Alumnus Arjun Raghavan wins Nottingham Prize

Illinois Physics alumnus Arjun Raghavan (Ph.D. 2025) won the prestigious Nottingham Prize at the 85th Annual Physical Electronics Conference, held August 18–21 at the University of California, San Diego. 

Named in honor of Massachusetts Institute of Technology Professor Wayne B. Nottingham 1899–1964), the prize recognizes the best scientific paper based on current or recent doctoral thesis research presented at the conference. The prize comprises a certificate and $1,500. Past winners have gone on to become leaders in the field of surface science.

Raghavan received the award for his presentation of the as-yet unpublished research article, “Dynamic competition between phason and amplitudon observed by ultrafast multimodal scanning tunneling microscopy,” based on research conducted in the group of Illinois Physics Professor Vidya Madhavan. Raghavan is currently a Texas Quantum Institute postdoctoral fellow at the University of Texas at Austin, working in the group of Physics Professor Edoardo Baldini.

The winning research introduces a multimodal scanning tunneling microscopy (STM) pump-probe technique that combines three measurement methods in one instrument: ultrafast tunneling microscopy, ultrafast point-contact spectroscopy, and optical pump-probe reflectance. The researchers used the technique to study collective excitations in the unconventional charge-density-wave insulator (TaSe₄)₂I.

The non-invasive technique developed by the team represents a major step forward, providing real-time images of excited electrons.

The instrument was constructed by postdoctoral researcher Seokjin Bae and Raghavan between 2020 and 2024. Earlier ultrafast STM studies were primarily limited to semiconductors and molecules adsorbed on surfaces. Raghavan and colleagues further developed the instrument to enable the study of electrons interacting in quantum materials. The Illinois instrument incorporates sequences of ultrafast light pulses and lenses close to the sample inside the ultrahigh vacuum chamber, allowing the researchers to focus a laser beam tightly on the sample to excite electrons, without heating extended regions of the sample.

“The instrument can capture the ultrafast and ultrasmall simultaneously,” Raghavan said. “We can capture information about electrons moving on timescales of less than a trillionth of one second with a spatial resolution of less than a billionth of one foot.”

The research team explored various materials, before finally collecting the data reported in the study in 2024 and 2025. Bae and Raghavan are co-first authors of the preprint.

The scientists observed charge oscillations at a frequency of 0.22 terahertz, consistent with the theoretically predicted low-temperature behavior of a massive phason that has acquired an energy gap through the Anderson-Higgs mechanism. A phason is a collective excitation that behaves like a particle (called a quasiparticle) associated with the phase (lateral sliding motion) of a charge-density wave. They also directly imaged a second mode at 0.11 terahertz, a “daughter mode” arising from the splitting of the 0.22-terahertz massive phason into two massless phasons through parametric amplification.

The researchers further found that the daughter mode phason competes with and suppresses an amplitudon at a nearby frequency. An amplitudon is a quasiparticle associated with oscillations in the amplitude of a charge-density wave.

Raghavan notes, although this work is fundamental in nature, it could potentially have implications for the miniaturization of devices, where electron interactions at the nanoscale can affect optimal performance.

“We visualized how electrons start to slide in a coherent oscillatory motion at low temperatures and how different oscillatory modes can compete with each other for energy provided by laser excitation,” he said.

The research was a significant part of Raghavan’s doctoral thesis, which he defended in August 2025. In addition to Raghavan and Bae, the paper's authors include Illinois Physics Professors Barry Bradlyn, Fahad Mahmood, and Madhavan, former Illinois Physics postdoctoral researcher Soyeun Kim and former Illinois Physics graduate student Kejian Qu; Illinois Materials Science and Engineering Professor Daniel Shoemaker and Illinois MatSE graduate student Chengxi Zhao; and Boston College Physics Professor Ziqiang Wang.

This research was funded by the Gordon and Betty Moore Foundation’s EPiQS initiative, the Department of Energy (DOE) Office of Science, and by the National Science Foundation, Any opinions, findings, and conclusions or recommendations expressed are those of the author and do not necessarily reflect the views of the funding agencies.