Doping dependence of the vortex glass and sublimation transitions in the high-$T_{c}$ superconductor La$_{2-x}$Sr$_{x}$CuO$_{4}$ as determined from macroscopic measurements

TL;DR

This study investigates how doping levels affect the vortex phase transitions in La$_{2-x}$Sr$_{x}$CuO$_{4}$ superconductor, revealing a doping-dependent phase diagram and identifying sublimation and vortex glass transitions through macroscopic measurements.

Contribution

It provides the first detailed doping-dependent phase diagram of vortex transitions in La$_{2-x}$Sr$_{x}$CuO$_{4}$ using magnetization and ac-susceptibility data, highlighting sublimation and vortex glass phenomena.

Findings

Doping influences the vortex phase diagram significantly.

Vortex lattice sublimation occurs instead of melting in this material.

The second peak correlates with a transition to a vortex glass state.

Abstract

Magnetization and ac-susceptibility measurements are used to characterize the mixed phase of the high-temperature cuprate superconductor La$_{2-x}$Sr$_{x}$CuO$_{4}$ over a large range of doping (0.075 $\leq x\leq$ 0.20). The first order vortex lattice phase transition line $H_{FOT}(T)$, the upper critical field $H_{c2}(T)$ and the second peak $H_{sp}(T)$ have been investigated up to high magnetic fields (8 Tesla applied perpendicular to the $CuO_2$ planes). Our results reveal a strong doping dependence of the magnetic phase diagram, which can mainly be explained by the increasing anisotropy with underdoping. Within our interpretation, the first order vortex lattice phase transition is due to the sublimation (rather than melting) of the vortex lattice into a gas of pancake vortices, whereas the second peak is related to the transition to a more disordered vortex glass state.