA

The weak bonding between layers in van der Waals heterostructures provides a new opportunity to create tunable structures. We rotate the top layer of a heterostructure using a contact-mode atomic force microscope (AFM) to modify the interfacial twist angle and moirè wavelength, modifying a number of emergent properties. In this talk I will describe three applications of this technique: (1) tuning bandstructure in graphene-hBN interfaces¹; (2) tuning symmetry in graphene with two hBN layers²; and tuning the nonlinear response of hBN-hBN interfaces³.

Ribeiro-Palau, R., C.J. Zhang, K. Watanabe, T. Taniguchi, J. Hone, and C.R. Dean, “Twistable electronics with dynamically rotatable heterostructures“, Science 361, 690 (2018).
Finney, N.R., M. Yankowitz, L. Muraleetharan, K. Watanabe, T. Taniguchi, C.R. Dean, and J. Hone, “Tunable crystal symmetry in graphene-boron nitride heterostructures with coexisting moire superlattices“, Nature Nanotechnology 14, 1029 (2019).

Kaiyuan Yao, Nathan R. Finney, Jin Zhang, Samuel L. Moore, Lede Xian, Nicolas Tancogne-Dejean, Fang Liu, Jenny Ardelean, Xinyi Xu, Dorri Halbertal, K. Watanabe, T. Taniguchi, Hector Ochoa, Ana Asenjo-Garcia, Xiaoyang Zhu, D. N. Basov, Angel Rubio, Cory R. Dean, James Hone, P. James Schuck, “Nonlinear twistoptics at symmetry-broken interfaces”, submitted

BIO

James Hone is currently Wang Fong-Jen Professor of Mechanical Engineering at Columbia University, and director of PAS³, Columbia’s Materials Science Research and Engineering Center (MRSEC). He received his BS in physics from Yale in 1990, and PhD in experimental condensed matter physics from UC Berkeley in 1998, and did postdoctoral work at the University of Pennsylvania and Caltech, where he was a Millikan Fellow. He joined the Columbia faculty in 2003.

Jeanie Lau

Flat Bands in Flatlands

By. Dr. Jeanie Lau (Ohio State University)

Wednesday 15 July, 16:30 – 17:45 CEST

Link to join in: http://s.ic.fo/JeanieLau150720

ABSTRACT

In a flat band system, the charge carriers’ energy-momentum relation is very weakly dispersive. The resultant large density of states and the dominance of Coulomb potential energy relative to the kinetic energy often favor the formation of strongly correlated electron states, such as ferromagnetism, nematicity, antiferromagnetism, superconductivity, and charge density waves. The advent of two-dimensional (2D) materials and their heterostructures has ushered in a new era for exploring, tuning and engineering of flat band system. Here I will present observation of correlated insulating and superconducting states in twisted bilayer graphene below the magic angle, and also discuss possible moiré systems other than those based on graphene or transition metal dichalcogenides.

BIO

Chun Ning (Jeanie) Lau is a Professor in the Department of Physics at The Ohio State University. She received her BA in physics from University of Chicago in 1994, and PhD in physics from Harvard in 2001. She was a research associate at Hewlett Packard Labs in Palo Alto from 2002 to 2004, before joining University of California, Riverside in 2004 as an assistant professor. She was promoted to associate professor in 2009 and full professor in 2012. Starting January 2017 she moved to The Ohio State University. The honors and awards she has received include the NSF CAREER award, the PECASE award and APS Fellow. Her research focuses on electronic, thermal and mechanical properties of nanoscale systems, in particular, graphene and other two-dimensional systems.

Jie Shan

Strong correlation physics in semiconductor moiré superlattices

By. Dr. Jie Shan (Cornell University)

Thursday 16 July, 16:30 – 17:45 CEST

Link to join in: http://s.ic.fo/JieShan160720

ABSTRACT

I will discuss a recent experimental realization of the two-dimensional (2D) triangular lattice Hubbard model in angle-aligned WSe₂/WS₂ bilayers, which form moiré superlattices because of the difference in lattice constant between the two semiconductors. The quantum phase diagram near the half filling of the first moiré miniband will be studied by probing both the charge and magnetic order of the system.

