Evidence of quantum vortex fluid in the mixed state of a very weakly pinned a-MoGe thin film

TL;DR

This study provides experimental evidence that vortices in a weakly pinned a-MoGe thin film can form a quantum vortex fluid, transitioning from solid to fluid states at very low temperatures, with implications for quantum fluid research.

Contribution

It demonstrates the existence of a quantum vortex fluid in a-MoGe thin films through combined magnetotransport and spectroscopy measurements, revealing new vortex state transitions at near-zero temperatures.

Findings

Vortices form a quantum fluid state at very low temperatures.

Transition from vortex solid to hexatic vortex fluid and then to isotropic vortex liquid.

Electrical resistance saturates at low temperatures indicating fluid states.

Abstract

Quantum fluids refer to a class of systems that remain in fluid state down to absolute zero temperature. In this letter, using a combination of magnetotransport and scanning tunneling spectroscopy down to 300 mK, we show that vortices in a very weakly pinned a-MoGe thin film can form a quantum vortex fluid. Under the application of a magnetic field perpendicular to the plane of the film, the vortex state transforms from a vortex solid to a hexatic vortex fluid and eventually to an isotropic vortex liquid. The fact that the two latter states remain fluid down to absolute zero temperature is evidenced from the electrical resistance which saturates to a finite value at low temperatures. Furthermore, scanning tunneling spectroscopy measurements reveal a soft gap at the center of each vortex, which arises from large zero point fluctuation of vortices.