General Physics Colloquium, Professor Brad Ramshaw, Cornell University

Title:  The Sounds of Science:  Using Ultrasound to Discover Hidden Quantum Order

Host:  Dan Ralph

Abstract:  A sound wave traveling through a crystal lattice is akin to a gravity wave traveling through space: both locally distort the geometry through which particles move. Unlike space, however, crystals are densely populated with electrons whose collective behaviour responds sensitively to these distortions. As a result, ultrasound can provide deep insights into emergent quantum phenomena.

Over the past decade, my group has developed and revitalized ultrasonic techniques to study quantum materials, uncovering new insights into superconductivity, magnetism, and topological states of matter. Using this approach, we have probed the symmetry of the superconducting order parameter in UTe2, a leading candidate topological superconductor, revealing both unexpected simplicity and, under pressure, the emergence of remarkably unconventional superconducting phases. We have also developed a new ultrasound-based experiment that reveals chiral phonon dynamics and establishes connections between phonon Berry curvature and quantum magnetism.

I will conclude by discussing the directions my group is currently pursuing, the broader role of quantum materials in modern condensed matter physics, and how we can balance the complementary goals of fundamental understanding and technological impact.