BIO

Jie Shan is a professor of applied & engineering physics and physics at Cornell University. She received her diploma in mathematics and physics from Moscow State University, Russia and Ph.D. in physics from Columbia University. Research in her group is focused on experimental studies of the electronic and optical properties of nanoscale materials. Current activities have involved the investigation of novel two-dimensional atomic crystals such as graphene and transition metal dichalcogenides.

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

https://www.nature.com/articles/s41586-020-2085-3

Leni Bascones

Interactions in magic-angle twisted bilayer graphene

By. Dr. Leni Bascones (ICMM Madrid)

Monday 13 July, 16:30 – 17:45 CEST

Link to join in: http://s.ic.fo/LeniBascones130720

ABSTRACT

Insulating and superconducting states appear upon doping magic angle twisted bilayer graphene, in which two graphene layers are rotated by a relative angle q~1°. The nature of these phases is not clear yet. The observed states depend on doping, on the proximity to metallic gates and on experimental details such as alignment to the substrate or strain, suggesting the competition of several phases. Moreover theoretical calculations have reported different ordered phases with very close ground state energies and the possible role played by Mott physics is still under debate. Understanding the role of the interaction processes is necessary to address the origin of the correlated states observed. In this talk I will discuss the different interaction energy scales which appear in the system and how they change as a function of the rotation angle and in the presence of screening due to nearby gates.

BIO

Tenured scientist at Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC).

I am interested in modelling the electronic properties of strongly correlated electron systems. After many years working on high-Tc superconductors, especially in the ones based on iron, at present I’m trying to understand the fascinating states of twisted bilayer graphene. Phd in Physics by Universidad Autónoma de Madrid, I did two postdoctoral stays at the University of Texas at Austin and at ETH-Zurich and several long research visits in France, Germany and USA. Co-editor of EPL. I am strongly involved in outreach activities on superconductivity and in the visibilization of women in science.

Marco Polini

Collective excitations in twisted bilayer graphene

By. Dr. Marco Polini (University of Pisa)

Friday 10 July, 16:30 – 17:45 CEST

Link to join in: http://s.ic.fo/MarcoPolini100720

ABSTRACT

Marco Polini^1,2,3

¹Dipartimento di Fisica dell’Università di Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy

²School of Physics & Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom

³Istituto Italiano di Tecnologia, Graphene Labs, Via Morego 30, I-16163 Genova, Italy

Several experimental probes have been used to explore the physics of twisted bilayer graphene (TBG), including electronic transport, quantum capacitance, and scanning tunneling spectroscopy. However, probes that access the response to finite in-plane momentum 𝑞 and frequency 𝜔 are expected to be rich sources of information in systems where electron-electron interactions play a dominant role. One of these probes is scattering near-field optical microscopy (SNOM), which enables the measurement of the dispersion relation of collective electronic excitations, such as Dirac plasmons in graphene. In this talk, I will discuss how SNOM can unveil the collective modes of electrons roaming in TBG [1] and present a theoretical approach [2] to calculate their spectra. I will try to argue that near-field optical probes offer new insights, complementary to those offered by other techniques, on the carrier dynamics in this correlated electron system.

Work supported by the European Union’s Horizon 2020 research and innovation programme under grant agreements No. 785219 “Graphene Core2” and No. 881603 “GrapheneCore3”.

[1] N. C.H. Hesp, I. Torre, D. Rodan-Legrain, P. Novelli, Y. Cao, S. Carr, S. Fang, P. Stepanov, D. Barcons-Ruiz, H. Herzig-Sheinfux, K. Watanabe, T. Taniguchi, D. K. Efetov, E. Kaxiras, P. Jarillo-Herrero, M. Polini, and F. H. L. Koppens, arXiv:1910.07893.

[2] P. Novelli, I. Torre, F. H. L. Koppens, F. Taddei, and M. Polini, arXiv:2005.09529.

