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Charge transfer excitations, pair density waves, and superconductivity in moiré materials

Slagle, Kevin and Fu, Liang (2020) Charge transfer excitations, pair density waves, and superconductivity in moiré materials. Physical Review B, 102 (23). Art. No. 235423. ISSN 2469-9950. doi:10.1103/PhysRevB.102.235423.

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Transition-metal dichalcogenide (TMD) bilayers are a new class of tunable moiré systems attracting interest as quantum simulators of strongly interacting electrons in two dimensions. In particular, recent theory predicts that the correlated insulator observed in WSe₂/WS₂ at half filling is a charge-transfer insulator similar to cuprates and, upon further hole doping, exhibits a transfer of charge from anionlike to cationlike orbitals at different locations in the moiré unit cell. In this work, we demonstrate that in this doped charge-transfer insulator, tightly bound charge-2e excitations can form to lower the total electrostatic repulsion. This composite excitation, which we dub a trimer, consists of a pair of holes bound to a charge-transfer exciton. When the bandwidth of doped holes is small, trimers crystallize into insulating pair density waves at a sequence of commensurate doping levels. When the bandwidth becomes comparable to the pair binding energy, itinerant holes and charge-2e trimers interact resonantly, leading to unconventional superconductivity similar to superfluidity in an ultracold Fermi gas near Feshbach resonance. Our theory is broadly applicable to strongly interacting charge-transfer insulators, such as WSe₂/WS₂ or TMD homobilayers under an applied electric field.

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Slagle, Kevin0000-0002-8036-3447
Additional Information:© 2020 American Physical Society. Received 7 July 2020; accepted 8 December 2020; published 21 December 2020. We are grateful to Steve Kivelson for a stimulating and insightful discussion. We thank Jason Alicea, Chenhao Jin, Patrick Lee, Stevan Nadj-Perge, Gil Refael, Alex Thomson, and Sagar Vijay for helpful conversations. We thank Yang Zhang, Noah Yuan, and especially Tongtong Liu for collaboration on related works, and Kin Fai Mak, Jie Shan, and Feng Wang for valuable discussions on experiments. It is our pleasure to thank the organizers of the KITP conference “Topological Quantum Matter: From Fantasy to Reality,” where this work was initiated. K.S. is supported by the Walter Burke Institute for Theoretical Physics at Caltech. L.F. is supported by the DOE Office of Basic Energy Sciences under Award No. DE-SC0018945, and in part by a Simons Investigator award from the Simons Foundation.
Group:Walter Burke Institute for Theoretical Physics
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Walter Burke Institute for Theoretical Physics, CaltechUNSPECIFIED
Department of Energy (DOE)DE-SC0018945
Simons FoundationUNSPECIFIED
Issue or Number:23
Record Number:CaltechAUTHORS:20200519-070724182
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103293
Deposited By: Tony Diaz
Deposited On:19 May 2020 17:02
Last Modified:16 Nov 2021 18:20

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