The Inside Scoop on the World’s First Room Temperature Superconductor
In this exclusive interview we explore the discovery of the world’s first room-temperature superconductor with Dr. Ranga Dias, Assistant Professor of Mechanical Engineering and Physics & Astronomy at the University of Rochester. He joins us to describe his team’s historic achievement of room temperature superconductivity in an organically-derived carbonaceous sulfur hydride at a remarkable 58 degrees Fahrenheit and a crushing pressure of 39 million psi.
Ranga, welcome! Let me begin by asking a bit about your background, and what inspired you along the career path that led to your research in room-temperature superconductivity?
Thank you, Tim. It’s a pleasure to talk with you about our recent discovery. I’m originally from Sri Lanka, and even back in middle school I was fascinated with science, and I was a member of the Astronomy and Space Study Center, bringing together different age groups of students to learn about science.
I joined that club when I was 12 years old, and my curiosity only grew from there. I’d always been fascinated by science and chemistry, and over time that interest grew to encompass physics. I had no idea at the time where that would take me, but it put me on a path to a career in science, and it’s the inspiration that eventually led to my role at here at the University.
I did my undergraduate work at the University of Colombo in Sri Lanka and later completed my PhD in physics at Washington State University. After that, I did postdoctoral studies at Harvard University with Professor Isaac Silvera and then become a professor here at the University of Rochester.
You’ve succeeded in creating room temperature superconductivity in carbonaceous sulfur hydride at a temperature of 58° Fahrenheit (14° C). Before this experiment, I’ve read that the highest temperature achieved was 203 kelvin (-70° C) in hydrogen sulfide (H₂S). Would it be accurate to call this a historic first for science, and how much time and research has it taken for you to reach this milestone?
You can definitely say this is a landmark achievement, we’ve been waiting for this day for over a century since superconductivity was first discovered in 1911. Before our discovery, the previous records were recently set in 2015 by Mikhail Eremets at the Planck Institute at a temperature of 203 kelvin (-70 °C), and again in 2019 at 250 kelvin (-23 °C) using lanthanum hydride.
These recent achievements gave us new data to work with, and I wanted to apply that to a carbon-sulfur material, which has always fascinated me because of the multivalent nature of carbon. I’d found superconductivity in carbon disulfide, and had the idea that carbon and sulfur might hold the key to unlocking the secret of room temperature superconductivity.
In addition to carbon and sulfur, hydrogen is also an important element, because metallic hydrogen was theorized to be a room-temperature superconductor, but only under enormous amounts of pressure. We started thinking about how to reduce the required pressure down to something that is experimentally accessible while retaining the metallic hydrogen properties. Instead of mechanically compressing the hydrogen to enormous pressures, we decided to attempt chemically compressing it instead.
You can visualize the difference between mechanical and chemical compression by imagining yourself inside sitting an empty room with 4 walls. If you move the walls closer together, eventually you’ll get squeezed, and this is what you might think of as mechanical compression. However, another way to create pressure is by filling up the room with other people without changing the size of the room itself. That’s chemical compression, and it’s more experimentally attainable than mechanical compression.
Carbon and sulfur are perfect candidates to chemically compress hydrogen because they allow us to make a covalent metal and carbon also allows you to make multiple bonds and has a high coordination number to help create a superconducting state.
I’ve been interested in carbon and sulfur for over a decade, and I gained experience working with pure hydrogen at Harvard. Those were the theoretical starting points for this experiment, combined with the extensive research we’ve undertaken at the University of Rochester.
For the layperson who may not be familiar with the applications of superconductivity, at the very least this could offer an improvement to the electrical grid by eliminating conductive resistance. What are some of the other uses for superconductivity that have helped inspire your work?
Superconductors have no electrical resistance, but another interesting property they have is the Meissner Effect, or what’s called “perfect diamagnetism”. This is the superconductor’s ability to completely expel an externally applied magnetic field, and that’s what lets you levitate a superconductor in a magnetic field. This is the principle behind Maglev trains that floats above the tracks and achieve speeds of nearly 300 miles per hour.
Maglev technology already exists but requires cryogenic systems to cool the superconductors, and the costs to operate it are very expensive. Imagine the applications that become possible if we could build maglev devices that operate at room temperature. I would say that transportation will be dramatically changed.
Medical imaging is another big area where superconductors are used for tools such as MRI machines, but just like maglev there’s a lot of costs that go into cryogenics, and the liquid helium used for cooling is non-renewable. So, using room-temperature superconductors will let us improve medical imaging systems by eliminating the cryogenics
Another application I can think of is in consumer electronic devices. Imagine building superconducting circuits without any power loss or heat dissipation. This would let these components run faster and could transform devices like computers and smartphones. Even in quantum computing, there are indications that we can use superconducting cubits at room temperature. This technology could transform electronics, and we could go from what you might call a semiconducting age to the superconducting age.
