Transverse Quantum Fluid

The concept of Transverse Quantum Fluid (TQF) [1] is a generic description of superfluidity along a boundary of insulator in the situation when this boundary can move freely in its transverse direction due to the exchanging matter with the insulator. We have called such a relation between the superflow along the boundary and its transverse motion as superclimb [2]. The TQF spectrum of excitations along the boundary is parabolic rather than linear. The first example of such a 1D liquid embedded into 3D crystal came from the description of the superclimbing edge dislocation in solid ⁴He [2]. This system is characterized by the gigantic compressibility – the response on chemical potential [1,2], the ODLRO at zero temperature and the robustness of the superflow with respect to the phase slips in spite of the parabolic dispersion [1]. As it turns out, many other systems exhibit similar properties---boundaries in phase separated lattice states, magnetic domain walls (see Fig.1A), and ensembles of Luttinger Liquids (LL) [3] (see Fig.1B). The latter example, while carrying close similarities with the properties of the superclimbing domain walls (or the dislocations), is characterized by the lack of well-defined excitations at low energies---its spectrum is diffusive. An incoherent TQF is a striking example of the irrelevance of the Landau quasiparticle criterion for superfluidity in systems that lack Galilean invariance. I will detail the phenomenology of 1D TQF (see in [3,4]), to motivate a number of experimental studies in condensed matter and cold atomic systems.