Quantum noise spectroscopy of superconducting dynamics in a cuprate thin film

Abstract

Characterizing the low-energy dynamics of quantum materials is crucial for understanding strongly correlated electronic states, yet remains experimentally challenging, particularly in two-dimensional systems. Here, we leverage nitrogen-vacancy (NV) centers in diamond as a non-invasive quantum sensor to study thin-film Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$ (BSCCO), revealing several distinct dynamical phenomena across the superconducting phase diagram. At zero magnetic field and low temperatures, NV depolarization ($T_1$) spectroscopy captures GHz-scale noise from nodal quasiparticle excitations, consistent with Bardeen--Cooper--Schrieffer (BCS) mean-field theory. Near the critical temperature $T_c\approx 90$ K, supercurrent-fluctuation-induced noise sharply reduces $T_1$. By analyzing the temperature scaling of $T_1$, we observe clear deviations from mean-field prediction, reflecting the importance of order parameter fluctuations and enabling the determination of critical exponents. Under a small magnetic field, a broad and asymmetric reduction of $T_1$ unveils a liquid-like phase of mobile vortices. NV decoherence ($T_2$) spectroscopy further probes MHz-scale noise and reveals complex vortex-solid fluctuations well below $T_c$. Our results establish quantum noise spectroscopy as a non-invasive probe of superconducting dynamics over frequency and length scales complementary to existing techniques.

arXiv comment[Version 3] manuscript revision with additional experiments. 10 pages, 4 figures in main; 6 pages, 2 figures in methods; 16 pages, 15 figures in supplementary information. [Version 2] revised with methods and supplementary information. 9 pages, 4 figures in main; 4 pages, 2 figures in methods; 7 pages, 5 figures in supplementary information. [Original Version] 9 pages, 4 figures in main text