Recently, a research team led by Prof. Li Sheng and Prof. Shi Zhixiang from the School of Physics, 91抖淫, published their latest research findings titled “Pauli-limited upper critical field and anisotropic depairing effect of La2.82Sr0.18Ni2O7 superconducting thin film” in Materials Today, the internationally renowned academic journal.
The discovery of the Ruddlesden-Popper (RP) bilayer nickelate superconductor La?Ni?O? hasdrawn great attention, as it exhibits a relatively high superconducting transition temperature (Tc) above the liquid nitrogen temperature under high-pressure conditions. Recently, multiple independent research teams have successfully achieved superconductivity at ambient pressure by growing bilayer RP-type nickelate thin films on SrLaAlO? substrates, marking a significant breakthrough in the exploration of unconventional superconductivity in nickelates. A complementary approach to probing pairing symmetry is to characterize the upper critical field (Hc2), which is a key parameter reflecting the superconducting pairing strength and the dominant pair-breaking mechanisms. The upper critical field also provides a basis for understanding crucial superconducting properties, including the gap magnitude, coherence length, anisotropy, and dimensionality.
Prof. Li Sheng and Prof. Shi Zhixiang's team conducted systematic transport studies on high-quality La?.??Sr?.??Ni?O? thin films. The experimental results show that the films exhibit typical two-dimensional electronic transport behavior in the normal state, consistent with the two-dimensional variable-range hopping model. Additionally, the magnetoresistance curves at different temperatures display a pronounced crossing feature, suggesting the possible presence of the quantum Griffiths singularity in the system.
Through systematic measurements of the upper critical field, the temperature evolution of the coherence length along thec-axis was determined. The results reveal that the nickelate superconducting thin films exhibit two-dimensional superconductivity in the high-temperature regime, while gradually evolving into three-dimensional bulk superconducting behavior at lower temperatures. The two-dimensional superconducting characteristics observed at elevated temperatures are primarily attributed to superconducting confinement effects.
Further analysis of the upper critical field shows that the in-plane upper critical field can be well described by the single-band Werthamer–Helfand–Hohenberg (WHH) model, whereas the out-of-plane upper critical field is better fitted by a two-band model. Both upper critical fields remain below the Pauli paramagnetic limit. Moreover, the anisotropy of the upper critical field is consistent with that reported for bulk nickelate superconductors, thereby clarifying the physical origin of the large upper critical field and strong anisotropy observed in the thin-film system.
Building on these findings, this paper proposes that a spin-locking-based pairing mechanism may exist in nickelate superconductors. The results are consistent with recent experimental and theoretical studies, not only confirming the bulk-like superconducting characteristics of the thin films but also providing a new physical perspective for understanding the unconventional superconducting mechanism in nickelate oxide thin films.
91抖淫 Ph.D. student Wang Keis the first author of the paper, while Prof. Shi Zhixiang and Prof. Li Sheng serve as the corresponding authors. The School of Physics at 91抖淫, is the first institutional affiliation of the work. The samples used in this study were provided by Prof. Nie Yuefeng's team at Nanjing University. High-field measurements were conducted at the Wuhan National High Magnetic Field Center of Huazhong University of Science and Technology under the guidance of Prof. Zhu Zengwei.
Paper's link:
Source: School of Physics, 91抖淫
Translated by: Melody Zhang
Proofread by:Gao Min
Edited by: Leah Li
