SFB Extra Seminar

Despite the chaotic nature of the microscopic dynamics, it is well known that large numbers of interacting classical "molecules" form fluids and exhibit collective behavior on long length scales.  Why can't we apply a similar collective description to the quantum fluid of electrons in a solid state system?  Such a collective understanding of electron flow would solve questions about electrical and thermal transport which are notoriously hard to address in our conventional formalism.  As I will review, electrons do appear to flow like fluids in a number of experimental systems, as explored in a burst of experimental activity in the past few years.

How are we to tell that electrons behave like a classical fluid?  What fluid equations of motion do they obey?  I will show that the answers to these questions can be "exotic" and new kinds of hydrodynamics beyond the ordinary Navier-Stokes equations may be accessible in electronic systems.  I will discuss the emergence of relativistic hydrodynamics for nearly charge neutral plasmas in graphene:  the so-called "Dirac fluid".   I will describe a cartoon of the onset of hydrodynamic flow of electrons in a metal with a polygon Fermi surface, and explain the emergence of additional dissipative components of viscosity which are strictly forbidden in classical fluids, along with exotic long-lived "quasihydrodynamic" modes.  This cartoon is relevant for materials such as PdCoO2; as such, I will revisit the evidence for hydrodynamic flow in this material.