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Isospin magnetism and spin-polarized superconductivity in Bernal bilayer graphene

Zhou, Haoxin and Holleis, Ludwig and Saito, Yu and Cohen, Liam and Huynh, William and Patterson, Caitlin L. and Yang, Fangyuan and Taniguchi, Takashi and Watanabe, Kenji and Young, Andrea F. (2022) Isospin magnetism and spin-polarized superconductivity in Bernal bilayer graphene. Science, 375 (6582). pp. 774-778. ISSN 0036-8075. doi:10.1126/science.abm8386. https://resolver.caltech.edu/CaltechAUTHORS:20220324-224396500

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Abstract

In conventional superconductors, Cooper pairing occurs between electrons of opposite spin. We observe spin-polarized superconductivity in Bernal bilayer graphene when doped to a saddle-point van Hove singularity generated by a large applied perpendicular electric field. We observe a cascade of electrostatic gate-tuned transitions between electronic phases distinguished by their polarization within the isospin space defined by the combination of the spin and momentum-space valley degrees of freedom. Although all of these phases are metallic at zero magnetic field, we observe a transition to a superconducting state at finite magnetic field B_‖ ≈ 150 milliteslas applied parallel to the two-dimensional sheet. Superconductivity occurs near a symmetry-breaking transition and exists exclusively above the B_‖ limit expected of a paramagnetic superconductor with the observed transition critical temperature T_C ≈ 30 millikelvins, consistent with a spin-triplet order parameter.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1126/science.abm8386DOIArticle
https://doi.org/10.25349/D9G892DOIData
ORCID:
AuthorORCID
Zhou, Haoxin0000-0003-1235-0035
Holleis, Ludwig0000-0001-9718-2477
Saito, Yu0000-0001-6155-5278
Cohen, Liam0000-0002-7257-4105
Yang, Fangyuan0000-0001-8418-7383
Taniguchi, Takashi0000-0002-1467-3105
Watanabe, Kenji0000-0003-3701-8119
Young, Andrea F.0000-0001-5954-8028
Additional Information:© 2022 American Association for the Advancement of Science. Received 18 October 2021; accepted 4 January 2022. Published online 13 January 2022. The authors acknowledge discussions with E. Berg, S. Das Sarma, Y.-Z. Chou, A. Ghazaryan, L. Levitov, A. Macdonald, M. Serbyn, C. Varma, and M. Zaletel. This project was primarily funded by the Department of Energy under DE-SC0020043. Support to purchase the cryogen-free dilution refrigerator was provided by the Army Research Office under award W911NF-17-1-0323. A.F.Y. acknowledges the support of the Gordon and Betty Moore Foundation under award GBMF9471 and the Packard Foundation under award 2016-65145 for general group activities. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan (grant no. JPMXP0112101001), and JSPS KAKENHI (grant nos. 19H05790, 20H00354, and 21H05233). Author contributions: H.Z. and L.H. fabricated the devices. H.Z., L.H., Y.S., W.H., C.L.P., and F.Y. performed the measurements. H.Z., L.H., Y.S., W.H., C.L.P., F.Y., and A.F.Y. analyzed the data. L.C. assembled the cryogenic instrumentation. T.T. and K.W. grew the hexagonal boron nitride crystals. H.Z. and A.F.Y. conceived the experiment and wrote the paper. The authors declare no competing interests. Data and materials availability: All data shown in the main text and the supplementary materials are available in the Dryad data repository (49).
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0020043
Army Research Office (ARO)W911NF-17-1-0323
Gordon and Betty Moore FoundationGBMF9471
David and Lucile Packard Foundation2016-65145
Ministry of Education, Culture, Sports, Science and Technology (MEXT)JPMXP0112101001
Japan Society for the Promotion of Science (JSPS)19H0579
Japan Society for the Promotion of Science (JSPS)20H00354
Japan Society for the Promotion of Science (JSPS)21H05233
Issue or Number:6582
DOI:10.1126/science.abm8386
Record Number:CaltechAUTHORS:20220324-224396500
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20220324-224396500
Official Citation:Isospin magnetism and spin-polarized superconductivity in Bernal bilayer graphene. Haoxin Zhou, Ludwig Holleis, Yu Saito, Liam Cohen, William Huynh, Caitlin L. Patterson, Fangyuan Yang, Takashi Taniguchi, Kenji Watanabe, Andrea F. Young Science, 375 (6582); DOI: 10.1126/science.abm8386
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114067
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:24 Mar 2022 22:14
Last Modified:24 Mar 2022 22:14

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