Finding the elusive sliding phase in superfluid-normal phase transition smeared by c-axis disorder

TL;DR

This paper investigates how c-axis disorder in layered superfluids causes the superfluid-normal phase transition to smear into a Griffiths phase, leading to a novel sliding superfluid with anisotropic properties.

Contribution

The study develops a functional renormalization group approach to analyze disorder effects, revealing the emergence of a sliding Griffiths superfluid phase with unique anisotropic characteristics.

Findings

Disorder smears the phase transition into a Griffiths phase.

Emergence of a sliding superfluid with anisotropic critical current.

Finite in-plane stiffness and vanishing perpendicular stiffness in the Griffiths phase.

Abstract

We consider a system composed of a stack of weakly Josephson coupled superfluid layers with c-axis disorder in the form of random superfluid stiffnesses and vortex fugacities in each layer as well as random inter-layer coupling strengths. In the absence of disorder this system has a 3D XY type superfluid-normal phase transition as a function of temperature. We develop a functional renormalization group to treat the effects of disorder, and demonstrate that the disorder results in the smearing of the superfluid normal phase transition via the formation of a Griffiths phase. Remarkably, in the Griffiths phase, the emergent power-law distribution of the inter-layer couplings gives rise to sliding Griffiths superfluid, with an anisotropic critical current, and with a finite stiffness in a-b direction along the layers, and a vanishing stiffness perpendicular to it.