TY - JOUR
T1 - Tuning interactions between spins in a superconductor
AU - Ding, Hao
AU - Hu, Yuwen
AU - Randeria, Mallika T.
AU - Hoffman, Silas
AU - Deb, Oindrila
AU - Klinovaja, Jelena
AU - Loss, Daniel
AU - Yazdani, Ali
N1 - Funding Information:
ACKNOWLEDGMENTS. We acknowledge discussions with Y. Meir. This work has been primarily supported by the Gordon and Betty Moore Foundation as part of the Emergent Phenomena in Quantum Systems initiative (Grants GBMF4530 and GBMF9469), Office of Naval Research Grants N00014-17-1-2784 and N00014-14-1-0330, NSF Materials Research Science and Engineering Centers programs through Princeton Center for Complex Materials Grants DMR-142054 and NSF-DMR-2011750, as well as NSF-DMR-1608848 and NSF-DMR-1904442. This work was also supported by the Swiss National Science Foundation and the National Centre of Competence in Research Quantum Science and Technology (J.K., O.D., S.H., and D.L.) and the European Union’s Horizon 2020 Research and Innovation Program (European Research Council Starting Grant; Grant Agreement 757725 to J.K.). A.Y. acknowledges the hospitality of the Trinity College and Cavendish Laboratory in Cambridge, UK, during the preparation of this manuscript, which was also funded in part by a Quantum Emergence Exchange grant from the Institute for Complex Adaptive Matter and the Gordon and Betty Moore Foundation (Grant GBMF5305).
Publisher Copyright:
© 2021 National Academy of Sciences. All rights reserved.
PY - 2021/4/6
Y1 - 2021/4/6
N2 - Novel many-body and topological electronic phases can be created in assemblies of interacting spins coupled to a superconductor, such as one-dimensional topological superconductors with Majorana zero modes (MZMs) at their ends. Understanding and controlling interactions between spins and the emergent band structure of the in-gap Yu-Shiba-Rusinov (YSR) states they induce in a superconductor are fundamental for engineering such phases. Here, by precisely positioning magnetic adatoms with a scanning tunneling microscope (STM), we demonstrate both the tunability of exchange interaction between spins and precise control of the hybridization of YSR states they induce on the surface of a bismuth (Bi) thin film that is made superconducting with the proximity effect. In this platform, depending on the separation of spins, the interplay among Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, spin-orbit coupling, and surface magnetic anisotropy stabilizes different types of spin alignments. Using high-resolution STM spectroscopy at millikelvin temperatures, we probe these spin alignments through monitoring the spin-induced YSR states and their energy splitting. Such measurements also reveal a quantum phase transition between the ground states with different electron number parity for a pair of spins in a superconductor tuned by their separation. Experiments on larger assemblies show that spin-spin interactions can be mediated in a superconductor over long distances. Our results show that controlling hybridization of the YSR states in this platform provides the possibility of engineering the band structure of such states for creating topological phases.
AB - Novel many-body and topological electronic phases can be created in assemblies of interacting spins coupled to a superconductor, such as one-dimensional topological superconductors with Majorana zero modes (MZMs) at their ends. Understanding and controlling interactions between spins and the emergent band structure of the in-gap Yu-Shiba-Rusinov (YSR) states they induce in a superconductor are fundamental for engineering such phases. Here, by precisely positioning magnetic adatoms with a scanning tunneling microscope (STM), we demonstrate both the tunability of exchange interaction between spins and precise control of the hybridization of YSR states they induce on the surface of a bismuth (Bi) thin film that is made superconducting with the proximity effect. In this platform, depending on the separation of spins, the interplay among Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, spin-orbit coupling, and surface magnetic anisotropy stabilizes different types of spin alignments. Using high-resolution STM spectroscopy at millikelvin temperatures, we probe these spin alignments through monitoring the spin-induced YSR states and their energy splitting. Such measurements also reveal a quantum phase transition between the ground states with different electron number parity for a pair of spins in a superconductor tuned by their separation. Experiments on larger assemblies show that spin-spin interactions can be mediated in a superconductor over long distances. Our results show that controlling hybridization of the YSR states in this platform provides the possibility of engineering the band structure of such states for creating topological phases.
KW - Condensed matter physics
KW - Majorana fermions
KW - Scanning tunneling microscopy
KW - Superconductivity
KW - Topological states
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U2 - 10.1073/pnas.2024837118
DO - 10.1073/pnas.2024837118
M3 - Article
C2 - 33782131
AN - SCOPUS:85103745534
SN - 0027-8424
VL - 118
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 14
M1 - e2024837118
ER -