The Origin of Planckian Scattering in Strange Metals

Non-technical abstract

“Limits” play an important role in physics, just like speed limits play an important role on our roads. For example, nothing can move faster than the speed of light. This limit was the basis of Einstein’s theory of relatively, and it governs everything from how we do astronomy to how we build nuclear reactors.

Recently, a new type of limit has emerged called the “Planckian limit”. This proposed limit states that electrons can “run into” each other in a metal no faster than an amount set by the temperature of the metal and fundamental constants of nature – Planck and Boltzmann’s constants. This limit, if it holds true, has implications for physics problems as broad as finding room-temperature superconductors to how quickly quantum information can be transported.

This project uses the world’s strongest magnetic fields and ultrasound to test whether the Planckian limit really is a limit and, if so, what underlying physical laws give rise to such a limit. This research will train the next generation of physicists in high-frequency electronics and quantum materials and will develop outreach activities for high school-student workshops held at Cornell.

Technical abstract

Strange metals have electrical resistivity that is linear in temperature (T-linear) all the way down to zero temperature. This distinctive behavior often appears in conjunction with unconventional superconductivity: high-temperature superconducting cuprates, iron pnictides, organics, heavy fermions, and magic angle twisted bilayer graphene all have T-linear resistivity in their phase diagrams near where the transition temperature is maximized.

One captivating idea is that of a “Planckian bound” – a universal upper limit on electron scattering in metals. Such a bound, if it exists, could explain why such disparate systems all show universal T-linear resistivity. This proposal combines high magnetic field electrical transport experiments with state-of-the-art, high-frequency ultrasound to uncover what causes T-linear resistivity, why it appears to follow a fundamental “Planckian bound”, and how strange metals evolve into conventional metals as their carrier density is tuned.

These experiments will broaden our understanding of how strange metals arise and whether they obey a new fundamental bound.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.