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Spectroscopic Signatures of Strong Correlations and Unconventional Superconductivity in Twisted Trilayer Graphene

Kim, Hyunjin and Choi, Youngjoon and Lewandowski, Cyprian and Thomson, Alex and Zhang, Yiran and Polski, Robert and Watanabe, Kenji and Taniguchi, Takashi and Alicea, Jason and Nadj-Perge, Stevan (2021) Spectroscopic Signatures of Strong Correlations and Unconventional Superconductivity in Twisted Trilayer Graphene. . (Unpublished)

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Magic-angle twisted trilayer graphene (MATTG) has emerged as a novel moiré material that exhibits both strong electronic correlations and unconventional superconductivity. However, spectroscopic studies of its electronic properties are lacking, and the nature of superconductivity and the corresponding order parameter in this system remain elusive. Here we perform high-resolution scanning tunneling microscopy and spectroscopy of MATTG and reveal extensive regions of atomic reconstruction that favor mirror-symmetric stacking. In these regions, we observe a cascade of symmetry-breaking electronic transitions and doping-dependent band structure deformations similar to those realized in magic-angle bilayers, as expected theoretically given the commonality of flat bands. More strikingly, in a density window spanning two to three holes per moire unit cell, spectroscopic signatures of superconductivity are manifest as pronounced dips in the tunneling conductance at the Fermi level accompanied by coherence peaks that become gradually suppressed at elevated temperatures and magnetic fields. The observed evolution of the conductance with doping is consistent with a gate-tunable transition from a gapped to a nodal superconductor, which we show theoretically is compatible with a sharp transition from a Bardeen-Cooper-Schrieffer (BCS) to a Bose-Einstein condensation (BEC) superconductor with a nodal order parameter. Within this doping window, we also detect peak-dip-hump structures suggesting that superconductivity is driven by strong coupling to bosonic modes of MATTG. Our results pave the way for further understanding of superconductivity and correlated states in graphene-based moiré structures beyond twisted bilayers, where unconventional superconductivity and nodal pairing were reported.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Kim, Hyunjin0000-0001-9886-0487
Lewandowski, Cyprian0000-0002-6944-9805
Thomson, Alex0000-0002-9938-5048
Zhang, Yiran0000-0002-8477-0074
Polski, Robert0000-0003-0887-8099
Watanabe, Kenji0000-0003-3701-8119
Taniguchi, Takashi0000-0002-1467-3105
Alicea, Jason0000-0001-9979-3423
Nadj-Perge, Stevan0000-0002-2916-360X
Additional Information:Attribution 4.0 International (CC BY 4.0). We acknowledge discussions with Felix von Oppen, Gil Refael, Yang Peng, and Ali Yazdani. This work has been primarily supported by Office of Naval Research (grant no. N142112635); National Science Foundation (grant no. DMR-2005129); and Army Research Office under Grant Award W911NF17-1-0323. Nanofabrication efforts have been in part supported by Department of Energy DOE-QIS program (DE-SC0019166). S.N-P. acknowledges support from the Sloan Foundation. J.A. and S.N.-P. also acknowledge support of the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation through Grant GBMF1250; C.L. acknowledges support from the Gordon and Betty Moore Foundation’s EPiQS Initiative, Grant GBMF8682. A.T. and J.A. are grateful for the support of the Walter Burke Institute for Theoretical Physics at Caltech. H.K. and Y.C. acknowledge support from the Kwanjeong fellowship. Author Contribution: H.K. and Y.C. fabricated samples with the help of Y.Z. and R.P., and performed STM measurements. H.K., Y.C., and S.N.-P. analyzed the data. C.L. and A.T. provided the theoretical analysis supervised by J.A. S.N.-P. supervised the project. H.K., Y.C., C.L., A.T., J.A., and S.N.-P. wrote the manuscript with input from other authors. Data availability: The data that support the findings of this study are available from the corresponding authors on reasonable request.
Group:Institute for Quantum Information and Matter, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Office of Naval Research (ONR)N142112635
Army Research Office (ARO)W911NF17-1-0323
Department of Energy (DOE)DE-SC0019166
Alfred P. Sloan FoundationUNSPECIFIED
Institute for Quantum Information and Matter (IQIM)UNSPECIFIED
Gordon and Betty Moore FoundationGBMF1250
Gordon and Betty Moore FoundationGBMF8682
Walter Burke Institute for Theoretical Physics, CaltechUNSPECIFIED
Kwanjeong Educational FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20220113-182215445
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112870
Deposited By: George Porter
Deposited On:13 Jan 2022 21:23
Last Modified:13 Jan 2022 21:23

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