Norman Yao has designed a highly sensitive and accurate probe for assessing the performance of new materials under pressure and strain. His NV-DAC system integrates quantum spin defects directly into diamond anvil cells and enables the measurement of material properties under pressure with sub-micron spatial resolution at a wide range of temperatures.
Norman Yao received his A.B. and Ph.D. from Harvard University. He joined the faculty of the Department of Physics as an Assistant Professor in 2016, after completing postdoctoral research at UC Berkeley as a Miller Fellow. His laboratory employs a variety of theoretical, numerical and experimental tools to investigate problems at the interface between atomic, molecular and optical physics, condensed matter, and quantum information science.
Area of Research
The NV-DAC: A Quantum Sensor at High Pressures
Characterizing the behavior of matter under pressure and strain is essential for the development of next generation technologies, ranging from solar cells to auxetic and “smart” materials. The workhorse of such studies is the diamond anvil cell (DAC), which has had a transformative impact on materials science, chemistry, physics, and engineering by providing a tabletop apparatus capable of reaching megabar pressures. However, due to the enormous stress gradients generated, it is challenging to position a sensor near the sample in order to measure local material properties. This prevents access to essential pieces of information from within the sample chamber: for example, does material failure and fracture nucleate from a specific point? Are there inhomogeneities in the viscous and elastic properties of a sample? As a Bakar Fellow, Norman Yao will develop the NV-DAC system, which is capable of measuring material properties under pressure with sub-micron spatial resolution and at temperatures ranging from 4K to room temperature.
Squeezing a material between a pair of diamonds in the sample chamber of a diamond anvil cell (DAC) generates crushing pressures that can alter the material’s structure and create valuable new properties for a wide range of advanced technologies. DACs are also used to replicate conditions in the earth’s mantle to provide better understanding of seismic activity. But extracting critical information from within a DAC’s sample chamber demands sensors that can withstand pressures millions of times greater than what we experience on our planet’s surface.
In recent years scientists have turned a natural atomic flaw that exists in all diamonds into a versatile sensor technology. The flaw – called a “nitrogen-vacancy” or NV center – is created when two adjacent carbon atoms in the diamond crystal are replaced by a nitrogen atom and a vacant lattice site. The NV center can be utilized as a sensor because its energy levels and associated spectra are sensitive to strain, electric and magnetic fields. One of the critical advantages an NV center provides as a quantum sensor is its ability to measure fields at nanometer length scales. This is in stark contrast with conventional DAC technologies, which are limited to measuring bulk properties averaged over the entire DAC geometry.
Bakar Fellow Norman Yao, Assistant Professor of Physics, has overcome these conventional limitations with the invention of the NV-DAC, which directly integrates a thin layer of NV center sensors into a diamond anvil tip. With this invention, Yao and his group have been able to obtain highly sensitive and localized DAC measurements of a sample material’s properties under enormous pressure over a wide range of temperatures.
Q: What is unique about your use of NV centers in DACs?
A: Previously, DACs have been used to explore the effect of high pressures on the behavior of NV centers. In those studies, the main goal was to understand how the spectra of NV centers became modified at high strains. In our work, we use NV centers as a sensor to study the behavior of other materials as they undergo pressure-driven changes.
Q: What types of studies are made possible by the NV-DAC sensor?
A: One of the most promising directions for our NV-DAC sensor is to image magnetic fields emanating from materials within the high-pressure chamber. In order to do this, we have to carefully disentangle two effects: changes to the NV center as a result of being subjected to the high-pressure environment within the DAC; and the magnetic field signal coming from the sample of interest. Our ability to carefully account for the first effect precisely owes to previous measurements on NV center behavior as a function of pressure.
Q: Briefly, how does one make a DAC-NV sensor?
A: We start with a diamond anvil tip that has an intrinsically high density of nitrogen impurities within its crystal lattice. Then we bombard the diamond anvil using ion implantation of carbon atoms. We tune the energy of the carbon atoms so that they only penetrate a very short distance into the diamond lattice. This creates a high density of vacancies near the diamond’s tip to go along with the high density of nitrogen impurities. The final step is to get the nitrogen atoms and the vacancies adjacent to one another so that they form NV centers. This we do via an annealing recipe at temperatures up to 1,200 degrees Celsius.
Q: You’ve already used your DAC-NV sensor to study magnetic phases in iron and gadolinium, and to image stresses with a DAC’s sample chamber. These successes point to a wide range of possibilities for your NV-DAC sensor. What do you see as the most immediate applications?
A: On the magnetometry side of things, it would be exciting to use NV-DAC sensors to study the recently discovered room temperature superconductors, which are stabilized by extremely high pressures. Studying the phases of magnetic matter under such high pressures can, for instance, reveal new pathways to smaller, faster, and cheaper ways of storing and processing data. On the stress/strain imaging front, I would be thrilled to explore questions about how materials behave in extreme conditions. For example, how and why does fracturing occur? What is the microscopic nature of the glass transition?
Q: How will you use your Bakar Fellowship to advance the development of NV-DAC sensor technology?
A: The Bakar Fellowship will enable us to further develop key technical capabilities, such as demonstrating NV-DAC operation at pressures greater than 100 gigapascals, which is the pressure under which materials deep below Earth’s surface are formed. The Fellowship will also provide a tremendous opportunity to learn from a broad network of scientific, innovation and business development experts.