Unveiling resilient superconducting fluctuations in atomically thin NbSe${}_2$ through Higgs mode spectroscopy

Abstract

We report a combined electrical transport and optical study of the superconductivity in atomically thin NbSe${}_2$. When subjected to an out-of-plane magnetic field, an anomalous metallic state emerges, characterized by a finite longitudinal resistance and a vanishing Hall resistance, suggesting the presence of particle-hole symmetry. We establish a superconducting Higgs mode in atomically thin samples, which reveals enduring superconducting fluctuations that withstand unexpectedly high reduced magnetic fields. These findings provide evidence of robust locally paired electrons in the anomalous metallic state, affirming its bosonic nature.