Flawed but colorful diamonds are among the most sensitive detectors of magnetic fields known today, allowing physicists to explore the minuscule magnetic fields in metals, exotic materials and even human tissue.
“The new probe may shed light on high-temperature superconductors and help theoreticians crack this open question,” said coauthor Ron Folman of Ben-Gurion University of the Negev, who is currently a Miller Visiting Professor at UC Berkeley. “With the help of this new sensor, we may be able to take a step forward.”
Colorful diamonds, ranging from yellow and orange to purple, have been prized for millennia. Their color derives from flaws in the gem’s carbon structure: some of the carbon atoms have been replaced by an element, such as boron, that emits or absorbs a specific color of light.
Once scientists learned how to create synthetic diamonds, they found that they could selectively alter a diamond’s optical properties by injecting impurities. In this experiment, Budker, Folman and their colleagues bombarded a synthetic diamond with nitrogen atoms to knock out carbon atoms, leaving holes in some places and nitrogen atoms in others. They then heated the crystal to force the holes, called vacancies, to move around and pair with nitrogen atoms, resulting in diamonds with so-called nitrogen-vacancy centers. For the negatively charged centers, the amount of light they re-emit when excited with light becomes very sensitive to magnetic fields, allowing them to be used as sensors that are read out by laser spectroscopy.
Folman noted that color centers in diamonds have the unique property of exhibiting quantum behavior, whereas most other solids at room temperature do not.
“We hope to discover something new that cannot be seen with other technologies.”Ron Folman, Ben-Gurion University of the Negev in Israel.
“This is quite surprising, and is part of the reason that these new sensors have such a high potential,” Folman said.
Technology visionaries are thinking about using nitrogen-vacancy centers to probe for cracks in metals, such as bridge structures or jet engine blades, for homeland security applications, as sensitive rotation sensors, and perhaps even as building blocks for quantum computers.
Budker, who works on sensitive magnetic field detectors, and Folman, who builds ‘atom chips’ to probe and manipulate atoms, focused in this work on using these magnetometers to study new materials.
“These diamond sensors combine high sensitivity with the potential for high spatial resolution, and since they operate at higher temperatures than their competitors – superconducting quantum interference device, or SQUID, magnetometers – they turn out to be good for studying high temperature superconductors,” Budker said. “Although several techniques already exist for magnetic probing of superconducting materials, there is a need for new methods which will offer better performance.”
The team used their diamond sensor to measure properties of a thin layer of yttrium barium copper oxide (YBCO), one of the two most popular types of high-temperatures superconductor. The Ben-Gurion group integrated the diamond sensor with the superconductor on one chip and used it to detect the transition from normal conductivity to superconductivity, when the material expels all magnetic fields. The sensor also detected tiny magnetic vortices, which appear and disappear as the material becomes superconducting and may be a key to understanding how these materials become superconducting at high temperatures.
“Now that we have proved it is possible to probe high-temperatures superconductors, we plan to build more sensitive and higher-resolution sensors on a chip to study the structure of an individual magnetic vortex,” Folman said. “We hope to discover something new that cannot be seen with other technologies.”
Researchers, including Budker and Folman, are attempting to solve other mysteries through magnetic sensing. For example, they are investigating networks of nerve cells by detecting the magnetic field each nerve cell pulse emits. In another project, they aim at detecting strange never-before-observed entities called axions through their effect on magnetic sensors.
This story is reprinted from material from UC Berkeley, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.