International Team Measures Charge Carrier Interactions in Superconductors

A recent study conducted by an international research team at BESSY II has advanced the understanding of high-temperature superconductivity by measuring the energy of charge carrier pairs in undoped La2CuO4. The findings indicate that the interaction energies within the superconducting copper oxide layers are significantly lower than those in the insulating lanthanum oxide layers. This research, published on November 7, 2025, in the journal Nature Communications, could have implications for future studies on superconductors and other functional materials.

High-temperature superconductors have fascinated scientists for nearly four decades due to their ability to conduct electricity without resistance at temperatures above absolute zero, and occasionally at temperatures approaching room temperature. Despite their practical applications, the mechanisms underlying this phenomenon remain elusive. The established understanding highlights that specific interactions between charge carriers facilitate their movement through the crystal lattice under particular conditions.

Led by Professor Alexander Föhlisch, the research team embarked on an experiment to assess the interactions between charge carriers in the different oxide layers of La2CuO4. The samples, supplied by the University of Rome, consist of alternating copper oxide and lanthanum oxide layers. Doping this compound with foreign atoms can induce superconductivity at temperatures below 40 Kelvin, while the insulating lanthanum oxide layers do not contribute to this property.

In this study, the team focused on undoped La2CuO4 at room temperature. “We aimed to understand the strength of the interactions between charge carriers in the two oxide layers and how they differ,” noted Dr. Danilo Kühn, the study’s first author. The measurements utilized sophisticated time-of-flight spectrometers configured to detect electron pairs through Auger photoelectron coincidence spectroscopy. The team employed unique X-ray pulses, known as PPRE pulses, to strike the sample at intervals of several hundred nanoseconds, allowing for precise observation of rapid interaction processes.

The results indicated that the interaction energies were markedly lower in the copper oxide layer, a key component in high-temperature superconductivity, compared to the insulating lanthanum oxide layers. “These findings enhance our comprehension of the mechanisms involved in high-temperature superconductivity,” stated Professor Föhlisch. He further emphasized that this measurement technique could yield valuable insights into other functional materials as well.

This research not only sheds light on the complexities of superconductivity but also paves the way for future exploration of materials that could revolutionize technologies reliant on lossless electrical conduction. The implications of these findings could extend beyond superconductors, encouraging further investigation into the properties of various functional materials.

For more information, refer to the original study by Danilo Kühn et al., titled “Direct observation of the on-site oxygen 2p two-hole Coulomb energy in La2CuO4,” published in Nature Communications.