Phase Diagram of Heavy-Ion Irradiated Bi_2Sr_2CaCu_2O_8

TL;DR

This study maps the phase diagram of Bi_2Sr_2CaCu_2O_8 single crystals with heavy-ion induced defects, revealing how vortex pinning and entropy contributions vary with defect density and magnetic field.

Contribution

It provides new insights into vortex behavior and phase transitions in irradiated high-temperature superconductors through combined magnetization measurements.

Findings

Entropy contribution is minor in the London regime for both unirradiated and irradiated crystals.

High defect density and low magnetic fields increase entropy effects.

Irreversibility line H_irr sharply increases at the interaction field H_int.

Abstract

Using dynamic and thermodynamic magnetization measurements, we analyze the phase diagram of Bi_2Sr_2CaCu_2O_8delta single crystals containing amorphous columnar defects created by heavy-ion irradiation. Reversible magnetization experiments yield the respective magnitudes of the pinning energy and entropy contributions to the free energy of the vortex lattice. It appears that the entropy contribution in the London regime is relatively minor in both unirradiated and irradiated crystals, except in the case of high density of columns and inductions B that are smaller than the interaction field H_int ~ B_phi / 6. The dependence of the entropy contribution on vortex- and defect density correlates well with measurements of the irreversibility line H_irr, which shows a sharp increase at H_int.