BIO

Marco Polini graduated in Physics in 1999 from the University of Pisa (Italy) and received his Ph.D. in Physics in January 2003 from the Scuola Normale Superiore (Pisa, Italy). After his PhD he worked with Allan MacDonald at the University of Texas at Austin (USA) as a postdoctoral researcher and then returned to Pisa for a Researcher permanent position at the National Research Council (CNR). From September 2015 to December 2019 he held a Senior Scientist position at the Istituto Italiano di Tecnologia in Genoa (Italy), where he led the “Theory and technology of 2D materials” group. He is currently a Professor of Condensed Matter Physics at the Department of Physics of the University of Pisa (Italy) and a Professor of Physics at the School of Physics and Astronomy of the University of Manchester (UK). His recent interests include electron hydrodynamics, cavity QED of strongly correlated electron systems, topological and quantum plasmonics, and quantum effects in energy storage.

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

Optical and plasmonic properties of twisted bilayer graphene: Impact of interlayer tunneling asymmetry and ground-state charge inhomogeneity
Authors: Pietro Novelli, Iacopo Torre, Frank H. L. Koppens, Fabio Taddei, Marco Polini
https://arxiv.org/abs/2005.09529

Pablo Jarillo-Herrero

Competing orders and phase transition in magic-angle graphene

By. Dr. Pablo Jarillo-Herrero (MIT)

Friday 17 July, 15:00 – 16:15 CEST

Link to join in: http://s.ic.fo/PabloJarillo-Herrero170720

ABSTRACT

Strongly interacting electrons in solid-state systems often display tendency towards multiple broken symmetries in the ground state. The complex interplay between different order parameters can give rise to a rich phase diagram. Here, we report on the identification of intertwined phases with broken rotational symmetry in magic-angle twisted bilayer graphene (TBG). Using transverse resistance measurements, we find a strongly anisotropic phase located in a ‘wedge’ above the underdoped region of the superconducting dome. Upon crossing the superconducting dome, a reduction of the critical temperature is observed, similar to the behavior of certain cuprate superconductors. Furthermore, the superconducting state exhibits a anisotropic response to an directional-dependent in-plane magnetic field, revealing a nematic pairing state across the entire superconducting dome. These results indicate that nematic fluctuations might play an important role in the low-temperature phases of magic-angle TBG, and pave the way for using highly-tunable moiré superlattices to investigate intertwined phases in quantum materials.

BIO

Pablo Jarillo-Herrero is currently Cecil and Ida Green Professor of Physics at MIT. He received his “Licenciatura” in physics from the University of Valencia, Spain, in 1999. Then he spent two years at the University of California in San Diego, where he received a M.Sc. degree before going to the Delft University of Technology in The Netherlands, where he earned his Ph.D. in 2005. After a one-year postdoc in Delft, he moved to Columbia University, where he worked as a NanoResearch Initiative Fellow. He joined MIT as an assistant professor of physics in January 2008 and received tenure in 2015. He was promoted to Full Professor of Physics in 2018. Professor Jarillo-Herrero’s research interests lie in the area of experimental condensed matter physics, in particular quantum electronic transport and optoelectronics in novel two-dimensional materials, with special emphasis on investigating their superconducting, magnetic, and topological properties.

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

Nematicity and Competing Orders in Superconducting Magic-Angle Graphene
Yuan Cao, Daniel Rodan-Legrain, Jeong Min Park, Fanqi Noah Yuan, Kenji Watanabe, Takashi Taniguchi, Rafael M. Fernandes, Liang Fu, Pablo Jarillo-Herrero
https://arxiv.org/abs/2004.04148

Paco Guinea

Electronic structure and interactions in narrow bands in stacks of two dimensional materials.

By. Dr. Paco Guinea (IMDEA Madrid)

Tuesday 7 July, 16:30 – 17:45 CEST

Link to join in: http://s.ic.fo/PacoGuinea070720

ABSTRACT

The electronic structure, and the role of interactions is studied in stacks of graphene layers and other materials which show narrow electronic bands. Emphasis is made on:

The similarities and differences between the electronic structure of twisted bilayer graphene, and other stacks made from two dimensional materials which show narrow electronic bands.
The similarities and differences between the role of the electron-electron interaction in twisted bilayer graphene and other strongly correlated systems studied in condensed matter physics, such as the cuprate superconductors, heavy fermion systems, and others.

