Transverse Quantum Superfluids

TL;DR

This paper introduces the concept of transverse quantum fluids (TQF), a new class of superfluid states characterized by infinite compressibility and unusual properties, observed in systems like dislocation cores in solid helium-4.

Contribution

It defines the TQF state, explores its unique properties, and challenges traditional superfluidity paradigms, broadening understanding of quantum fluid behavior in condensed matter.

Findings

TQF exhibits infinite compressibility and quadratic or absent normal modes.

Normal superfluid criteria like Landau's are irrelevant for TQF.

TQF demonstrates off-diagonal long-range order at zero temperature.

Abstract

Even when ideal solids are insulating, their states with crystallographic defects may have superfluid properties. It became clear recently that edge dislocations in $^4$He featuring a combination of microscopic quantum roughness and superfluidity of their cores may represent a new paradigmatic class of quasi-one-dimensional superfluids. The new state of matter, termed transverse quantum fluid (TQF), is found in a variety of physical setups. The key ingredient defining the class of TQF systems is infinite compressibility, which is responsible for all other unusual properties such as the quadratic spectrum (or even the absence) of normal modes, irrelevance of the Landau criterion, off-diagonal long-range order at $T = 0$, and the exponential dependence of the phase slip probability on the inverse flow velocity. From a conceptual point of view, the TQF state is a striking demonstration of the conditional character of many dogmas associated with superfluidity, including the necessity of elementary excitations, in general, and the ones obeying Landau criterion in particular.