Physics Colloquium with Vidya Madhavan

What connects the redshift of distant galaxies, the rising and falling pitch of a passing train, and the effects of Cooper pairs moving inside a superconductor? A single unifying idea: the Doppler effect. First identified in the 19th century, the Doppler shift has become a powerful tool for probing motion, from measuring the velocities of receding stars to tracking waves in everyday life, as with the dreaded police radar. At its core, the Doppler effect predicts that when a source of a wave (whether sound, light, or a quasiparticle excitation) is in motion relative to an observer, the observer measures a shift in the wave's frequency. In this talk, I’ll show how this familiar principle can become a precision probe in an unexpected setting: triplet superconductors.

Spin-triplet superconductivity is a condensate of electron pairs with spin 1 and an odd-parity wavefunction. A particularly interesting manifestation of triplet pairing is a topologically nontrivial superconductor, which provides a natural platform for realizing Majorana fermions. Spin-triplet superconductors are rare, but uranium ditelluride (UTe₂) shows signs of potentially being one.

I will describe our recent scanning tunneling microscopy studies of UTe₂. I will show how we can use the Doppler shift to measure the orbital character of the Cooper pairs and demonstrate that our findings are consistent with triplet pairing. I will then address the question of the topological properties of this superconductor and present direct evidence for the presence of states inside the superconducting gap that are likely composed of Majorana fermions.

About the speaker:

Professor Madhavan is an experimental condensed matter physicist who uses scanning tunneling microscopy and spectroscopy to study the electronic properties of quantum materials at the atomic scale. She earned her PhD from Boston University in 2000 and held a postdoctoral appointment at UC Berkeley. She joined the physics faculty at Boston College in 2002 and moved to Illinois as a full professor in 2014.

Her honors include an NSF CAREER Award and selection as an Experimental Investigator by the Gordon and Betty Moore Foundation. She was named a Fellow of the American Physical Society in 2015 and was elected to the U.S. National Academy of Sciences in 2026.