Observation and quantification of the pseudogap in unitary Fermi gases

• 成果类型: Article
• 署名作者: Li, Xi; Wang, Shuai; Luo, Xiang; Zhou, Yu-Yang; Xie, Ke; Shen, Hong-Chi; Nie, Yu-Zhao; Chen, Qijin; Hu, Hui; Chen, Yu-Ao; Yao, Xing-Can; Pan, Jian-Wei
• 署名单位: Chinese Academy of Sciences; University of Science & Technology of China, CAS; Chinese Academy of Sciences; University of Science & Technology of China, CAS; Chinese Academy of Sciences; University of Science & Technology of China, CAS; Chinese Academy of Sciences; University of Science & Technology of China, CAS; Hefei National Laboratory; Swinburne University of Technology
• 刊物名称: Nature
• ISSN/ISSBN: 0028-5517
• DOI: 10.1038/s41586-023-06964-y
• 发表日期: 2024-02-08
• 关键词: hubbard-model; normal-state; t-c; temperature; superconductivity; crossover; condensation; TRANSITION; BEHAVIOR; gap

摘要

The microscopic origin of high-temperature superconductivity in cuprates remains unknown. It is widely believed that substantial progress could be achieved by better understanding of the pseudogap phase, a normal non-superconducting state of cuprates1,2. In particular, a central issue is whether the pseudogap could originate from strong pairing fluctuations3. Unitary Fermi gases4,5, in which the pseudogap-if it exists-necessarily arises from many-body pairing, offer ideal quantum simulators to address this question. Here we report the observation of a pair-fluctuation-driven pseudogap in homogeneous unitary Fermi gases of lithium-6 atoms, by precisely measuring the fermion spectral function through momentum-resolved microwave spectroscopy and without spurious effects from final-state interactions. The temperature dependence of the pairing gap, inverse pair lifetime and single-particle scattering rate are quantitatively determined by analysing the spectra. We find a large pseudogap above the superfluid transition temperature. The inverse pair lifetime exhibits a thermally activated exponential behaviour, uncovering the microscopic virtual pair breaking and recombination mechanism. The obtained large, temperature-independent single-particle scattering rate is comparable with that set by the Planckian limit6. Our findings quantitatively characterize the pseudogap in strongly interacting Fermi gases and they lend support for the role of preformed pairing as a precursor to superfluidity. This study describes experiments with ultracold lithium Fermi gases in which many-body pairing leads to the emergence of a pseudogap, and it confirms theoretical predictions relevant to cuprate superconductivity.