Speaker:   

Bijuan Chen

Affiliation:   

Harvard University

Title: 

Quantum Imaging of the Local Diamagnetism and Stress in the High-Tc Superconductor La₃Ni₂O₇₋δ Under High Pressure

Date/Time:     

Thursday – April 17, 2025

11:00 AM

Zoom link

https://argonne.zoomgov.com/j/1618906752?pwd=M0ajZ7Gfr8crA0MfQNLbByiOvjP5GE.1

Abstract:

High-pressure research has been crucial in discovering novel superconductors and elucidating the mechanisms behind high-Tc phenomena. The recent observation of superconductivity in La₃Ni₂O₇₋δ—with an onset near 80 K at pressures above 14 GPa, exceeding the boiling point of liquid nitrogen—has sparked significant interest in the superconducting phases of Ruddlesden-Popper nickelates. Yet, the intrinsic nature of superconductivity in these materials remains ambiguous due to sample inhomogeneity, a limited superconducting volume, and sensitivity to local stress variations.

In this talk, I will present our research employing quantum imaging to investigate the local superconducting state and stress environment in La₃Ni₂O₇₋δ. By embedding nitrogen-vacancy (NV) centers directly into a diamond anvil, we integrate high-resolution optical microscopy for mapping local magnetic fields and stress with simultaneous in-situ transport measurements. This innovative approach overcomes the averaging limitations of conventional high-pressure magnetometry, delivering submicron-scale resolution without extensive background corrections. Our results reveal a strong spatial correlation between the onset of diamagnetism and uniaxial stress, while regions experiencing significant shear stresses show a pronounced suppression of superconductivity. These observations enable us to construct a comprehensive stress–shear–temperature phase diagram and, together with energy dispersive X-ray spectroscopy, demonstrate that superconductivity is confined to regions with the precise La₃Ni₂O₇₋δ stoichiometry. Ultimately, our work offers critical insights into the fundamental nature of superconductivity in this material, paving the way for a deeper understanding of the interplay between structure, stress, and superconductivity. Our work marks a substantial step forward in high-pressure physics, demonstrating the transformative potential of quantum imaging techniques for local-scale investigations of emergent quantum phenomena.

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