BIO

Education.

Ph. D. Universidad Autónoma de Madrid. 1980.

Sc. Universidad Complutense de Madrid. 1975.

Appointments.

2014- Senior researcher. IMDEA Nanoscience, Madrid (Spain).

2014-2019 Professor. University of Manchester, (UK).

2019- Senior researcher. Donostia International Physics Center (Spain).

1993-2014 Senior Researcher, CSIC (Spain).

1987-1993 Researcher, CSIC (Spain).

1984-1987 Assistant Professor (tenured), Universidad Autónoma de Madrid (Spain).

1982-1984 Fullbright Scholar, Institute for Theoretical Physics, University of California at

Santa Barbara (USA).

1980-1982 Assistant Professor (non tenured), Universidad Autónoma de Madrid (Spain).

1976-1980 Ph. D. student, CSIC (Spain).

Other positions.

2004-2005 Invited Scholar. Boston University (USA).

1997, Feb.-Aug. Invited Scholar, University of California at San Diego (USA).

1991-1992 Uhlenbeck Professor, University of Michigan at Ann Arbor (USA).

Research interests.

Francisco Guinea has made important contributions in topics such as macroscopic quantum mechanics, pattern formation, magnetism, and the theory of superconductivity and strongly correlated systems. In recent times he has been doing research in graphene and other two dimensional materials, where he is one of the leading theoreticians worldwide.

Many articles deal with problems at the interface between different areas, and they illustrate how concepts developed in a given subfield can be usefully applied to others.

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arXiv:2004.01577

Band structure and insulating states driven by the Coulomb interaction in twisted bilayer graphene, Tommaso Cea, Francisco Guinea

Rafael Fernandes

Electronic nematicity in moiré superlattices.

By. Dr. Rafael Fernandes (University of Minnesota)

Tuesday 14 July, 16:30 – 17:45 CEST

Link to join in: http://s.ic.fo/RafaelFernandez140720

ABSTRACT

In an electronic nematic phase, the rotational symmetry of the system is spontaneously broken not by lattice, but by electronic degrees of freedom, such as spin, orbital, or valley. In this talk, different theoretical models for the breaking of the three-fold rotational symmetry of the triangular moiré superlattice of twisted bilayer graphene in both the normal and superconducting states will be discussed and contrasted with recent experimental observations. Particular emphasis will be given to the coupling between the electronic nematic and the moiré elastic degrees of freedom, highlighting how nematicity in twisted two-dimensional materials is distinct than that realized in other quantum materials.

BIO

I received my PhD from the University of Campinas, Brazil, in 2008. Before becoming a professor at the University of Minnesota in 2012, I was a postdoc in the Ames Laboratory and a joint postdoc in Columbia University and in the Los Alamos National Lab. My main research activities are in theoretical condensed matter physics, particularly in strongly correlated systems. I am interested in clean and disordered systems in which the collective behaviour of the electrons gives rise to ordered states that break different symmetries of the system, such as superconductivity, magnetism, nematic ordering, and orbital ordering. My aim is to understand not only the impact of these individual phases on the electronic structure and macroscopic properties of the system, but also how they interact with each other.

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

Nematicity with a twist: rotational symmetry breaking in a moiré superlattice

https://arxiv.org/abs/1911.11367

Senthil Todadri

Topology and correlations in graphene Moiré lattices.

By. Dr. Senthil Todadri (MIT)

Wednesday 15 July, 15:00 – 16:15 CEST

Link to join in: http://s.ic.fo/SenthilTodadri150720

ABSTRACT

A number of nearly flat band graphene moire latttices hist bands that are topological. Due the near flatness of the dispersion, correlation effects become important. Thus theoretical modelling needs to deal with strong correlations in a partially filled topological band. In this talk I will describe the emergence of band topology in moire graphene some simple examples, and present some simple results on the efects of correlations. I will make contact with recent experiments observing the quantum anomalous Hall effect in Moiré graphene.

