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Flat Band Moirés European Physical Society Condensed Matter Division Flat Band Moirés Leni Bascones1, Dmitri Efetov2, Johannes Lischner3 1 Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC 2 Institute of Photonic Sciences ICFO 3 Imperial College London Wednesday, September, 2nd 9:30-10:10 Correlated, insulating and superconducting States in twisted bilayer graphene Below the Magic Angle. Jeanie Lau (invited). 10:10-10:30 Flat band superconductivity in twisted bilayer graphene. Tero Heikkilä, T. Peltonen, A. Julku, R. Ojajärvi, L. Long, P. Törmä. 10:30-10:50 Band structure and insulating states driven by the Coulomb interactions in twisted bilayer graphene. Tommaso Cea, F. Guinea. 10:50-11:10 Interactions in magic-angle twisted bilayer graphene. María José Calderón, E. Bascones. 11:10-11:30 Evidence of weakly dispersive bands in twisted bilayer graphene from nano-ARPES. Simone Lisi, X. Lu, T. Benschop, T. A. de Jong, P. Stepanov, J. R. Duran, Fl. Margot, I. Cucchi, E. Cappelli, A. Hunter, A. Tamai, V. Kandyba, A. Giampietri, A. Barinov, Johannes Jobst, Vincent Stalman, M. Leeuwenhoek, K. Watanabe, T. Taniguchi, L. Rademaker, S. J. van der Molen, M. Allan, D. K. Efetov, F. Baumberger. 11:30-11:50 Marginal Fermi liquid in twisted bilayer graphene José González, T. Stauber. 11:50-12:10 Inconmensurability induced sub-ballistic states in twisted bilayer graphene. Miguel de Jesús Mestre Gonçalves, H. Z. Olyaei1, B. Amorim, R. Mondaini, P. Ribeiro, E. V. Castro. 12:10-12:30 Strain induced excitonic instability in twisted bilayer graphene. Héctor Ochoa. Thursday, September 3rd 9:30-10:10 Moiré physics and symmetry breaking in magnetically encapsulated van der Waals structures. José Lado (invited). 10:10-10:30 Twist angle homogeneity in twisted bilayer graphene devices studied with STM. Tjerk Benschop, T. A. de Jong, V. Stalman, M. Leeuwenhoek, P. Stepanov, X. Lu, S. J. van der Molen, D. K. Efetov, M. P. Allan. CMD2020GEFES European Physical Society Condensed Matter Division 10:30-10:50 Chirality in twisted bilayer graphene. Tobias Stauber, J. González, G. Gómez-Santos. 10:50-11:10 Topological excitons and bosonic fractional quantum Hall liquids in twisted bilayer graphene. Yves Kwan, Y. Hu, S. H. Simon, and S. A. Parameswaran. 11:10-11:30 Topological flat bands and correlated states in twisted monolayer-bilayer graphene. Louk Rademaker, I. Protopopov, D. Abanin . 11:30-11:50 Double superlattices and supercurrent measurements in graphene/hBN superlattices. Peter Makk, D. Indolese, L. Wang, S. Zihlmann, R. Delangrange, A. Baumgartner and Ch. Schönenberger. 11:50-12:10 Atomic scale structure and broken symmetries in twisted double bilayer graphene. Carmen Rubio Verdú, S. Turkel, L. Song, L. Klebl, D. M. Kennes, L. Xian, H. Ochoa, K. Watanabe, T. Taniguchi, Á. Rubio, A. N. Pasupathy. 12:10-12:30 Floquet engineering of twisted double bilayer graphene. Martín Rodríguez Vega, M. Vogl, G.A. Fiete. Friday, September 4th 9:30-10:10 Correlated electrons in a moiré superlattice probed with optical spectroscopy. Yuya Shimazaki (invited), I. Schwartz, K. Watanabe, T. Taniguchi, M. Kroner, A. Imamoglu. 10:10-10:30 Flatbands in twisted transition metal dichalcogenides. José Ángel Silva Guillén, Z. Zhan, Y. Zhang, G. Yu, F. Guinea, S. Yuan. 10:30-10:50 Flatbands in transition metal dichalcogenides –when and why do we have them. Priya Mahadevan, S. Patra, P. Kumari. 10:50-11:10 Twisted nano-optics: Manipulating light at the Nanoscale with Twisted Polaritonics Slabs. Jiahua Duan, N. Capote-Robayna, J. Taboada-Gutiérrez, G. Álvarez-Pérez, I. Prieto, J. Martín- Sánchez, A. Y. Nikitin, P. Alonso-González. 11:10-11:30 Simulating twistronics with ultra-cold atoms. Alejandro González Tudela, J.I. Cirac. 11:30-11:50 Dirac node engineering and flat bands in doped Dirac materials. Anna Pertsova, S P. Johnson, D. Arovas, A. V. Balatsky. 11:50-12:10 Domain walls in twisted bilayer graphene. Glenn Wagner, Y. Kwan, N. Chakraborty, S. Simon, S. Parameswaran 12:10-12:30 Deconfinement of Mott Localized Electrons into Topological and Spin-Orbit Coupled Dirac Fermions. José Pizarro, S. Adler, K. Zantout, T. Mertz, P. Barone, R. Valenti, G. Sangiovanni, T.O. Wehling. CMD2020GEFES European Physical Society Condensed Matter Division Posters 1. Electronic compressibility of Magic Angle Twisted Bilayer Graphene. Alejandro Jimeno, F. Guinea. 2. Normal and Andreev transport in Magic Angle Graphene Junctions. Miguel Alvarado Herrero, A. Levy-Yeyati. 3. Valley spirals in magnetically encapsulated twisted bilayer graphene. Tobías Wolf, O. Zilberberg, G. Blatter, J. L. Lado. 4. Conductivity of twisted bilayer graphene nanotubes with disorder. Héctor Sainz Cruz, T. Cea, F. Guinea. 