New tool combines quantum sensors and pressure sensors to precisely detect superconductor properties

According to a paper published in the latest issue of Nature magazine, Harvard University in the United States has developed a basic tool for accurately measuring superconductors. They creatively integrated quantum sensors into standard pressure sensing equipment to directly read the electrical and magnetic properties of pressurized materials.

The repulsion of magnetic fields by high-pressure superconductors can be detected using nitrogen-vacancy centers in diamond anvil cells (Artistic image).
Image credit: Ella Malushenko/AAAS website

Hydrogen behaves strangely under pressure. Theory predicts that this normally gaseous element will become metallic or even superconductor under pressures of more than 1 million atmospheres. Scientists have long been eager to understand superconducting hydrogen-rich compounds (called hydrides) and eventually use them for practical purposes, including levitating trains and particle detectors. However, these materials are difficult to study with existing methods, and it is even more difficult to measure them accurately.

The new tool developed by the Harvard University team can not only measure the behavior of hydride superconductors under high pressure, but also image them.

The standard way to study hydrides at extreme pressures is to use a diamond anvil cell, which squeezes a small amount of material between two brilliant-cut diamond interfaces. To detect when a sample has been squeezed enough to superconduct, one typically looks for two signatures: a drop in electrical resistance to zero, and a repulsion of any nearby magnetic field (a.k.a. the Meiners effect).

To apply the necessary pressure, researchers must secure the sample with a gasket to distribute the squeeze evenly, then seal the sample in a chamber. But this makes it difficult to actually observe the dual signature of superconductivity.

To get around this problem, the researchers designed and tested a clever modification: They integrated a thin layer of sensors directly onto the surface of a diamond anvil cell. The sensors are made from naturally occurring defects in the diamond atomic lattice. They used these efficient quantum sensors, called nitrogen-vacancy centers, to image regions within the cavity as the sample was pressurized and entered a superconducting regime. To prove their concept, the researchers used cerium hydride, a material known to become a superconductor at pressures of about 1 million atmospheres.

The new tool will not only help scientists discover new superconducting hydrides, but also make it easier to study existing superconducting materials.

How severe is extreme pressure? On Titan, Saturn's sixth satellite, there is a natural gas lake, which is caused by the extreme pressure environment on Titan, which makes the air "deteriorate". In comparison, the pressure we are under in our work and life is nothing. When the pressure is extreme enough, as described in this article, hydrogen can also become metallic and even show superconductivity. This hydride superconductor is very attractive and may provide unlimited applications for humans in the future, but scientists must accurately understand its properties, which is the significance of quantum sensing measurement tools.