The exact reason behind high-temperature superconductivity in cuprates, which are a type of material, is still a mystery at the microscopic level. Many scientists think that understanding the pseudogap phase, which is a normal non-superconducting state in these materials, could lead to significant progress in this area. One key question is whether the pseudogap comes from strong pairing fluctuations.
Unitary Fermi gases, in which the pseudogap—if it exists—necessarily arises from many-body pairing, offer ideal quantum simulators to address this question.
An international team of scientists has made a breakthrough discovery that could shed light on the microscopic mystery behind high-temperature superconductivity. It could also address global energy challenges.
In a recent study, Associate Professor Hui Hu from Swinburne University of Technology collaborated with researchers at the University of Science and Technology of China (USTC). Together, they conducted experiments that revealed the presence of pseudogap pairing in a strongly interacting cloud of fermionic lithium atoms.
This discovery confirms that multiple particles are pairing up before reaching a critical temperature, leading to remarkable quantum superfluidity. This finding challenges the previous notion that only pairs of particles were involved in this process.
Swinburne University of Technology’s Associate Professor Hui Hu said, “Quantum superfluidity and superconductivity are the most intriguing phenomenon of quantum physics.”
“Despite enormous efforts over the last four decades, the origin of high-temperature superconductivity, particularly the appearance of an energy gap in the normal state before superconducting, remains elusive.”
“The central aim of our work was to emulate a simple text-book model to examine one of the two main interpretations of pseudogap – the energy gap without superconducting – using a system of ultracold atoms.”
In 2010, scientists attempted to investigate pseudogap pairing with ultracold atoms. However, their experiment was unsuccessful. In this new experiment, researchers used advanced methods to prepare homogeneous Fermi clouds and eliminate unwanted interatomic collisions, along with precise control over magnetic fields.
These advancements enabled the observation of a pseudogap without relying on specific microscopic theories to interpret the data. The researchers found a reduction in spectral weight near the Fermi surface in the normal state.
According to researchers, “This discovery will undoubtedly have far-reaching implications for the future study of strongly interacting Fermi systems and could lead to potential applications in future quantum technologies.”
Journal Reference:
- Li, X., Wang, S., Luo, X. et al. Observation and quantification of the pseudogap in unitary Fermi gases. Nature 626, 288–293 (2024). DOI: 10.1038/s41586-023-06964-y