# Field-induced gapless electron pocket in the superconducting vortex phase of YNi2B2C as probed by magnetoacoustic quantum oscillations

## TL;DR

This study uses magneto-acoustic quantum oscillations to investigate the superconducting vortex phase of YNi2B2C, revealing a field-induced gapless electron pocket in one of its bands, contrasting previous torque magnetometry results.

## Contribution

It provides direct evidence of a nearly gapless band in YNi2B2C's mixed state using ultrasound, highlighting differences with torque magnetometry findings.

## Key findings

- Weak damping of oscillations indicates a small or vanishing gap in the alpha band.
- Magneto-acoustic data suggest a stable electron pocket in the vortex phase.
- Contrasts with torque magnetometry results due to flux-line lattice distortions.

## Abstract

By use of ultrasound studies we resolved magneto-acoustic quantum oscillation deep into the mixed state of the multiband nonmagnetic superconductor YNi2B2C. Below the upper critical field, only a very weak additional damping appears that can be well explained by the field inhomogeneity caused by the flux-line lattice in the mixed state. This is clear evidence for no or a vanishingly small gap for one of the bands, namely, the spheroidal alpha band. This contrasts de Haas--van Alphen data obtained by use of torque magnetometry for the same sample, with a rapidly vanishing oscillation signal in the mixed state. This points to a strongly distorted flux-line lattice in the latter case that, in general, can hamper a reliable extraction of gap parameters by use of such techniques.