Nikola Maksimovic: Pushing the Boundaries of Quantum Materials
Assistant Professor Nikola Maksimovic (Physics) is a new faculty member at the Photonics Center. We sat down with him to learn a little bit about his life, his research, and who he is.
By Jack Osmond
*This interview has been edited for clarity and concision.
Can you tell me a bit about your background?
I was born in Boulder, Colorado. My parents are Serbian immigrants. I did my undergrad at CU Boulder, did my PhD at Berkeley, and came to Harvard for a postdoc. I was looking for faculty jobs, and I got a few offers. BU gave a pretty competitive package, there’s some cool stuff going on here, and I really like the Boston area, so, here I am.
Can you tell me a little bit about your research?
We do experimental physics. It’s basically the physics of materials: electronic properties of materials, magnetic properties, things like that.
What we do in my group is we combine two very different techniques. One is growth of materials — actually making them. We’re talking stuff like inorganic semiconductors, intermetallics, and metal oxides.
The other [technique] is we make these very sensitive, high-resolution microscopes, based on what are called quantum sensors, to image the magnetic or electronic properties of the materials.
Quantum sensors are basically these single atom defects that are trapped in semiconductors that are very coherent. You can engineer them and you can do very, very high-precision measurements of magnetic fields, for example, using these sensors. So, we can turn them into microscopes and then use them to image different properties of the materials we make.
What are the applications of your research?
The study of materials is a very old field and it’s very advanced. For example, all of our society is built on the semiconductor and computer chips: the Internet, AI, electrical lighting, solar panels, etc.
So, we actually understand quite a bit about the way that all these atoms come together and give you such-and-such property. That’s what we call emergence.
A bunch of atoms in there, they do something, and at the end of the day, you get a semiconductor. That’s an emergent property of all those billions and billions of atoms.
And the goal of my research is to look at the fringe cases, the materials which maybe exhibit some emergent properties that aren’t necessarily in a physics textbook. We’re trying to sort of push the boundaries of knowledge.
You have to work pretty hard to look for that, because people have been doing this for 150 years. You might have to go to extreme conditions, very low temperatures, high electric or magnetic fields. Maybe you have to confine the material to a single atomic layer.
What would be an example of a fringe-case property?
One would be in the field of magnetism. Take a typical magnet: Every atom inside that magnet has a little electron that’s creating a little magnetic moment. [When] all of the magnetic moments align, the whole thing behaves like one big bar magnet.
Now, let’s say you kind of create a special type of crystal structure, like a triangular lattice. You could end up with a magnet that has these magnetic moments at each node of the triangle, but they don’t necessarily want to align with each other. This one wants to point up. This other one wants to point down. The third one doesn’t know what to do. We call these types of structures “frustrated” magnets.
There are all kinds of emergent properties that frustrated magnets might have: complex spin textures, strong coupling to light or electric fields, or potentially highly quantum entangled states. You can think about using these frustrated magnetic systems to store or transmit classical or quantum information.
What drew you to this field of physics?
The thing I like about materials physics – what we call condensed matter physics – is it’s a very interdisciplinary field.
You have to take techniques from material science or chemistry or engineering. You have to have a breadth of knowledge, and you have to collaborate with other people who have very different training from you.
How are the Photonics Center’s tools and facilities enabling your research?
A lot of [what we do] is in the construction of these microscopes that we make out of these semiconductor defects. The way that you measure [with it] is you send light in, it hits the defect, and the defect emits light back out at you. There’s a lot of photonics and optics tools that we use in order to get light in and out.
The facilities in Photonics are very extensive. Materials characterization is something that we’ll need to do as we’re growing materials in the MSE Core facilities, for example. [Using] the OPF, Opto-Electronics Processing Facilities, we need to pattern very specific metal designs in order to also be able to drive the spin state of these defects. It’s a lot of the fabrication materials characterization facilities that we’ll be using in the Photonic Center.
Conceptually, understanding the way you relate that light to some other physical property that you’re trying to actually measure uses a lot of the theory from photonics.
What do you find to be unique about the Photonics Center?
The main thing that’s different [from other institutions] is that they put the user first. They don’t say, “how much money can we squeeze out of the people that are using this facility?” The user facilities are free. I think it’s far more open than any other places where I’ve done research.
It’s not only the facilities: it’s easy for me to go talk to people in the Photonic Center. It’s easy to talk to the students and faculty there. It’s easy for them to reach out to me and potentially work with me. That’s not true of every university. A lot of times there’s big barriers.
How is it going, forming your lab group? Are you still looking for students?
At the moment, I’m full on graduate students. I am interested in taking on undergrads and masters students. I think that next year I could take on another graduate student.
What qualities or areas of interest are you looking for in undergrad students?
It’s very hands-on research, so, if you want to work in the lab you have to be excited to work with hardware. You’re constantly designing or troubleshooting something in the lab. There’s not a whole lot of sitting behind your desk and writing code that does X, Y, or Z. Materials growth is very hands-on. Building these quantum sensor microscopes is very hands-on.
You have to be resilient to the problems that arise in the real world. Experiments are hard. So, you have to be comfortable with constantly failing. It’s failure 90% of the time, and then slow, incremental progress.
As far as research interests, we’re looking for new fundamental phenomena in materials. It’s more about the pursuit of knowledge. [We’re doing] basic science.
Is that your favorite part of the research, uncovering this more fundamental knowledge?
The semiconductor came from fundamental research in the 20s, for which it wasn’t clear there was any point in doing. They were just trying to understand how electronic band structures arise from quantum mechanics. And then 30 years later, you get the computer! And 50 years later, you’ve got the internet.
You know deep down, based on history, that if you do very fundamental work in materials, 20 years down the line, it is going to get picked up and have a big impact.
Now a bit about you. When you’re not in the lab or in the classroom, what do you like to do?
I’m a stereotypical physicist: I like rock climbing, backpacking, skiing, anything outdoors in the mountains. I grew up in Colorado. So, that’s what I grew up doing.
[My favorite place to backpack is] the White Mountains, Franconia Ridge. I go up there a few times a year. It’s surprisingly brutal, actually. I find it more strenuous in a lot of ways than walking up taller stuff in the West. I don’t know what it is. I think it’s that the weather’s kind of crazy here.