5. Spin polarization in Twisted Transition Metal Dichalcogenides. Ignacio Vicent, J. A. Silva- Guillén, F. Guinea. CMD2020GEFES Correlated Insulating and Superconducting States in Twisted Bilayer Graphene Below the Magic Angle Jeanie Lau The Ohio State University The emergence of flat bands and correlated behaviors in “magic angle” twisted bilayer graphene (tBLG) has sparked tremendous interest. Here we report observation of both superconductivity and the Mott-like insulating state in a tBLG device with a twist angle of ~0.93º, which is smaller than the magic angle by 15%. At an electron concentration of ±5 electrons/moiré unit cell, we observe a narrow resistance peak with an activation energy gap ~0.1 meV, indicating the existence of an additional correlated insulating state. This is consistent with theory predicting the presence of a high-energy band with an energetically flat dispersion. At a doping of ±12 electrons/moiré unit cell we observe a resistance peak due to the presence of Dirac points in the spectrum. Our results reveal that the "magic" range of tBLG is in fact larger than what is previously expected, and provide a wealth of new information to help decipher the strongly correlated phenomena observed in tBLG. European Physical Society Condensed Matter Division Flat band superconductivity in twisted bilayer graphene Tero Heikkilä1, Teemu Peltonen1, Aleksi Julku2, Risto Ojajärvi1, Liang Long2, ja Päivi Törmä2 1 University of Jyväskylä Department of Physics and Nanoscience Center, P.O. Box 35, 40600-University of Jyväskylä, Finland 2 Department of Applied Physics, Aalto University, P.O.Box 15100, 00076 Aalto, Finland [email protected] We present a microscopic mean-field theory [1,2] for the superconducting state of twisted bilayer graphene (TBG), where the electronic flat band emerging around the “magic twist angle” promotes superconductivity in a way that even conventional electron-phonon mechanism may be responsible for it. In this case the traditional MacMillan formula valid for systems with a clear Fermi surface fails to estimate the critical temperature, but has to be replaced by another one taking into account the full flat band [3]. We also show that even though the Fermi velocity vanishes for flat bands, TBG can exhibit a non- vanishing supercurrent and thereby a finite Berezinskii-Kosterlitz-Thouless temperature. The origin of this supercurrent in this case is in the quantum metric of the topological TBG bands [4]. Our model predicts and describes some relevant properties of TBG superconductivity, such as a strongly position dependent order parameter, precise angle dependent critical temperature, and a possibly anisotropic superfluid weight, depending on the pairing model. References (use bold Times New Roman 11) [1] T. J. Peltonen, R. Ojajärvi, and T. T. Heikkilä, Phys. Rev. B 98, 220504 (2018). [2] A. Julku, T. J. Peltonen, L. Liang, T. T. Heikkilä, and P. Törmä, Phys. Rev. B 101, 060505 (2020) [3] R. Ojajärvi, T. Hyart, M. A. Silaev, and T. T. Heikkilä, Phys. Rev. B 98, 054515 (2018). [4] S. Peotta and P. Törmä, Nat. Commun. 6, 8944 (2015). Fig. 1: (a) Bilayer graphene twisted to an angle θ. (b) Position dependent order parameter of the superconducting state. CMD2020GEFES European Physical Society Condensed Matter Division ! ! Band structure and insulating states driven by the Coulomb interaction in twisted bilayer graphene Tommaso Cea1, Francisco Guinea1,2 1 Imdea Nanoscience, Faraday 9, 28015 Madrid, Spain 2Donostia International Physics Center, Paseo Manuel de Lardiza ́bal 4, 20018 San Sebasti ́an, Spain [email protected] We analyze the phase diagram of twisted graphene bilayers near a magic angle. We consider the effect of the long range Coulomb interaction, treated within the self consistent Hartree-Fock approximation, and we study arbitrary band fillings. We find a rich phase diagram, with different broken symmetry phases, although tehy do not show necessarily a gap at the Fermi energy. There are non trivial effects of the electrostatic potential on the shape and the gaps of the bands in the broken symmetry phases. The results suggest that the non superconducting broken symmetry phases observed experimentally are induced by the long range exchange interaction. CMD2020GEFES European Physical Society Condensed Matter Division Interactions in magic-angle twisted bilayer graphene María J. Calderón1 and Leni Bascones1 1 Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC (Spain) [email protected] Insulating and superconducting states appear upon doping magic angle twisted bilayer graphene, in which two graphene layers are rotated by a relative angle ~1 [1-4]. 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 [5- 9] 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.
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