Transport in clean quantum critical superfluids

Specialist level
Eric Mefford
École Polytechnique Paris



 The hydrodynamic regime of superfluids in systems like 4He has been well understood since the seminal work of Landau and Tisza. A fundamental assumption in much subsequent work is the low-temperature dominance of the superfluid phonon which leads to universal behavior in transport that is characterized by the phonon sound speed. I will discuss investigations of the two-fluid model of superfluids near an underlying quantum critical phase and establish criteria for the breakdown of this assumption which leads to novel transport behavior. A surprising result is the non-vanishing of the charge density of the fluid’s normal component at zero temperature. I will illustrate these results with some holographic models.