BIO

Senthil is a Professor of Physics at the Massachusetts Institute of Technology (MIT), USA. He joined MIT in January 2001 as an Assistant Professor of Physics. Before that, he was a postdoctoral fellow at the Kavli Institute for Theoretical Physics in Santa Barbara, CA. His graduate degree is from Yale University, and his undergraduate degree is from the Indian Institute of Technology, Kanpur. He is broadly interested in the theory of quantum many body systems with a focus on novel phases and phase transitions that challenge our current paradigms.

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

Some of what I say will build on arguments in

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.205150

https://arxiv.org/abs/1911.11367

Tobias Roedel

Q&A with a Nature editor

By. Dr. Tobias Roedel (Nature Editor)

Friday 10 July, 18:00 – 19:00 CEST

Link to join in: http://s.ic.fo/Nature100720

ABSTRACT

Scientific publishing is an integral part of the scientific endeavor. The number of publications has increased steadily over the last years due to a metrics-driven ‘publish-or-perish’ culture and an increase in research funding in certain countries. At Nature, we strive to filter only the most significant advances and to communicate their impact to a broad audience – beyond the specialized community. Our assessment of significance is based on objective criteria, but our final decisions are not devoid of subjectivity. As our editorial decision can be controversial, I am happy to answer your questions about the editorial process behind these decisions. Also, feel free to ask questions related to the job of an editor or to scientific publishing more generally.

BIO

Born in a small village in Northern Bavaria, Germany, Dr. Tobias Rödel received his M.Sc. at the University of Würzburg and his PhD at the University Paris-Saclay. His research during the PhD was focused on the characterization of the band structure of 2D electronic states at the surface of transition metal oxides. A short postdoc at the University of Luxembourg was based on the growth and characterization of thin film chalcogenides for photovoltaic and detector applications. Since 2018, he works as an editor at the scientific journal ‘Nature’ handling manuscripts on condensed matter physics including moiré materials.

Tobias Stauber

Superconductivity and chirality in twisted bilayer graphene

By. Dr. Tobias Stauber (Instituto de Ciencia de Materiales de Madrid, CSIC)

Thursday 16 July, 15:00 – 16:15 CEST

Link to join in: http://s.ic.fo/TobiasStauber160720

ABSTRACT

Twisted bilayer graphene has attracted much attention due to its novel electronic and optical properties. After a brief introduction, I will present our recent theoretical results on the superconducting instability and also on the inherent chirality of the system. In particular, I will argue that an extended van Hove singularity can give rise to Kohn-Luttinger superconductivity and strange metal behavior [1,2]. I further show that the Moiré structure of TBG leads to a paramagnetic response and chiral plasmons which are accommodated by a longitudinal magnetic moment [3]. This unusual response also leads to an emergent magnetic texture when the system is driven out-of-equilibrium [4].

[1] J. Gónzalez and T. Stauber: Kohn-Luttinger superconductivity in twisted bilayer graphene. Phys. Rev. Lett. 122, 026801 (2019)

[2] J. Gónzalez and T. Stauber: Marginal Fermi liquid in twisted bilayer graphene. Phys. Rev. Lett. 124, 186801 (2020)

[3] T. Stauber, T. Low, and G. Gómez-Santos: Chiral response in twisted bilayer graphene. Phys. Rev. Lett. 120, 046801 (2018)

[4] D. A. Bahamon, G. Gómez-Santos, and T. Stauber: Emergent magnetic texture in driven twisted bilayer graphene. Nanoscale (in press).

BIO

Tobias Stauber is a Tenured Scientist at the Instituto de Ciencia de Materiales (ICMM, CSIC) in Madrid. He obtained his PhD in Theoretical Physics from the University of Heidelberg, Germany in 2002 on “Flow Equations for Hamiltonians”. He then continued with his postdoctorial studies at the ICMM, CSIC, Spain with studies on graphene. He later was Assistant Research Professor at the University of Minho, Portugal and at the University Autónoma of Madrid, Spain. Since 2014, he is a tenured scientist at the Material Science Institute of Madrid (ICMM) of the Spanish National Research Council (CSIC). His research focus is on the electric and optical response of graphene and related two-dimensional materials.

