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When mobile impurities are introduced and coupled to a Fermi gas, new quasiparticles known as Fermi polarons are formed. There are two interesting, yet drastically different regimes of the Fermi polaron problem: (I) the attractive polaron branch, which connects to pairing phenomena spanning the crossover from BCS superfluidity to the Bose-Einstein condensation of molecules; and (II) the repulsive branch, which underlies the physics responsible for Stoner’s itinerant ferromagnetism. Here, we study Fermi polarons in two dimensional systems where many questions and debates regarding their nature persist. The model system we investigate is a doped MoSe2 monolayer. Remarkably, not only the energy splitting but also the quantum dynamics of attractive polarons agree with the predictions of polaron theory well. As the doping density increases, the quantum dephasing of the attractive polarons remains constant, indicative of stable quasiparticles, while the repulsive polaron dephasing rate increases nearly quadratically, as a consequence of the interplay between the electron Fermi seas in two valleys. The dynamics of Fermi polarons are of critical importance for understanding the pairing and magnetic instabilities that lead to the formation of rich quan- tum phases found in a wide range of physical systems including nuclei, cold atomic gases, and solids.

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• Creative Commons BY Attribution 4.0 International
  

Keyword: Fermi polarons, MoSe2 monolayer, quantum dynamics

Date published: 2023-03-02

Publisher: American Physical Society (APS)

Journal:

• Physical Review X (ISSN: 21603308) vol. 13 issue. 1 011029

Funding:

• U.S. Department of Energy
• Basic Energy Sciences DE-SC0019398
• National Science Foundation DMR-1808042
• National Science Foundation NNCI-2025227
• National Science Foundation DMR-1747426
• Materials Research Science and Engineering Center, Harvard University DMR-1720595
• Welch Foundation F-1662
• Australian Research Council DP210101652
• Centre of Excellence in Future Low-Energy Electronics Technologies, Australian Research Council CE170100039
• Army Research Office W911NF-17-1-0312
• Japan Society for the Promotion of Science 19H05790
• Japan Society for the Promotion of Science 21H05233
• National Science Foundation DMR-2122078
• Japan Society for the Promotion of Science 20H00354

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1103/physrevx.13.011029

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Updated at: 2025-02-23 22:47:02 +0900

Published on MDR: 2025-02-23 22:47:02 +0900