I’d like to ask a bit about the team that you worked with on this. So, you’re with the University of Rochester and you work in both the Mechanical Engineering and Physics & Astronomy departments. Who were some of the notable colleagues who helped you with this experiment, and what kind of background specializations did they come from?
My team is composed of graduate students from a variety of backgrounds in engineering and physics. They’re all trained to do high-pressure experiments and have worked hard to set up our laboratory and develop our experimental techniques. My students have invested a lot of effort in getting our program to where it is today, and they’re deeply involved in the research.
I’m also grateful for the assistance and mentorship of Professor Rip Collins, a senior faculty member at the university who helped guide me through the process of building a research area. When you’re just getting started, it helps to have guidance, and he truly helped me get things rolling.
I’ve also enlisted the help of a colleague I worked with back at Harvard who is an expert in X-ray crystallography. The light elements we’re working with make it difficult to understand the crystal structure of our superconducting material using traditional X-ray diffraction methods, so he’s developing new techniques to help us do precise structural studies.
Let’s talk about the sample: Phys.org described this as an “organically-derived carbonaceous sulfur hydride” that you created by combining hydrogen with carbon and sulfur. What led you to this particular chemical compound, and what makes it suitable as a room-temperature superconductor?
That’s a great question. Back in 2002, superconductivity was discovered at 39 kelvin (-243 °C) in magnesium diboride (MgB₂). It is a pure, covalent-type metallic-state material, and shows us two things that can be very favorable for superconductivity — lighter elements and strong bonds. Hydrogen, of course, is the lightest element and makes strong hydrogen bonds, and carbon and sulfur are the best candidates to create a covalent metal.
Now, covalent metals are rare at ambient pressures, but they can be made with pressure because of the properties of carbon and sulfur, along with hydrogen. So, we experimentally created a pressure of 400 gigapascals and then initiated photochemical synthesis with a green laser to produce a beautiful, transparent crystal composed of carbon, sulfur, and hydrogen, which was the material for our room-temperature superconductor.
Now when most people think of superconductors, YBCO materials come to mind that are created by a sintering process in an electric kiln. The carbonaceous sulfur hydride you describe required pressure to make, however — over 39 million pounds per square inch. Is the chemistry of this superconductor similar to others in any way, and why was such enormous pressure required to make it?
The mechanism behind these two types of superconductors is very different. YBCO is a cuprate superconductor, but carbonaceous sulfur hydride is more like a conventional superconductor, which follows the BCS model. These are two completely different paths to the goal of superconductivity.
Again, in our material, we need to make a covalent metal before it becomes superconducting, and we can’t create this at ambient pressure. However, if you take an insulator and increase the pressure, the valence band and conduction bands get broader and broader, and at some point, they’ll cross.
When the valence bands cross and overlap, you’ll get an insulator to metal transition. We use pressure to generate metals, which creates enough electron density for this high level of conductivity, and also the appropriate structure to have this high electron form of coupling to be a superconductor.
Using pressure lets us tweak the molecular structure of our material in a variety of ways. You know, there are some bonds or structures that may not be even possible to think of at ambient pressure, but with increasing pressure, you, you may be able to easily create things that you never thought possible. To get optimal conditions, which gives you the optimal structure, you need pressure, which is why we use it.
You used something called a diamond anvil cell to generate the pressure required for this experiment. Can you describe how this device generates such tremendous pressure and did the superconductive effect in your sample persist after the pressure was removed?
The diamond anvil cell is very simple device. As the name implies, it uses two anvil-shaped diamonds with very small tips that face each other and have our superconducting sample placed between them. We use diamond because it’s the strongest material we know of and it’s transparent, so we can see through it and study what’s happening in realtime when we apply pressure.
In simple terms, pressure is force divided by area, so the smaller an area you have at the diamond’s tip, the higher the pressure you can generate. In our case, the area at the tip is only 100 microns in size, which means that applying only a small force to the diamond’s base lets us generate enormous pressure.
In our experiment, we placed a small sample chamber surrounded by a gasket in between the two diamond anvils, and then we mechanically pressed them together by gradually tightening 4 screws on the press using an Allen key. People sometimes think it takes an enormous device to generate all this pressure, but you can actually hold the diamond anvil press in your hand and still achieve the same pressure found at the center of the earth.
Now in terms of releasing the pressure, we did not test whether the superconductive effect persisted when we released the pressure because we were trying to push the experiment as high as mechanically possible. We did this carefully because at those pressures even diamonds will sometimes break. Unfortunately, this means that don’t know whether our sample would revert back to the original material or if it would remain superconductive.
Now I understand that the test sample was measured in picoliters, which made it about the size of an inkjet particle. How do you measure the electrical resistance and superconducting properties of something so small, and what kind of margin for error is there in those measurements?
