Ultra-cool technique maps local superconductivity under pressure

Harvard researchers added nitrogen-vacancy quantum sensors to diamond anvil cells to map micron-scale superconducting regions in nickelate samples under high pressure, and they report that superconductivity can appear in localized pockets and be suppressed by shear stress.

A team of Harvard physicists has adapted diamond anvil cell experiments by adding nitrogen-vacancy quantum sensors and used the setup to study nickelate superconductors under high pressure. The work, reported in Nature, combines a century-old high-pressure device with modern quantum defects in diamond to read tiny magnetic signals associated with superconductivity. Measurements were made at cryogenic temperatures inside a cryostat and use changes in diamond fluorescence to detect local magnetic effects known as the Meissner effect. The approach lets researchers map behavior at micron length scales and correlate local signals with pressure and stress. Key findings: - Researchers implanted nitrogen-vacancy centers in diamond anvils to function as local magnetic sensors. - The setup detected superconducting signatures at micron scales earlier than conventional resistance-based methods. - Superconductivity in the studied nickelate samples appeared in localized regions that grew with applied pressure. - Shear stresses were observed to limit or suppress superconductivity in parts of a single sample. - The experiments were conducted at high pressures (above 100 gigapascals in earlier work by the group) and at cryogenic temperatures. Summary: The work provides a new window into why some nickelate samples showed uneven superconducting behavior by revealing micron-scale variability and the role of mechanical stresses. Researchers say the tools enable more detailed local studies of superconducting materials; subsequent research directions reported include using these local measurements across varied compounds, pressures, temperatures, and compositions, with broader implications for understanding and engineering superconducting behavior.