First-order vortex phase transition in Bi-2212 with low doses of correlated disorder revisited

G. RUMI; L. ALBORNOZ; P. PEDRAZZINI; H. PASTORIZA; M. KONCZYKOWSKI; C. J. VAN DER BEEK; Y. FASANO

Natal

Workshop; Poster invitado en el 16th International Workshop on Vortex Matter in Superconductors; 2017

International Institute of Physics, Natal

The impact of moderate disorder generated by a low density of columnar defects in the first-order phase transition of layered vortex matter has been the subject of various studies. The interest in this problem comes from the possibility of tuning the nature of the transition (first or second order) with controlled amount of disorder and therefore using layered vortex matter as a playground to test basic thermodynamic and structural phases in soft condensed matter. Differential magneto-optical measurements in Bi$_2$Sr$_2$CaCu$_2$O$_{8-\delta}$ suggested that for matching fields smaller than 50\,G a critical point between a first-order (low fields) and a second-order (high fields) melting transition occurs. \cite{Banerjee2003} However, direct imaging with individual vortex resolution revealed no significant changes in the in-plane structural properties of the solid vortex phase for fields larger or smaller than the critical point \cite{Menghini2003} . These latter results cast doubt on the proposal of the change of the nature of the transition being a resolution-limit or disorder-tuning driven statement. We therefore revisited this problem by applying DC and AC Hall probe local magnetization techniques in a different batch of Bi$_2$Sr$_2$CaCu$_2$O$_{8-\delta}$ samples irradiated with low doses (up to 60\,G matching fields) of columnar defects introduced by irradiation with Xe heavy ions. We find that the high-temperature paramagnetic peak in ac-transmittivity persists even for a sample with a dose of columnar defects corresponding to a 60\,G matching field. We also present preliminary results of magnetic decoration experiments in the same samples.\bibitem{Banerjee2003} S. S. Banerjee et al., Phys. Rev. Lett. 90, 87004 (2003).\bibitem{Menghini2003} M. Menghini et al., Phys. Rev. Lett. 990, 147001 (2003).