Our sample size was very small, around 30 microns in area and only a few microns thick. To perform electrical measurements we used tiny electrodes with a tip size of about 2 microns. They’re so small that we had to use a high-zoom microscope just to get them placed on the sample. Once they were placed, we pressurized the experiment which made contact with the sample.
After we had our electrodes in contact with the sample, we were able to easily measure voltage and current using an oscilloscope, which let us calculate the resistance. We also ran tests on the sample with a few other techniques using more modern technology using methods we developed to work with the tiny electrodes and sample size in our experiment.
Have you considered other methods for producing the superconductor that may not require as much pressure, or might allow a larger sample yield? Is there a possibility that some kind of chemical vapor deposition or sputtering-deposition process like the type used to grow diamonds on various substrates?
Yes, you’re spot on with that. Let me give you an example based on the diamond I mentioned earlier. Diamond is a high-pressure form of carbon, but it’s metastable, which means that when you release the pressure that’s required to make it, it doesn’t simply revert back to its original carbon form, instead it remains a diamond.
Pressure used to be required to make diamond, but eventually people found a way to grow diamonds in the laboratory. Just like you mentioned using chemical vapor deposition, you can grow a diamond atom by atom in the lab.
Once we better understand the structure and chemistry of our material, it’s likely that techniques such as chemical vapor deposition (CVD) and molecular-beam epitaxy (MBE) will allow us to grow large quantities of our room temperature superconductor for real-world applications.
For real-world applications, making superconductive wire comes to mind, but since you mentioned moving from a semiconductor world to a superconductor world, do you think it’s possible to have superconductors printed as part of the chip fabrication process?
Yes, I definitely think it’s possible. The big question is how we can make superconductive wire from carbon and sulfur materials. Do we need a more ductile material in order to make a wire? Will the same chemistry work, or do we need other elements?
There are lots of questions we need to answer, but keep in mind that what we currently have is a high-pressure form of this material. Will it still perform at normal pressures? Before we can answer questions about wire, we need to determine how to make this material superconductive at ambient pressure.
In order to achieve this, we may have to substitute other materials using a process we call chemical tuning. Maybe selenium will do the job instead of sulfur, or perhaps something completely different such as lanthanum, yttrium, or scandium. We’ll begin using our current sample and tweak the composition to create a material that can be used for real-world applications, so our final product may have a very different composition.
I also wanted to ask about the upper-field limit and critical current density: if I understand it correctly, these are the limits to the maximum magnetic field strength and current density that a superconductor can handle before it breaks down. Did you measure these, and were they similar to a conventional sintered superconductor?
Yes. We don’t have a magnetic field that goes high enough to measure the upper-field limit, but we did test the sample with a magnet that goes up to nine tesla. Then we applied the standard superconducting model in the Ginzburg–Landau theory and extrapolated that the high critical field would be at 62 tesla, which is a very high value.
We also haven’t directly measured the critical current density yet, which we plan to do in future experiments. However, based on my rough calculations, our sample should perform like a conventional MGB₂ superconductor with both a high critical current density and a high critical magnetic field limit.
Based on what we know so far, our superconductor should work very much like MGB₂ or even Niobium, which will make them useful for practical applications requiring a high current density and high magnetic field limits. So, even if this particular room temperature superconductor doesn’t end up being useful for commercial applications, our early calculations and studies tell us that we’re going in the right direction.
Let me close by asking what comes next. You’ve got a lot of new data for computer modeling and you’ve mentioned pursuing commercially viable ductile wire at ambient pressure & temperatures. Is that next in the quest for room temperature superconductivity?
Computer modeling helps us do some of the material research and theoretical predictions, which definitely helps our research. Another very important breakthrough was the realization that hydrogen plays a large role in superconductivity, which was overlooked for the last couple of decades.
The renewed focus on hydrogen was inspired by Eremets’ 2015 paper, which initiated a paradigm shift that’s inspiring a lot of change. It’s taken us in a totally different direction with many promising results. So computational power plays a role, but a deeper understanding of the mechanisms in superconductivity is definitely helping us to achieve success more rapidly.
I think we have a very good chance of producing a room-temperature superconductor for commercial applications. You know, superconductors have been around for more than a century, and for most of that time, research has progressed very slowly. However, this changed in 2015, and discoveries are happening rapidly now. There’s a lot of excitement in superconductivity research right now, and I think we’ll see a commercial room-temperature superconductor before too long.
About Our Guest
Professor Ranga Dias received his B.S. from the University of Colombo, Sri Lanka in 2006 and his Ph.D. in physics from Washington State University in 2013. He joins the University of Rochester after a postdoctoral fellowship in the Department of Physics at Harvard University, where he investigated the quantum phenomena in hydrogens at extreme conditions.
Dr. Dias is an internationally recognized scientist in the field of high pressure physics, and his work has also been reported in popular press, e.g. New York Times, BBC, NBC, NPR, Physics Today, New Scientist, Chemistry World, Science News, and Nature News and Views. Learn more about him at his University of Rochester faculty page.
