# Planckian dissipation

In classical physics, there is no concept of restriction of a time interval. In principle, it can be as short as you like. An open, and absolutely fundamental, issue from many-body quantum physics is whether the same is true. The simplest ‘unit of time’ that one can construct for a quantum system in equilibrium at temperature *T *is h/(2π*k*_{B}*T)*. The key question is whether this has physical significance or not. Forefront theoretical work suggests that it does, for example in the form of a minimum ‘scrambling time’ in quantum chaos [1] and the proposed existence of a minimum possible viscosity of a strongly interacting fluid [2]. Viscosity is a measurable quantity, and experiments covering 18 orders of magnitude of temperature have given intriguing indications for a minimum scattering time, or equivalently a maximum attainable scattering rate, in systems as diverse as laser-cooled atoms at 10^{-6} K and the quark-gluon plasma at 10^{12} K. The term ‘Planckian dissipation’ has been coined to describe the concept of this maximal scattering rate.

Sitting near the middle of this range, strongly interacting electrons in solids can also be used to examine the concept of Planckian dissipation, and measurements of electrical transport across a wide range of materials again give tantalising evidence for its existence [3,4]. This is exciting because there remains much to understand, and a far more in-depth investigation is possible in solids than in the above-mentioned systems. In principle we can cover 3-4 orders of magnitude of temperature studying the same material, and test the interplay between scattering mechanisms of different microscopic origins. That is the goal of this project. By studying electrical resistivity, thermal conductivity, heat capacity and thermal diffusivity in carefully selected materials with controlled levels of crystalline disorder, it should be possible to obtain fundamental insights into this key quantum many-body concept.

## References

**8**, 106 (2016)

**94**, 111601 (2005)

**339**, 804 (2013)

**15**, 142 (2019)