Recently, a research team lead by Xiaoxiang Xi at School of Physics, Nanjing University has made new progress in the study of the anomalous metallic state emerging from two-dimensional superconductors. By combining superconducting Higgs mode spectroscopy and low-temperature electrical transport techniques, the team detected experimental evidence of superconducting fluctuations in atomically thin NbSe₂, revealing the existence of localized electron pairing in the magnetic-field-induced anomalous metallic state. This work, titled “Unveiling Resilient Superconducting Fluctuations in Atomically Thin NbSe₂ through Higgs Mode Spectroscopy” was published in Physical Review Letters. The paper was selected as an “Editors’ Suggestion” and featured in the American Physical Society's Physics Magazine.

Two-dimensional superconductors are susceptible to fluctuation effects, manifesting in certain systems as an anomalous metallic state characterized by a longitudinal resistance significantly lower than that of the normal state, which persists down to the zero-temperature limit. This phenomenon contradicts the prediction from the scaling theory of localization that no metallic ground state exists in two-dimensional systems, and its underlying mechanism has remained unresolved. Limited by the sample size of two-dimensional superconductors, existing experimental studies on the anomalous metallic state have primarily relied on electrical transport measurements. To address this issue, the team systematically investigated the layered superconductor NbSe₂ using a combination of longitudinal resistance, Hall resistance, and Raman spectroscopy. They discovered that the anomalous metallic state arises from the fragile two-dimensional superconductivity, with superconducting fluctuations exhibiting unexpected robustness under applied magnetic fields. This result provides an important experimental basis for understanding the mechanism of the anomalous metallic state. The Higgs mode micro-spectroscopy method established in this work is expected to be applicable for studying other two-dimensional superconducting systems coexisting with charge density waves.

For details of the findings, please refer to the original article, Physical Review Letters 134, 066002 (2025), https://doi.org/10.1103/PhysRevLett.134.066002.