Xavier Marie

Excitons in Transition Metal Dichalcogenide Mono- and Bi-layers

By. Dr. Xavier Marie (INSA Toulouse)

Tuesday 7 July, 15:00 – 16:15 CEST

Link to join in: http://s.ic.fo/XavierMarie070720

ABSTRACT

Université de Toulouse, INSA-CNRS-UPS, Laboratoire de Physique et Chimie des Nano-Objets,

135 Avenue de Rangueil, 31077 Toulouse, France

In this talk I will give an overview of the properties of 2D excitons in Transition Metal Dichalcogenides : giant binding energy, oscillator strength, exchange interactions, spin/valley…
Then I will present recent optical spectroscopy experiments on the control of interlayer excitons in MoS2 bilayers. We show that there is a correlation between the stacking order and the interlayer coupling of valence states in both as-grown MoS2 homobilayer samples and in artificially stacked bilayers from monolayers. Finally we have evidenced the giant Stark splitting of the interlayer excitons characterized by a large oscillator strength in bilayer MoS2.

BIO

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

He has worked for about 30 years on electronic and optical properties of low dimensional semiconductor structures (quantum wells, quantum dots, 2D materials). His main present interest is the optical, valley and spin coherence in semiconductor nanostructures and band structure engineering of semiconductors for optical telecommunication devices and solar cells.

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER:

“Colloquium: Excitons in atomically thin transition metal dichalcogenides”RMP 90, 021001 (2018) and “Giant Stark splitting of an exciton in bilayer MoS2” arXiv:2002.02507 (Nature Nano in press)

https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.90.021001

https://arxiv.org/abs/2002.02507

Organisation

The Local Organising Committee is Dima Efetov (ICFO), Pablo Jarillo-Herrero (MIT), Frank Koppens (ICFO), Adrian Bachtold (ICFO), Maciej Lewenstein (ICFO), Antoine Reserbat-Plantey (ICFO), and Dr Robert Sewell (ICFO).

ICFO – the Institute of Photonic Sciences, is a young research institution that aims to advance the very limits of the science and technology of light, tackling important challenges faced by society at large in all areas of life, including health, energy, information, safety, security and caring for the environment. ICFO is a member of BIST, the Barcelona Institute of Science and Technology. More information about ICFO can be found HERE.

This project has been co-funded with 50% by the European Regional Development Fund under the framework of the ERFD Operative Programme for Catalunya 2014-2020 (project GraphCAT, ref. 001-P-2001702).

ICFO – MIT Schools on the Frontiers of Light aim at giving talented young researchers and students worldwide a first introduction to a thematic research area and a taste of an international research environment. These schools incorporate a dynamic and social learning environment beyond participating in lectures, including group discussions, direct interactions with the lecturers, student talks and poster presentations.

ICFO does not tolerate any type of conduct or behavior considered harassment or bullying and has a clear defined policy against harassment.

ICFO-MIT School on the Frontiers of Light

ONLINE SYMPOSIUM ON “EMERGENT PHENOMENA IN MOIRE MATERIALS”

Overview

¡NEW! SPIE@ICFO CHAIR RESEARCH FELLOWSHIPS

REGISTRATION FOR ICFO-MIT SCHOOLS ON THE FRONTIERS OF LIGHT

Program

THE SEMINAR VIDEOS NOW ARE AVAILABLE ONLINE

Abstracts

Moiré Magic

By Dr. Allan H. MacDonald (Texas University)

Monday, July 6th 15:00 – 16:15 CEST​

Link to join in: http://s.ic.fo/AllanMacDonald060720

ABSTRACT

BIO

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER: ​

Monday, July 6th 15:00 – 16:15 CEST

>> PREPARE FOR THE SEMINAR! WE RECOMMEND YOU TO READ THIS PAPER: