Physics' Xuemei Cheng: From Semiconductors to Spintronics and Quantum Computing

Xuemei May Cheng  is the Dean of Graduate Studies, Professor of Physics, and the Rachel C. Hale Professor in the Sciences and Mathematics. She will be giving an endowed lecture titled "Twisters: Explore Nanomaterials for Data Storage and Quantum Computing" on Monday, March 3.

Growing up in Huaiyin, China, Bryn Mawr College Professor of Physics Xuemei May Cheng had an early interest in figuring out how things work. Cheng spent her childhood evenings watching her father meticulously tinker with tiny semiconductor components, carefully assembling them into a working TV. From this, her passion grew to understand the mechanics of everything, from electronics to the universe itself.

"Materials science has fascinated me since I was a little kid," says Cheng. "At just three or four years old, I would watch my dad assemble TVs and radios using semiconductor devices, and that was always amazing to me."

If Cheng could get her hands on something, she would dive right in. One day, she was dismantling semiconductors; the next, she was experimenting with ingredients in the kitchen to create meals. By the age of five, she had even knitted her own pair of gloves.

As a teen, Cheng challenged longstanding stereotypes regarding women in STEM. She credits her confidence in pursuing science to her family.

“Unfortunately, many people think or used to think that STEM fields are for men and boys,” says Cheng. “I was fortunate growing up that my family has a tradition of producing engineers—my brother, my cousin, my parents. They are all engineers. I already had a familiarity with science and math because of this.”

But it wasn’t until college that physics became Cheng’s front-running science.

“I honestly did not see myself as a physicist for a long time. I thought I might be a biologist or maybe even work in medicine," she recalls. "My mom had been sick for a while, and during that time the medical field really resonated with me.”

Cheng’s freshman year at Nanjing University, however, turned the tide. Enrolled in the highly selective Department for Intensive Instruction, now the Kuang Yaming Honors School, a program designed to nurture future STEM faculty, she was guided by her introductory physics professor and department chair, Professor Dexin Lu. He encouraged students to approach each homework problem as a research topic, stressing the importance of not just solving calculations but reflecting on their implications. This mindset transformed physics from a set of equations into a profound way of thinking.

“Professor Lu sat down with me for half a day to convince me to be a physics major. I felt honored that he felt so confident in me and my abilities, and I wanted to meet his expectations, so I declared physics as my major in my junior year," she says.

Like her father, Cheng’s interest in physics focused on semiconductors. She first worked on semiconductor materials with tunable energy band gaps for infrared detectors, which resulted in her first published research in Applied Physics Letters.

“My first publication was when I was a master’s student at Nanjing University. I was following a Ph.D. student to grow epitaxial SiGeC alloy films on silicon substrates,” she says.

To identify a unique angle for her master’s project, she spent many days in the library, searching for research literature. She designed to anneal and oxidize the SiGeC films in an oven and study the photoluminescence (PL) of these materials. She independently conducted the experiment, PL spectra measurements, and data analysis. She credits this experience for shaping her entire career.

After earning her master’s in microelectronics and solid-state electronics from Nanjing University, Cheng moved across the world to pursue her Ph.D. degree at Johns Hopkins University.

At Johns Hopkins, Cheng’s field of study shifted to nanomagnetism. With the goal of developing the next generation of spintronic devices, she researched the magnetic properties of nanomaterials.

"Semiconductor-based electronics rely on the charge of electrons," she explains, "while spintronics harnesses their intrinsic spin, offering higher speeds and lower energy consumption for magnetic data storage."

Combining her experience in semiconductor materials and curiosity for magnetic nanomaterials, she proposed to her Ph.D. advisor, Prof. Chia-Ling Chien, to explore diluted magnetic semiconductor thin films. She started from scratch, sputtering Mn-doped ZnO thin films and investigating their magnetic properties. Her hard work paid off.

“Finally, I made my first professional presentation at the 2002 Conference on Magnetism and Magnetic Materials, and it was very well received. Afterward, Dr. Jagadeesh Moodera from MIT approached me and asked me if I was interested in joining his group as a postdoctoral researcher. As I was only a second-year graduate student then, my advisor joked with Dr. Moodera that he had to be patient to wait for five years,” says Cheng.

Cheng continued her experimental exploration of magnetic nanomaterials and completed her Ph.D. dissertation on the magnetization reversal and magnetotransport properties of Co/Pt multilayers with perpendicular magnetic anisotropy. Afterward, she expanded her expertise in synchrotron X-ray techniques during her postdoctoral research at Argonne National Laboratory.

Cheng joined the faculty of Bryn Mawr College in 2009. Her research career has culminated in a $5 million National Science Foundation Grant for establishing a Research and Education Center for Quantum Materials and Sensing at Bryn Mawr. In addition to continuing her research in nanomaterials, her professorship at Bryn Mawr has provided her with great opportunities to educate the next generation of women interested in the sciences. Over the past 15 years, she has mentored nearly 50 undergraduate students in research, most of whom have gone on to Ph.D. programs in engineering and physics at institutions such as Princeton, Harvard, MIT, Columbia, UPenn, UCLA, and Rice.

“My research students all have bright futures; some have become tenure-track professors, while others have moved into industry, working with companies like Apple. Whenever I hear about their achievements, I feel so proud of them," she says.