Peak effect in single crystal MgB$_2$ superconductor for ${\bf H}\parallel c$-axis

TL;DR

This study reveals the first observation of the peak effect in the screening current of MgB$_2$ single crystals with magnetic field aligned along the c-axis, providing insights into vortex matter behavior under weak disorder.

Contribution

It reports the first detection of the peak effect in MgB$_2$ single crystals for ${\bf H}\parallel c$-axis, expanding understanding of vortex phase diagrams in type II superconductors.

Findings

Peak effect observed in MgB$_2$ for $10<H<13.5$ kOe.

Diamagnetic step transforms into a peak at higher fields.

Transition from step to gradual change below 10 kOe.

Abstract

We have studied the phase diagram of MgB$_2$ superconductor using a single crystal for ${\bf H}\parallel c$-axis. For the first time we report the existence of peak effect in the screening current in MgB$_{2}$ single crystal for ${\bf H}\parallel c$-axis. In the magnetic field regime $10<H<13.5$ kOe the local fundamental diamagnetic moment displays a very narrow diamagnetic step, with a temperature width of the same size as the zero dc-magnetic field transition. For higher field this step is transformed to a peak which is related with the peak effect in the screening current. Finally, for $H<10$ kOe the diamagnetic step is transformed to a gradual transition. Our findings for the vortex matter phase diagram for the MgB$_2$ are closely related with theoretical predictions concerning the vortex matter phase diagram of a type II superconductor in the presence of weak point disorder.