Rakheja revealing the secrets of new materials

When new materials are discovered, how do people figure out what they’re good for, and how to use them most effectively? CSL faculty member Shaloo Rakheja is pursuing a rich portfolio of efforts to model the physics and functionality of nanoscale devices that leverage new materials.

Rakheja, who joined the Department of Electrical and Computer Engineering and CSL as an assistant professor in Fall 2019, is the principal investigator of the projects “Toward

Energy-Efficient Heterogeneous Computing: Integrating Polymorphic Magnetic and CMOS Devices” (funded by the National Science Foundation in Fall 2019) and “Modeling and Simulation of Wide Bandgap Photoconductive Switches for RF Applications” (funded by the Department of Energy via the Lawrence Livermore National Lab). At the same time, she’s also serving as a co-PI on “Antiferromagnetic Magneto-electric Memory and Logic” (jointly funded by SRC and the National Science Foundation via the University of Nebraska–Lincoln).

“My research is mainly in dealing with new types of materials and what types of new functionality and physics we can get from these materials in order to create better products—better electronics which could have better energy efficiency or some higher form of functionality that is not currently available in the devices that we use,” said Rakheja, who is also affiliated with the Nick Holonyak Jr., Micro and Nanotechnology Lab.

While she admits that “you can spend your entire career looking at one material,” she is enthusiastically pursuing work on a diverse range of materials with very different potential applications.

In her project with Lawrence Livermore, she is examining wide-bandgap semiconductors, which are very unlike the semiconductors used in everyday electronic devices like laptops. Because of their wider bandgaps, they have the ability to withstand harsh, even extreme, environments, such as very high temperatures or electric field gradients. In Rakheja’s part of the project, she’s using a theoretical modeling framework to shed light on the non-equilibrium dynamics that occur in these semiconductors under such extreme input stimuli.

Eventually, her work will inform the use of these materials not just in extreme environments or high-power electronics, but also, because electron velocity in these materials is very high, in applications that require a very high frequency of operation. Ultimately, her work should enable creation of devices that can operate much faster than the devices of today.

In her project with Nebraska, Rakheja is again looking at ways to achieve new functionalities but with a different material: she’s leading a thrust that deals with the physical modeling of antiferromagnets, specifically chromium oxide.

“Antiferromagnets are not like your typical fridge magnet,” she says.

She explains that in fact, they’re very challenging to understand because their magnetization can’t readily be observed from the outside; they have “opposite-oriented” spins that, in effect, cancel each other out. However, they’re an exciting research area, because if you can find a way to probe them and then succeed in making devices out of them—a possibility that has been experimentally validated—those devices will work very fast. In addition, these materials’ inscrutable character and robustness to stray fields (demagnetization caused by a magnet’s own magnetic field) also offer the possibility of building secure hardware. Rakheja is modeling how chromium oxide responds to different stimuli in order to understand how it might be used.

In her new NSF project, she’s looking at a different aspect of using magnets: she aims to determine how magnetic materials and magnetic memory can support more efficient processing of big data, by putting memory close to computing elements to reduce time spent fetching data in order to compute on the data. She will also build on her earlier discovery that when she changed the inputs to the magnetic devices she’s studying, the devices acquired different functionalities—raising the exciting possibility of fabricating generic, uniform devices before their desired functionality has been selected, and then adding the functionality later. That “polymorphism”—a device’s ability to take on different roles—can offer multiple major benefits in everything from security to area efficiency.

“I am super-passionate about every single material that I’ve worked on,” says Rakheja. “I always say I’m not married to any technology or material, because I feel that every single material has such beautiful properties.”