Vortex phase transformations probed by the local ac response of Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} single crystals with various doping

TL;DR

This study investigates vortex phase transitions in Bi-2212 single crystals across different doping levels by measuring local ac responses, revealing a sharp transition at the FOT and signs of short-range order at higher fields.

Contribution

It introduces a local ac response measurement technique to probe vortex phase transitions and demonstrates doping-dependent changes in the FOT line in Bi-2212 crystals.

Findings

Step-like change in ac response at FOT temperature

Steeper FOT line with increased doping

Presence of short-range order at high fields

Abstract

The linear ac response of the vortex system is measured locally in Bi-2212 single crystals at various doping, using a miniature two-coil mutual-inductance technique. It was found that a step-like change in the local ac response takes place exactly at the first-order transition (FOT) temperature T_{FOT}(H) determined by a global dc magnetization measurement. The T_{FOT}(H) line in the H-T phase diagram becomes steeper with increasing doping. In the higher-field region where the FOT is not observed, the local ac response still shows a broadened but distinct feature, which can be interpreted to mark the growth of a short-range order in the vortex system.