Teams of Professor Nie Jiacai and Professor Liu Haiwen from the School of Physics and Astronomy, Beijing Normal University, have published a paper titled "Anisotropic Upper Critical Field beyond the Pauli Limit in a Nickelate Superconductor: Evidence for a Quantum Fluctuation-Driven State" in the international journal Physical Review Letters, which was selected as an Editors' Suggestion.

The research established a microscopic mechanism where heavy-fermion mass renormalization suppresses orbital pair breaking, enabling disorder-enhanced quantum fluctuations to preserve superconductivity far beyond the Pauli limit.

The abstract of this paper is as follows:

Superconductivity can be destroyed by a magnetic field with an upper bound known as the Pauli limit. Here, we report a large violation of the Pauli limit in both in-plane and perpendicular magnetic fields in La_0.8⁢Sr_0.2⁢NiO₂ infinite-layer superconducting thin films. The critical field H_c2 shows a clear anisotropic behavior and a pronounced upturn at ultralow temperatures, manifesting anisotropic superconductor-metal transition features. Scaling analysis near the T → 0 quantum critical point of this transition reveals a quantum Griffiths singularity arising from quenched disorder, hallmarked by a diverging dynamic critical exponent. These quantum Griffiths singularity induced quantum fluctuations provide the origin for the pronounced H_c2 upturn and represent a key intrinsic mechanism for the robust violation of the Pauli limit. Our findings establish a microscopic mechanism where heavy-fermion mass renormalization suppresses orbital pair breaking, enabling disorder-enhanced quantum fluctuations to preserve superconductivity far beyond the Pauli limit.

Reference: https://journals.aps.org/prl/abstract/10.1103/mmpn-gl8z