Observation and quantification of the pseudogap in unitary Fermi gases

Xi Li, Shuai Wang, Xiang Luo, Yu-Yang Zhou, Ke Xie, Hong-Chi Shen, Yu-Zhao Nie, Qijin Chen, Hui Hu, Yu-Ao Chen (), Xing-Can Yao () and Jian-Wei Pan ()
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Xi Li: University of Science and Technology of China
Shuai Wang: University of Science and Technology of China
Xiang Luo: University of Science and Technology of China
Yu-Yang Zhou: University of Science and Technology of China
Ke Xie: University of Science and Technology of China
Hong-Chi Shen: University of Science and Technology of China
Yu-Zhao Nie: University of Science and Technology of China
Qijin Chen: University of Science and Technology of China
Hui Hu: University of Science and Technology of China
Yu-Ao Chen: University of Science and Technology of China
Xing-Can Yao: University of Science and Technology of China
Jian-Wei Pan: University of Science and Technology of China

Nature, 2024, vol. 626, issue 7998, 288-293

Abstract: Abstract 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.

Date: 2024
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DOI: 10.1038/s41586-023-06964-y

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