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  Magic Angle Spectroscopy

Kerelsky, A., McGilly, L., Kennes, D. M., Xian, L. D., Yankowitz, M., Chen, S., et al. (2018). Magic Angle Spectroscopy.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0003-A00D-A Version Permalink: http://hdl.handle.net/21.11116/0000-0003-A35A-0
Genre: Paper

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1812.08776.pdf (Preprint), 6MB
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2018
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https://arxiv.org/abs/1812.08776 (Preprint)
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 Creators:
Kerelsky, A.1, Author
McGilly, L.1, Author
Kennes, D. M.2, Author
Xian, L. D.3, Author              
Yankowitz, M.1, Author
Chen, S.1, 4, Author
Watanabe, K.5, Author
Taniguchi, T.5, Author
Hone, J.6, Author
Dean, C.1, Author
Rubio, A.3, 7, Author              
Pasupathy, A. N.1, Author
Affiliations:
1Department of Physics, Columbia University, New York, ou_persistent22              
2Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, ou_persistent22              
3Theory Group, Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society, ou_2266715              
4Department of Applied Physics and Applied Mathematics, Columbia University, New York, ou_persistent22              
5National Institute for Materials Science, ou_persistent22              
6Department of Mechanical Engineering, Columbia University, New York, ou_persistent22              
7Center for Computational Quantum Physics (CCQ), The Flatiron Institute, ou_persistent22              

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 Abstract: The electronic properties of heterostructures of atomically-thin van der Waals (vdW) crystals can be modified substantially by Moiré superlattice potentials arising from an interlayer twist between crystals. Moiré-tuning of the band structure has led to the recent discovery of superconductivity and correlated insulating phases in twisted bilayer graphene (TBLG) near the so-called "magic angle" of ∼1.1°, with a phase diagram reminiscent of high Tc superconductors. However, lack of detailed understanding of the electronic spectrum and the atomic-scale influence of the Moiré pattern has so far precluded a coherent theoretical understanding of the correlated states. Here, we directly map the atomic-scale structural and electronic properties of TBLG near the magic angle using scanning tunneling microscopy and spectroscopy (STM/STS). We observe two distinct van Hove singularities (vHs) in the LDOS which decrease in separation monotonically through 1.1° with the bandwidth (t) of each vHs minimized near the magic angle. When doped near half Moiré band filling, the conduction vHs shifts to the Fermi level and an additional correlation-induced gap splits the vHs with a maximum size of 7.5 meV. We also find that three-fold (C3) rotational symmetry of the LDOS is broken in doped TBLG with a maximum symmetry breaking observed for states near the Fermi level, suggestive of nematic electronic interactions. The main features of our doping and angle dependent spectroscopy are captured by a tight-binding model with on-site (U) and nearest neighbor Coulomb interactions. We find that the ratio U/t is of order unity, indicating that electron correlations are significant in magic angle TBLG. Rather than a simple maximization of the DOS, superconductivity arises in TBLG at angles where the ratio U/t is largest, suggesting a pairing mechanism based on electron-electron interactions.

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Language(s): eng - English
 Dates: 2018-12-20
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Method: No review
 Identifiers: arXiv: 1812.08776
 Degree: -

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