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; Jian-Wei Pan

doi:10.1038/s41586-023-06964-y

Observation and quantification of the pseudogap in unitary Fermi gases

Nature. 2024 Feb;626(7998):288-293. doi: 10.1038/s41586-023-06964-y. Epub 2024 Feb 7.

Authors

Xi Li^#^{1

2

3}, Shuai Wang^#^{1

2}, Xiang Luo^{1

2}, Yu-Yang Zhou^{1

2}, Ke Xie^{1

2}, Hong-Chi Shen^{1

2}, Yu-Zhao Nie^{1

2}, Qijin Chen^{1

2

3}, Hui Hu^{1

4}, Yu-Ao Chen^{5

6

7}, Xing-Can Yao^{8

9

10}, Jian-Wei Pan^{11

12

13}

Affiliations

¹ Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China.
² Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China.
³ Hefei National Laboratory, University of Science and Technology of China, Hefei, China.
⁴ Centre for Quantum Technology Theory, Swinburne University of Technology, Melbourne, Victoria, Australia.
⁵ Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China. yuaochen@ustc.edu.cn.
⁶ Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China. yuaochen@ustc.edu.cn.
⁷ Hefei National Laboratory, University of Science and Technology of China, Hefei, China. yuaochen@ustc.edu.cn.
⁸ Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China. yaoxing@ustc.edu.cn.
⁹ Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China. yaoxing@ustc.edu.cn.
¹⁰ Hefei National Laboratory, University of Science and Technology of China, Hefei, China. yaoxing@ustc.edu.cn.
¹¹ Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei, China. pan@ustc.edu.cn.
¹² Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai, China. pan@ustc.edu.cn.
¹³ Hefei National Laboratory, University of Science and Technology of China, Hefei, China. pan@ustc.edu.cn.

^# Contributed equally.

PMID: 38326594
DOI: 10.1038/s41586-023-06964-y

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 cuprates^1,2. In particular, a central issue is whether the pseudogap could originate from strong pairing fluctuations³. Unitary Fermi gases^4,5, 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.